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"Previous Section"_Install.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc - "Next Section"_Run_head.html :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Build LAMMPS :h2
LAMMPS can be built as an executable or library from source code via
either traditional makefiles (which may require manual editing)
for use with GNU make or gmake, or a build environment generated by CMake
(Unix Makefiles, Xcode, Visual Studio, KDevelop or more). As an
alternative you can download a package with pre-built executables
as described on the "Install"_Install.html doc page.
<!-- RST
.. toctree::
:maxdepth: 1
Build_cmake
Build_make
Build_link
Build_basics
Build_settings
Build_package
Build_extras
Build_windows
Build_development
END_RST -->
<!-- HTML_ONLY -->
"Build LAMMPS with CMake"_Build_cmake.html
"Build LAMMPS with make"_Build_make.html
"Link LAMMPS as a library to another code"_Build_link.html
"Basic build options"_Build_basics.html
"Optional build settings"_Build_settings.html
"Include packages in build"_Build_package.html
"Packages with extra build options"_Build_extras.html
"Notes for building LAMMPS on Windows"_Build_windows.html
"Development build options (CMake only)"_Build_development.html :all(b)
If you have problems building LAMMPS, it is often due to software
issues on your local machine. If you can, find a local expert to
help. If you're still stuck, send an email to the "LAMMPS mail
list"_http://lammps.sandia.gov/mail.html.

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"Higher level section"_Build.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Basic build options :h3
The following topics are covered on this page, for building both with
CMake and make:
"Serial vs parallel build"_#serial
"Choice of compiler and compile/link options"_#compile
"Build LAMMPS as an executable or a library"_#exe
"Build the LAMMPS documentation"_#doc
"Install LAMMPS after a build"_#install :ul
:line
Serial vs parallel build :h4,link(serial)
LAMMPS can be built to run in parallel using the ubiquitous "MPI
(message-passing
interface)"_https://en.wikipedia.org/wiki/Message_Passing_Interface
library. Or it can built to run on a single processor (serial)
without MPI. It can also be built with support for OpenMP threading
(see more discussion below).
[CMake variables]:
-D BUILD_MPI=value # yes or no, default is yes if CMake finds MPI, else no
-D BUILD_OMP=value # yes or no (default)
-D LAMMPS_MACHINE=name # name = mpi, serial, mybox, titan, laptop, etc
# no default value :pre
The executable created by CMake (after running make) is lmp_name. If
the LAMMPS_MACHINE variable is not specified, the executable is just
lmp. Using BUILD_MPI=no will produce a serial executable.
[Traditional make]:
cd lammps/src
make mpi # parallel build, produces lmp_mpi using Makefile.mpi
make serial # serial build, produces lmp_serial using Makefile/serial
make mybox :pre # uses Makefile.mybox to produce lmp_mybox :pre
Serial build (see src/MAKE/Makefile.serial):
MPI_INC = -I../STUBS
MPI_PATH = -L../STUBS
MPI_LIB = -lmpi_stubs :pre
For a parallel build, if MPI is installed on your system in the usual
place (e.g. under /usr/local), you do not need to specify the 3
variables MPI_INC, MPI_PATH, MPI_LIB. The MPI wrapper on the compiler
(e.g. mpicxx, mpiCC) knows where to find the needed include and
library files. Failing this, these 3 variables can be used to specify
where the mpi.h file (MPI_INC), and the MPI library files (MPI_PATH)
are found, and the name of the library files (MPI_LIB).
For a serial build, you need to specify the 3 variables, as shown
above.
For a serial LAMMPS build, use the dummy MPI library provided in
src/STUBS. You also need to build the STUBS library for your platform
before making LAMMPS itself. A "make serial" build does this for.
Otherwise, type "make mpi-stubs" from the src directory, or "make"
from the src/STUBS dir. If the build fails, you will need to edit the
STUBS/Makefile for your platform.
The file STUBS/mpi.c provides a CPU timer function called MPI_Wtime()
that calls gettimeofday() . If your system doesn't support
gettimeofday() , you'll need to insert code to call another timer.
Note that the ANSI-standard function clock() rolls over after an hour
or so, and is therefore insufficient for timing long LAMMPS
simulations.
[CMake and make info]:
If you are installing MPI yourself, we recommend MPICH2 from Argonne
National Laboratory or OpenMPI. MPICH can be downloaded from the
"Argonne MPI site"_http://www.mcs.anl.gov/research/projects/mpich2/.
OpenMPI can be downloaded from the "OpenMPI
site"_http://www.open-mpi.org. Other MPI packages should also work.
If you are running on a large parallel machine, your system admins or
the vendor should have already installed a version of MPI, which is
likely to be faster than a self-installed MPICH or OpenMPI, so find
out how to build and link with it.
The majority of OpenMP (threading) support in LAMMPS is provided by
the USER-OMP package; see the "Speed omp"_Speed_omp.html doc page for
details. The USER-INTEL package also provides OpenMP support (it is
compatible with USER-OMP) and adds vectorization support when compiled
with the Intel compilers on top of that. Also, the KOKKOS package can
be compiled for using OpenMP threading.
However, there are a few commands in LAMMPS that have native OpenMP
support. These are commands in the MPIIO, SNAP, USER-DIFFRACTION, and
USER-DPD packages. In addition some packages support OpenMP threading
indirectly through the libraries they interface to: e.g. LATTE and
USER-COLVARS. See the "Packages details"_Packages_details.html doc
page for more info on these packages and the doc pages for their
respective commands for OpenMP threading info.
For CMake, if you use BUILD_OMP=yes, you can use these packages and
turn on their native OpenMP support and turn on their native OpenMP
support at run time, by setting the OMP_NUM_THREADS environment
variable before you launch LAMMPS.
For building via conventional make, the CCFLAGS and LINKFLAGS
variables in Makefile.machine need to include the compiler flag that
enables OpenMP. For GNU compilers it is -fopenmp. For (recent) Intel
compilers it is -qopenmp. If you are using a different compiler,
please refer to its documentation.
[OpenMP Compiler compatibility info]: :link(default-none-issues)
Some compilers do not fully support the 'default(none)' directive
and others (e.g. GCC version 9 and beyond) may implement OpenMP 4.0
semantics, which are incompatible with the OpenMP 3.1 directives used
in LAMMPS (for maximal compatibility with compiler versions in use).
In those case, all 'default(none)' directives (which aid in detecting
incorrect and unwanted sharing) can be replaced with 'default(shared)'
while dropping all 'shared()' directives. The script
'src/USER-OMP/hack_openmp_for_pgi_gcc9.sh' can be used to automate
this conversion.
:line
Choice of compiler and compile/link options :h4,link(compile)
The choice of compiler and compiler flags can be important for
performance. Vendor compilers can produce faster code than
open-source compilers like GNU. On boxes with Intel CPUs, we suggest
trying the "Intel C++ compiler"_intel.
:link(intel,https://software.intel.com/en-us/intel-compilers)
On parallel clusters or supercomputers which use "modules" for their
compile/link environments, you can often access different compilers by
simply loading the appropriate module before building LAMMPS.
[CMake variables]:
-D CMAKE_CXX_COMPILER=name # name of C++ compiler
-D CMAKE_C_COMPILER=name # name of C compiler
-D CMAKE_Fortran_COMPILER=name # name of Fortran compiler :pre
-D CMAKE_CXX_FLAGS=string # flags to use with C++ compiler
-D CMAKE_C_FLAGS=string # flags to use with C compiler
-D CMAKE_Fortran_FLAGS=string # flags to use with Fortran compiler :pre
By default CMake will use a compiler it finds and it will add
optimization flags appropriate to that compiler and any "accelerator
packages"_Speed_packages.html you have included in the build.
You can tell CMake to look for a specific compiler with these variable
settings. Likewise you can specify the FLAGS variables if you want to
experiment with alternate optimization flags. You should specify all
3 compilers, so that the small number of LAMMPS source files written
in C or Fortran are built with a compiler consistent with the one used
for all the C++ files:
Building with GNU Compilers:
cmake ../cmake -DCMAKE_C_COMPILER=gcc -DCMAKE_CXX_COMPILER=g++ -DCMAKE_Fortran_COMPILER=gfortran
Building with Intel Compilers:
cmake ../cmake -DCMAKE_C_COMPILER=icc -DCMAKE_CXX_COMPILER=icpc -DCMAKE_Fortran_COMPILER=ifort
Building with LLVM/Clang Compilers:
cmake ../cmake -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_Fortran_COMPILER=flang :pre
NOTE: When the cmake command completes, it prints info to the screen
as to which compilers it is using, and what flags will be used in the
compilation. Note that if the top-level compiler is mpicxx, it is
simply a wrapper on a real compiler. The underlying compiler info is
what will be listed in the CMake output. You should check to insure
you are using the compiler and optimization flags are the ones you
want.
[Makefile.machine settings]:
Parallel build (see src/MAKE/Makefile.mpi):
CC = mpicxx
CCFLAGS = -g -O3
LINK = mpicxx
LINKFLAGS = -g -O :pre
Serial build (see src/MAKE/Makefile.serial):
CC = g++
CCFLAGS = -g -O3
LINK = g++
LINKFLAGS = -g -O :pre
The "compiler/linker settings" section of a Makefile.machine lists
compiler and linker settings for your C++ compiler, including
optimization flags. You should always use mpicxx or mpiCC for
a parallel build, since these compiler wrappers will include
a variety of settings appropriate for your MPI installation.
NOTE: If you build LAMMPS with any "accelerator
packages"_Speed_packages.html included, they have specific
optimization flags that are either required or recommended for optimal
performance. You need to include these in the CCFLAGS and LINKFLAGS
settings above. For details, see the individual package doc pages
listed on the "Speed packages"_Speed_packages.html doc page. Or
examine these files in the src/MAKE/OPTIONS directory. They
correspond to each of the 5 accelerator packages and their hardware
variants:
Makefile.opt # OPT package
Makefile.omp # USER-OMP package
Makefile.intel_cpu # USER-INTEL package for CPUs
Makefile.intel_coprocessor # USER-INTEL package for KNLs
Makefile.gpu # GPU package
Makefile.kokkos_cuda_mpi # KOKKOS package for GPUs
Makefile.kokkos_omp # KOKKOS package for CPUs (OpenMP)
Makefile.kokkos_phi # KOKKOS package for KNLs (OpenMP) :pre
:line
Build LAMMPS as an executable or a library :h4,link(exe)
LAMMPS can be built as either an executable or as a static or shared
library. The LAMMPS library can be called from another application or
a scripting language. See the "Howto couple"_Howto_couple.html doc
page for more info on coupling LAMMPS to other codes. See the
"Python"_Python_head.html doc page for more info on wrapping and
running LAMMPS from Python via its library interface.
[CMake variables]:
-D BUILD_EXE=value # yes (default) or no
-D BUILD_LIB=value # yes or no (default)
-D BUILD_SHARED_LIBS=value # yes or no (default)
-D LAMMPS_LIB_SUFFIX=name # name = mpi, serial, mybox, titan, laptop, etc
# no default value :pre
Setting BUILD_EXE=no will not produce an executable. Setting
BUILD_LIB=yes will produce a static library named liblammps.a.
Setting both BUILD_LIB=yes and BUILD_SHARED_LIBS=yes will produce a
shared library named liblammps.so. If LAMMPS_LIB_SUFFIX is set the generated
libraries will be named liblammps_name.a or liblammps_name.so instead.
[Traditional make]:
cd lammps/src
make machine # build LAMMPS executable lmp_machine
make mode=lib machine # build LAMMPS static lib liblammps_machine.a
make mode=shlib machine # build LAMMPS shared lib liblammps_machine.so :pre
The two library builds also create generic soft links, named
liblammps.a and liblammps.so, which point to the liblammps_machine
files.
[CMake and make info]:
Note that for a shared library to be usable by a calling program, all
the auxiliary libraries it depends on must also exist as shared
libraries. This will be the case for libraries included with LAMMPS,
such as the dummy MPI library in src/STUBS or any package libraries in
the lib/packages directory, since they are always built as shared
libraries using the -fPIC switch. However, if a library like MPI or
FFTW does not exist as a shared library, the shared library build will
generate an error. This means you will need to install a shared
library version of the auxiliary library. The build instructions for
the library should tell you how to do this.
As an example, here is how to build and install the "MPICH
library"_mpich, a popular open-source version of MPI, distributed by
Argonne National Lab, as a shared library in the default
/usr/local/lib location:
:link(mpich,http://www-unix.mcs.anl.gov/mpi)
./configure --enable-shared
make
make install :pre
You may need to use "sudo make install" in place of the last line if
you do not have write privileges for /usr/local/lib. The end result
should be the file /usr/local/lib/libmpich.so.
:line
Build the LAMMPS documentation :h4,link(doc)
[CMake variable]:
-D BUILD_DOC=value # yes or no (default) :pre
This will create the HTML doc pages within the CMake build directory.
The reason to do this is if you want to "install" LAMMPS on a system
after the CMake build via "make install", and include the doc pages in
the install.
[Traditional make]:
cd lammps/doc
make html # html doc pages
make pdf # single Manual.pdf file :pre
This will create a lammps/doc/html dir with the HTML doc pages so that
you can browse them locally on your system. Type "make" from the
lammps/doc dir to see other options.
NOTE: You can also download a tarball of the documentation for the
current LAMMPS version (HTML and PDF files), from the website
"download page"_http://lammps.sandia.gov/download.html.
:line
Build LAMMPS tools :h4,link(tools)
Some tools described in "Auxiliary tools"_Tools.html can be built directly
using CMake or Make.
[CMake variable]:
-D BUILD_TOOLS=value # yes or no (default) :pre
The generated binaries will also become part of the LAMMPS installation (see below)
[Traditional make]:
cd lammps/tools
make all # build all binaries of tools
make binary2txt # build only binary2txt tool
make chain # build only chain tool
make micelle2d # build only micelle2d tool
make thermo_extract # build only thermo_extract tool
:pre
:line
Install LAMMPS after a build :h4,link(install)
After building LAMMPS, you may wish to copy the LAMMPS executable of
library, along with other LAMMPS files (library header, doc files) to
a globally visible place on your system, for others to access. Note
that you may need super-user privileges (e.g. sudo) if the directory
you want to copy files to is protected.
[CMake variable]:
cmake -D CMAKE_INSTALL_PREFIX=path \[options ...\] ../cmake
make # perform make after CMake command
make install # perform the installation into prefix :pre
[Traditional make]:
There is no "install" option in the src/Makefile for LAMMPS. If you
wish to do this you will need to first build LAMMPS, then manually
copy the desired LAMMPS files to the appropriate system directories.

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"Higher level section"_Build.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Build LAMMPS with CMake :h3
This page is a short summary of how to use CMake to build LAMMPS.
Details on CMake variables that enable specific LAMMPS build options
are given on the pages linked to from the "Build"_Build.html doc page.
Richard Berger (Temple U) has also written a "more comprehensive
guide"_https://github.com/lammps/lammps/blob/master/cmake/README.md
for how to use CMake to build LAMMPS. If you are new to CMake it is a
good place to start.
:line
Building LAMMPS with CMake is a two-step process. First you use CMake
to create a build environment in a new directory. On Linux systems,
this will be based on makefiles for use with make. Then you use the
make command to build LAMMPS, which uses the created
Makefile(s). Example:
cd lammps # change to the LAMMPS distribution directory
mkdir build; cd build # create a new directory (folder) for build
cmake \[options ...\] ../cmake # configuration with (command-line) cmake
make # compilation :pre
The cmake command will detect available features, enable selected
packages and options, and will generate the build environment. By default
this build environment will be created for "Unix Makefiles" on most
platforms and particularly on Linux. However, alternate build tools
(e.g. Ninja) and support files for Integrated Development Environments
(IDE) like Eclipse, CodeBlocks, or Kate can be generated, too. This is
selected via the "-G" command line flag. For the rest of the documentation
we will assume that the build environment is generated for makefiles
and thus the make command will be used to compile and link LAMMPS as
indicated above, producing (by default) an executable called "lmp" and
a library called "liblammps.a" in the "build" folder. When generating
a build environment for the "Ninja" build tool, the build command would
be "ninja" instead of "make".
If your machine has multiple CPU cores (most do these days), using a
command like "make -jN" (with N being the number of available local
CPU cores) can be much faster. If you plan to do development on
LAMMPS or need to re-compile LAMMPS repeatedly, installation of the
ccache (= Compiler Cache) software may speed up repeated compilation
even more.
After compilation, you may optionally install the LAMMPS executable into
your system with:
make install # optional, copy LAMMPS executable & library elsewhere :pre
This will install the lammps executable and library (if requested), some
tools (if configured) and additional files like library API headers,
manpages, potential and force field files. The location of the installation
tree is set by the CMake variable "CMAKE_INSTALL_PREFIX" which defaults
to $\{HOME\}/.local
:line
There are 3 variants of CMake: a command-line version (cmake), a text mode
UI version (ccmake), and a graphical GUI version (cmake-GUI). You can use
any of them interchangeably to configure and create the LAMMPS build
environment. On Linux all the versions produce a Makefile as their
output. See more details on each below.
You can specify a variety of options with any of the 3 versions, which
affect how the build is performed and what is included in the LAMMPS
executable. Links to pages explaining all the options are listed on
the "Build"_Build.html doc page.
You must perform the CMake build system generation and compilation in
a new directory you create. It can be anywhere on your local machine.
In these Build pages we assume that you are building in a directory
called "lammps/build". You can perform separate builds independently
with different options, so long as you perform each of them in a
separate directory you create. All the auxiliary files created by one
build process (executable, object files, log files, etc) are stored in
this directory or sub-directories within it that CMake creates.
NOTE: To perform a CMake build, no packages can be installed or a
build been previously attempted in the LAMMPS src directory by using
"make" commands to "perform a conventional LAMMPS
build"_Build_make.html. CMake detects if this is the case and
generates an error, telling you to type "make no-all purge" in the src
directory to un-install all packages. The purge removes all the *.h
files auto-generated by make.
You must have CMake version 2.8 or later on your system to build
LAMMPS. A handful of LAMMPS packages (KOKKOS, LATTE, MSCG) require a
later version. CMake will print a message telling you if a later
version is required. Installation instructions for CMake are below.
After the initial build, if you edit LAMMPS source files, or add your
own new files to the source directory, you can just re-type make from
your build directory and it will re-compile only the files that have
changed. If you want to change CMake options you can run cmake (or
ccmake or cmake-gui) again from the same build directory and alter
various options; see details below. Or you can remove the entire build
folder, recreate the directory and start over.
:line
[Command-line version of CMake]:
cmake \[options ...\] /path/to/lammps/cmake # build from any dir
cmake \[options ...\] ../cmake # build from lammps/build :pre
The cmake command takes one required argument, which is the LAMMPS
cmake directory which contains the CMakeLists.txt file.
The argument can be preceeded or followed by various CMake
command-line options. Several useful ones are:
-D CMAKE_INSTALL_PREFIX=path # where to install LAMMPS executable/lib if desired
-D CMAKE_BUILD_TYPE=type # type = RelWithDebInfo (default), Release, MinSizeRel, or Debug
-G output # style of output CMake generates
-DVARIABLE=value # setting for a LAMMPS feature to enable
-D VARIABLE=value # ditto, but cannot come after CMakeLists.txt dir
-C path/to/preset/file # load some CMake settings before configuring :pre
All the LAMMPS-specific -D variables that a LAMMPS build supports are
described on the pages linked to from the "Build"_Build.html doc page.
All of these variable names are upper-case and their values are
lower-case, e.g. -D LAMMPS_SIZES=smallbig. For boolean values, any of
these forms can be used: yes/no, on/off, 1/0.
On Unix/Linux machines, CMake generates a Makefile by default to
perform the LAMMPS build. Alternate forms of build info can be
generated via the -G switch, e.g. Visual Studio on a Windows machine,
Xcode on MacOS, or KDevelop on Linux. Type "cmake --help" to see the
"Generator" styles of output your system supports.
NOTE: When CMake runs, it prints configuration info to the screen.
You should review this to verify all the features you requested were
enabled, including packages. You can also see what compilers and
compile options will be used for the build. Any errors in CMake
variable syntax will also be flagged, e.g. mis-typed variable names or
variable values.
CMake creates a CMakeCache.txt file when it runs. This stores all the
settings, so that when running CMake again you can use the current
folder '.' instead of the path to the LAMMPS cmake folder as the
required argument to the CMake command. Either way the existing
settings will be inherited unless the CMakeCache.txt file is removed.
If you later want to change a setting you can rerun cmake in the build
directory with different setting. Please note that some automatically
detected variables will not change their value when you rerun cmake.
In these cases it is usually better to first remove all the
files/directories in the build directory, or start with a fresh build
directory.
:line
[Curses version (terminal-style menu) of CMake]:
ccmake ../cmake :pre
You initiate the configuration and build environment generation steps
separately. For the first you have to type [c], for the second you
have to type [g]. You may need to type [c] multiple times, and may be
required to edit some of the entries of CMake configuration variables
in between. Please see the "ccmake
manual"_https://cmake.org/cmake/help/latest/manual/ccmake.1.html for
more information.
:line
[GUI version of CMake]:
cmake-gui ../cmake :pre
You initiate the configuration and build environment generation steps
separately. For the first you have to click on the [Configure] button,
for the second you have to click on the [Generate] button. You may
need to click on [Configure] multiple times, and may be required to
edit some of the entries of CMake configuration variables in between.
Please see the "cmake-gui
manual"_https://cmake.org/cmake/help/latest/manual/cmake-gui.1.html
for more information.
:line
[Installing CMake]
Check if your machine already has CMake installed:
which cmake # do you have it?
which cmake3 # version 3 may have this name
cmake --version # what specific version you have :pre
On clusters or supercomputers which use environment modules to manage
software packages, do this:
module list # is a cmake module already loaded?
module avail # is a cmake module available?
module load cmake3 # load cmake module with appropriate name :pre
Most Linux distributions offer pre-compiled cmake packages through
their package management system. If you do not have CMake or a new
enough version, you can download the latest version at
"https://cmake.org/download/"_https://cmake.org/download/.
Instructions on how to install it on various platforms can be found
"on this page"_https://cmake.org/install/.

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"Higher level section"_Build.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Development build options (CMake only) :h3
The CMake build of LAMMPS has a few extra options which are useful during
development, testing or debugging.
:line
Verify compilation flags :h4,link(compilation)
Sometimes it is necessary to verify the complete sequence of compilation flags
generated by the CMake build. To enable a more verbose output during
compilation you can use the following option.
-D CMAKE_VERBOSE_MAKEFILE=value # value = no (default) or yes :pre
Another way of doing this without reconfiguration is calling make with variable VERBOSE set to 1:
make VERBOSE=1 :pre
:line
Address, Undefined Behavior, and Thread Sanitizer Support :h4,link(sanitizer)
Compilers such as GCC and Clang support generating binaries which use different
sanitizers to detect problems in code during run-time. They can detect "memory leaks"_https://clang.llvm.org/docs/AddressSanitizer.html,
code that runs into "undefined behavior"_https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html of the
language and "data races"_https://clang.llvm.org/docs/ThreadSanitizer.html in threaded code.
The following settings allow you enable these features if your compiler supports
it. Please note that they come with a performance hit. However, they are
usually faster than using tools like Valgrind.
-D ENABLE_SANITIZE_ADDRESS=value # enable Address Sanitizer, value = no (default) or yes
-D ENABLE_SANITIZE_UNDEFINED=value # enable Undefined Behaviour Sanitizer, value = no (default) or yes
-D ENABLE_SANITIZE_THREAD=value # enable Thread Sanitizer, value = no (default) or yes
:pre
:line
Code Coverage and Testing :h4,link(testing)
We do extensive regression testing of the LAMMPS code base on a continuous
basis. Some of the logic to do this has been added to the CMake build so
developers can run the tests directly on their workstation.
NOTE: this is incomplete and only represents a small subset of tests that we run
-D ENABLE_TESTING=value # enable simple run tests of LAMMPS, value = no (default) or yes
-D LAMMPS_TESTING_SOURCE_DIR=path # path to lammps-testing repository (option if in custom location)
-D LAMMPS_TESTING_GIT_TAG=value # version of lammps-testing repository that should be used, value = master (default) or custom git commit or tag
:pre
If you enable testing in the CMake build it will create an additional target called "test". You can run them with:
make test
:pre
The test cases used come from the lammps-testing repository. They are
derivatives of the examples folder with some modifications to make the run
faster.
You can also collect code coverage metrics while running the tests by enabling
coverage support during building.
-D ENABLE_COVERAGE=value # enable coverage measurements, value = no (default) or yes :pre
This will also add the following targets to generate coverage reports after running the LAMMPS executable:
make test # run tests first!
make gen_coverage_html # generate coverage report in HTML format
make gen_coverage_xml # generate coverage report in XML format
:pre
These reports require GCOVR to be installed. The easiest way to do this to install it via pip:
pip install git+https://github.com/gcovr/gcovr.git :pre
:pre

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"Higher level section"_Build.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Link LAMMPS as a library to another code :h3
LAMMPS can be used as a library by another application, including
Python scripts. The files src/library.cpp and library.h define the
C-style API for using LAMMPS as a library. See the "Howto
library"_Howto_library.html doc page for a description of the
interface and how to extend it for your needs.
The "Build basics"_Build_basics.html doc page explains how to build
LAMMPS as either a shared or static library. This results in one of
these 2 files:
liblammps.so # shared library
liblammps.a # static library
:line
[Link with LAMMPS as a static library]:
The calling application can link to LAMMPS as a static library with a
link command like this:
g++ caller.o -L/home/sjplimp/lammps/src -llammps -o caller
The -L argument is the path to where the liblammps.a file is. The
-llammps argument is shorthand for the file liblammps.a.
:line
[Link with LAMMPS as a shared library]:
If you wish to link to liblammps.so, the operating system finds shared
libraries to load at run-time using the environment variable
LD_LIBRARY_PATH. To enable this you can do one of two things:
(1) Copy the liblammps.so file to a location the system can find it,
such as /usr/local/lib. I.e. a directory already listed in your
LD_LIBRARY_PATH variable. You can type
printenv LD_LIBRARY_PATH :pre
to see what directories are in that list.
(2) Add the LAMMPS src directory (or the directory you perform CMake
build in) to your LD_LIBRARY_PATH, so that the current version of the
shared library is always available to programs that use it.
For the csh or tcsh shells, you would add something like this to your
~/.cshrc file:
setenv LD_LIBRARY_PATH $\{LD_LIBRARY_PATH\}:/home/sjplimp/lammps/src :pre
:line
[Calling the LAMMPS library]:
Either flavor of library (static or shared) allows one or more LAMMPS
objects to be instantiated from the calling program.
When used from a C++ program, all of LAMMPS is wrapped in a LAMMPS_NS
namespace; you can safely use any of its classes and methods from
within the calling code, as needed.
When used from a C or Fortran program, the library has a simple
C-style interface, provided in src/library.cpp and src/library.h.
See the "Python library"_Python_library.html doc page for a
description of the Python interface to LAMMPS, which wraps the C-style
interface.
See the sample codes in examples/COUPLE/simple for examples of C++ and
C and Fortran codes that invoke LAMMPS through its library interface.
Other examples in the COUPLE directory use coupling ideas discussed on
the "Howto couple"_Howto_couple.html doc page.

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"Higher level section"_Build.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Build LAMMPS with make :h3
Building LAMMPS with traditional makefiles requires that you have a
Makefile."machine" file appropriate for your system in the src/MAKE,
src/MAKE/MACHINES, src/MAKE/OPTIONS, or src/MAKE/MINE directory (see
below). It can include various options for customizing your LAMMPS
build with a number of global compilation options and features.
To include LAMMPS packages (i.e. optional commands and styles) you
must install them first, as discussed on the "Build
package"_Build_package.html doc page. If the packages require
provided or external libraries, you must build those libraries before
building LAMMPS. Building "LAMMPS with CMake"_Build_cmake.html can
automate all of this for many types of machines, especially
workstations, desktops and laptops, so we suggest you try it first.
These commands perform a default LAMMPS build, producing the LAMMPS
executable lmp_serial or lmp_mpi in lammps/src:
cd lammps/src
make serial # build a serial LAMMPS executable
make mpi # build a parallel LAMMPS executable with MPI
make # see a variety of make options :pre
This initial compilation can take a long time, since LAMMPS is a large
project with many features. If your machine has multiple CPU cores
(most do these days), using a command like "make -jN mpi" (with N =
the number of available CPU cores) can be much faster. If you plan to
do development on LAMMPS or need to re-compile LAMMPS repeatedly, the
installation of the ccache (= Compiler Cache) software may speed up
compilation even more.
After the initial build, whenever you edit LAMMPS source files, or add
or remove new files to the source directory (e.g. by installing or
uninstalling packages), you must re-compile and relink the LAMMPS
executable with the same "make" command. This makefiles dependencies
should insure that only the subset of files that need to be are
re-compiled.
NOTE: When you build LAMMPS for the first time, a long list of *.d
files will be printed out rapidly. This is not an error; it is the
Makefile doing its normal creation of dependencies.
:line
The lammps/src/MAKE tree contains all the Makefile.machine files
included in the LAMMPS distribution. Typing "make machine" uses
Makefile.machine. Thus the "make serial" or "make mpi" lines above
use Makefile.serial and Makefile.mpi. Others are in these dirs:
OPTIONS # Makefiles which enable specific options
MACHINES # Makefiles for specific machines
MINE # customized Makefiles you create (you may need to create this folder) :pre
Typing "make" lists all the available Makefile.machine files. A file
with the same name can appear in multiple folders (not a good idea).
The order the dirs are searched is as follows: src/MAKE/MINE,
src/MAKE, src/MAKE/OPTIONS, src/MAKE/MACHINES. This gives preference
to a customized file you put in src/MAKE/MINE.
Makefiles you may wish to try include these (some require a package
first be installed). Many of these include specific compiler flags
for optimized performance. Please note, however, that some of these
customized machine Makefile are contributed by users. Since both
compilers, OS configurations, and LAMMPS itself keep changing, their
settings may become outdated:
make mac # build serial LAMMPS on a Mac
make mac_mpi # build parallel LAMMPS on a Mac
make intel_cpu # build with the USER-INTEL package optimized for CPUs
make knl # build with the USER-INTEL package optimized for KNLs
make opt # build with the OPT package optimized for CPUs
make omp # build with the USER-OMP package optimized for OpenMP
make kokkos_omp # build with the KOKKOS package for OpenMP
make kokkos_cuda_mpi # build with the KOKKOS package for GPUs
make kokkos_phi # build with the KOKKOS package for KNLs :pre

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"Higher level section"_Build.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Include packages in build :h3
In LAMMPS, a package is a group of files that enable a specific set of
features. For example, force fields for molecular systems or
rigid-body constraints are in packages. In the src directory, each
package is a sub-directory with the package name in capital letters.
An overview of packages is given on the "Packages"_Packages.html doc
page. Brief overviews of each package are on the "Packages
details"_Packages_details.html doc page.
When building LAMMPS, you can choose to include or exclude each
package. In general there is no need to include a package if you
never plan to use its features.
If you get a run-time error that a LAMMPS command or style is
"Unknown", it is often because the command is contained in a package,
and your build did not include that package. Running LAMMPS with the
"-h command-line switch"_Run_options.html will print all the included
packages and commands for that executable.
For the majority of packages, if you follow the single step below to
include it, you can then build LAMMPS exactly the same as you would
without any packages installed. A few packages may require additional
steps, as explained on the "Build extras"_Build_extras.html doc page.
These links take you to the extra instructions for those select
packages:
"COMPRESS"_Build_extras.html#compress,
"GPU"_Build_extras.html#gpu,
"KIM"_Build_extras.html#kim,
"KOKKOS"_Build_extras.html#kokkos,
"LATTE"_Build_extras.html#latte,
"MESSAGE"_Build_extras.html#message,
"MSCG"_Build_extras.html#mscg,
"OPT"_Build_extras.html#opt,
"POEMS"_Build_extras.html#poems,
"PYTHON"_Build_extras.html#python,
"VORONOI"_Build_extras.html#voronoi,
"USER-ADIOS"_Build_extras.html#user-adios,
"USER-ATC"_Build_extras.html#user-atc,
"USER-AWPMD"_Build_extras.html#user-awpmd,
"USER-COLVARS"_Build_extras.html#user-colvars,
"USER-H5MD"_Build_extras.html#user-h5md,
"USER-INTEL"_Build_extras.html#user-intel,
"USER-MOLFILE"_Build_extras.html#user-molfile,
"USER-NETCDF"_Build_extras.html#user-netcdf,
"USER-PLUMED"_Build_extras.html#user-plumed,
"USER-OMP"_Build_extras.html#user-omp,
"USER-QMMM"_Build_extras.html#user-qmmm,
"USER-QUIP"_Build_extras.html#user-quip,
"USER-SCAFACOS"_Build_extras.html#user-scafacos,
"USER-SMD"_Build_extras.html#user-smd,
"USER-VTK"_Build_extras.html#user-vtk :tb(c=6,ea=c,a=l)
The mechanism for including packages is simple but different for CMake
versus make.
[CMake variables]:
-D PKG_NAME=value # yes or no (default) :pre
Examples:
-D PKG_MANYBODY=yes
-D PKG_USER-INTEL=yes :pre
All standard and user packages are included the same way. Note that
USER packages have a hyphen between USER and the rest of the package
name, not an underscore.
See the shortcut section below for how to install many packages at
once with CMake.
NOTE: If you toggle back and forth between building with CMake vs
make, no packages in the src directory can be installed when you
invoke cmake. CMake will give an error if that is not the case,
indicating how you can un-install all packages in the src dir.
[Traditional make]:
cd lammps/src
make ps # check which packages are currently installed
make yes-name # install a package with name
make no-name # un-install a package with name
make mpi # build LAMMPS with whatever packages are now installed :pre
Examples:
make no-rigid
make yes-user-intel :pre
All standard and user packages are included the same way.
See the shortcut section below for how to install many packages at
once with make.
NOTE: You must always re-build LAMMPS (via make) after installing or
un-installing a package, for the action to take effect.
NOTE: You cannot install or un-install packages and build LAMMPS in a
single make command with multiple targets, e.g. make yes-colloid mpi.
This is because the make procedure creates a list of source files that
will be out-of-date for the build if the package configuration changes
within the same command. You can include or exclude multiple packages
in a single make command, e.g. make yes-colloid no-manybody.
[CMake and make info]:
Any package can be included or excluded in a LAMMPS build, independent
of all other packages. However, some packages include files derived
from files in other packages. LAMMPS checks for this and does the
right thing. Individual files are only included if their dependencies
are already included. Likewise, if a package is excluded, other files
dependent on that package are also excluded.
When you download a LAMMPS tarball or download LAMMPS source files
from the Git or SVN repositories, no packages are pre-installed in the
src directory.
NOTE: Prior to Aug 2018, if you downloaded a tarball, 3 packages
(KSPACE, MANYBODY, MOLECULE) were pre-installed in the src directory.
That is no longer the case, so that CMake will build as-is without the
need to un-install those packages.
:line
[CMake shortcuts for installing many packages]:
Instead of specifying all the CMake options via the command-line,
CMake allows initializing the variable cache using script files. These
are regular CMake files which can manipulate and set variables, and
can also contain control flow constructs.
LAMMPS includes several of these files to define configuration
"presets", similar to the options that exist for the Make based
system. Using these files you can enable/disable portions of the
available packages in LAMMPS. If you need a custom preset you can take
one of them as a starting point and customize it to your needs.
cmake -C ../cmake/presets/all_on.cmake \[OPTIONS\] ../cmake |
enable all packages |
cmake -C ../cmake/presets/all_off.cmake \[OPTIONS\] ../cmake |
disable all packages |
cmake -C ../cmake/presets/minimal.cmake \[OPTIONS\] ../cmake |
enable just a few core packages |
cmake -C ../cmake/presets/most.cmake \[OPTIONS\] ../cmake |
enable most common packages |
cmake -C ../cmake/presets/nolib.cmake \[OPTIONS\] ../cmake |
disable packages that do require extra libraries or tools |
cmake -C ../cmake/presets/clang.cmake \[OPTIONS\] ../cmake |
change settings to use the Clang compilers by default |
cmake -C ../cmake/presets/mingw.cmake \[OPTIONS\] ../cmake |
enable all packages compatible with MinGW compilers :tb(c=2,s=|,a=l)
NOTE: Running cmake this way manipulates the variable cache in your
current build directory. You can combine multiple presets and options
in a single cmake run, or change settings incrementally by running
cmake with new flags.
[Example:]
# build LAMMPS with most commonly used packages, but then remove
# those requiring additional library or tools, but still enable
# GPU package and configure it for using CUDA. You can run.
mkdir build
cd build
cmake -C ../cmake/presets/most.cmake -C ../cmake/presets/nolib.cmake -D PKG_GPU=on -D GPU_API=cuda ../cmake :pre
# to add another package, say BODY to the previous configuration you can run:
cmake -D PKG_BODY=on . :pre
# to reset the package selection from above to the default of no packages
# but leaving all other settings untouched. You can run:
cmake -C ../cmake/presets/no_all.cmake . :pre
:line
[Make shortcuts for installing many packages]:
The following commands are useful for managing package source files
and their installation when building LAMMPS via traditional make.
Just type "make" in lammps/src to see a one-line summary.
These commands install/un-install sets of packages:
make yes-all | install all packages
make no-all | un-install all packages
make yes-standard or make yes-std | install standard packages
make no-standard or make no-std| un-install standard packages
make yes-user | install user packages
make no-user | un-install user packages
make yes-lib | install packages that require extra libraries
make no-lib | un-install packages that require extra libraries
make yes-ext | install packages that require external libraries
make no-ext | un-install packages that require external libraries :tb(s=|,a=l)
which install/un-install various sets of packages. Typing "make
package" will list all the these commands.
NOTE: Installing or un-installing a package works by simply copying
files back and forth between the main src directory and
sub-directories with the package name (e.g. src/KSPACE, src/USER-ATC),
so that the files are included or excluded when LAMMPS is built.
The following make commands help manage files that exist in both the
src directory and in package sub-directories. You do not normally
need to use these commands unless you are editing LAMMPS files or are
"installing a patch"_Install_patch.html downloaded from the LAMMPS web
site.
Type "make package-status" or "make ps" to show which packages are
currently installed. For those that are installed, it will list any
files that are different in the src directory and package
sub-directory.
Type "make package-installed" or "make pi" to show which packages are
currently installed, without listing the status of packages that are
not installed.
Type "make package-update" or "make pu" to overwrite src files with
files from the package sub-directories if the package is installed.
It should be used after a "patch has been applied"_Install_patch.html,
since patches only update the files in the package sub-directory, but
not the src files.
Type "make package-overwrite" to overwrite files in the package
sub-directories with src files.
Type "make package-diff" to list all differences between pairs of
files in both the src dir and a package dir.

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"Higher level section"_Build.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Optional build settings :h3
LAMMPS can be built with several optional settings. Each sub-section
explain how to do this for building both with CMake and make.
"C++11 standard compliance test"_#cxx11 when building all of LAMMPS
"FFT library"_#fft for use with the "kspace_style pppm"_kspace_style.html command
"Size of LAMMPS data types"_#size
"Read or write compressed files"_#gzip
"Output of JPG and PNG files"_#graphics via the "dump image"_dump_image.html command
"Output of movie files"_#graphics via the "dump_movie"_dump_image.html command
"Memory allocation alignment"_#align
"Workaround for long long integers"_#longlong
"Error handling exceptions"_#exceptions when using LAMMPS as a library :all(b)
:line
C++11 standard compliance test :h4,link(cxx11)
The LAMMPS developers plan to transition to make the C++11 standard the
minimum requirement for compiling LAMMPS. Currently this only applies to
some packages like KOKKOS while the rest aims to be compatible with the C++98
standard. Most currently used compilers are compatible with C++11; some need
to set extra flags to switch. To determine the impact of requiring C++11,
we have added a simple compliance test to the source code, that will cause
the compilation to abort, if C++11 compliance is not available or enabled.
To bypass this check, you need to change a setting in the makefile or
when calling CMake.
[CMake variable]:
-D DISABLE_CXX11_REQUIREMENT=yes :pre
You can set additional C++ compiler flags (beyond those selected by CMake)
through the CMAKE_CXX_FLAGS variable. Example for CentOS 7:
-D CMAKE_CXX_FLAGS="-O3 -g -fopenmp -DNDEBUG -std=c++11" :pre
[Makefile.machine setting]:
LMP_INC = -DLAMMPS_CXX98 :pre
:line
FFT library :h4,link(fft)
When the KSPACE package is included in a LAMMPS build, the
"kspace_style pppm"_kspace_style.html command performs 3d FFTs which
require use of an FFT library to compute 1d FFTs. The KISS FFT
library is included with LAMMPS but other libraries can be faster.
LAMMPS can use them if they are available on your system.
[CMake variables]:
-D FFT=value # FFTW3 or MKL or KISS, default is FFTW3 if found, else KISS
-D FFT_SINGLE=value # yes or no (default), no = double precision
-D FFT_PACK=value # array (default) or pointer or memcpy :pre
NOTE: The values for the FFT variable must be in upper-case. This is
an exception to the rule that all CMake variables can be specified
with lower-case values.
Usually these settings are all that is needed. If CMake cannot find
the FFT library, you can set these variables:
-D FFTW3_INCLUDE_DIRS=path # path to FFTW3 include files
-D FFTW3_LIBRARIES=path # path to FFTW3 libraries
-D MKL_INCLUDE_DIRS=path # ditto for Intel MKL library
-D MKL_LIBRARIES=path :pre
[Makefile.machine settings]:
FFT_INC = -DFFT_FFTW3 # -DFFT_FFTW3, -DFFT_FFTW (same as -DFFT_FFTW3), -DFFT_MKL, or -DFFT_KISS
# default is KISS if not specified
FFT_INC = -DFFT_SINGLE # do not specify for double precision
FFT_INC = -DFFT_PACK_ARRAY # or -DFFT_PACK_POINTER or -DFFT_PACK_MEMCPY :pre
# default is FFT_PACK_ARRAY if not specified
FFT_INC = -I/usr/local/include
FFT_PATH = -L/usr/local/lib
FFT_LIB = -lfftw3 # FFTW3 double precision
FFT_LIB = -lfftw3 -lfftw3f # FFTW3 single precision
FFT_LIB = -lmkl_intel_lp64 -lmkl_sequential -lmkl_core # MKL with Intel compiler
FFT_LIB = -lmkl_gf_lp64 -lmkl_sequential -lmkl_core # MKL with GNU compier :pre
As with CMake, you do not need to set paths in FFT_INC or FFT_PATH, if
make can find the FFT header and library files. You must specify
FFT_LIB with the appropriate FFT libraries to include in the link.
[CMake and make info]:
The "KISS FFT library"_http://kissfft.sf.net is included in the LAMMPS
distribution. It is portable across all platforms. Depending on the
size of the FFTs and the number of processors used, the other
libraries listed here can be faster.
However, note that long-range Coulombics are only a portion of the
per-timestep CPU cost, FFTs are only a portion of long-range
Coulombics, and 1d FFTs are only a portion of the FFT cost (parallel
communication can be costly). A breakdown of these timings is printed
to the screen at the end of a run using the "kspace_style
pppm"_kspace_style.html command. The "Run output"_Run_output.html
doc page gives more details.
FFTW is a fast, portable FFT library that should also work on any
platform and can be faster than the KISS FFT library. You can
download it from "www.fftw.org"_http://www.fftw.org. LAMMPS requires
version 3.X; the legacy version 2.1.X is no longer supported.
Building FFTW for your box should be as simple as ./configure; make;
make install. The install command typically requires root privileges
(e.g. invoke it via sudo), unless you specify a local directory with
the "--prefix" option of configure. Type "./configure --help" to see
various options.
The Intel MKL math library is part of the Intel compiler suite. It
can be used with the Intel or GNU compiler (see FFT_LIB setting above).
Performing 3d FFTs in parallel can be time consuming due to data
access and required communication. This cost can be reduced by
performing single-precision FFTs instead of double precision. Single
precision means the real and imaginary parts of a complex datum are
4-byte floats. Double precision means they are 8-byte doubles. Note
that Fourier transform and related PPPM operations are somewhat less
sensitive to floating point truncation errors and thus the resulting
error is less than the difference in precision. Using the -DFFT_SINGLE
setting trades off a little accuracy for reduced memory use and
parallel communication costs for transposing 3d FFT data.
When using -DFFT_SINGLE with FFTW3 you may need to build the FFTW
library a second time with support for single-precision.
For FFTW3, do the following, which should produce the additional
library libfftw3f.a
make clean
./configure --enable-single; make; make install :pre
Performing 3d FFTs requires communication to transpose the 3d FFT
grid. The data packing/unpacking for this can be done in one of 3
modes (ARRAY, POINTER, MEMCPY) as set by the FFT_PACK syntax above.
Depending on the machine, the size of the FFT grid, the number of
processors used, one option may be slightly faster. The default is
ARRAY mode.
:line
Size of LAMMPS data types :h4,link(size)
LAMMPS has a few integer data types which can be defined as 4-byte or
8-byte integers. The default setting of "smallbig" is almost always
adequate.
[CMake variable]:
-D LAMMPS_SIZES=value # smallbig (default) or bigbig or smallsmall :pre
[Makefile.machine setting]:
LMP_INC = -DLAMMPS_SMALLBIG # or -DLAMMPS_BIGBIG or -DLAMMPS_SMALLSMALL :pre
# default is LAMMPS_SMALLBIG if not specified
[CMake and make info]:
The default "smallbig" setting allows for simulations with:
total atom count = 2^63 atoms (about 9e18)
total timesteps = 2^63 (about 9e18)
atom IDs = 2^31 (about 2 billion)
image flags = roll over at 512 :ul
The "bigbig" setting increases the latter two limits. It allows for:
total atom count = 2^63 atoms (about 9e18)
total timesteps = 2^63 (about 9e18)
atom IDs = 2^63 (about 9e18)
image flags = roll over at about 1 million (2^20) :ul
The "smallsmall" setting is only needed if your machine does not
support 8-byte integers. It allows for:
total atom count = 2^31 atoms (about 2 billion)
total timesteps = 2^31 (about 2 billion)
atom IDs = 2^31 (about 2 billion)
image flags = roll over at 512 (2^9) :ul
Atom IDs are not required for atomic systems which do not store bond
topology information, though IDs are enabled by default. The
"atom_modify id no"_atom_modify.html command will turn them off. Atom
IDs are required for molecular systems with bond topology (bonds,
angles, dihedrals, etc). Thus if you model a molecular system with
more than 2 billion atoms, you need the "bigbig" setting.
Image flags store 3 values per atom which count the number of times an
atom has moved through the periodic box in each dimension. See the
"dump"_dump.html doc page for a discussion. If an atom moves through
the periodic box more than this limit, the value will "roll over",
e.g. from 511 to -512, which can cause diagnostics like the
mean-squared displacement, as calculated by the "compute
msd"_compute_msd.html command, to be faulty.
Note that the USER-ATC package and the USER-INTEL package are currently
not compatible with the "bigbig" setting. Also, there are limitations
when using the library interface. Some functions with known issues
have been replaced by dummy calls printing a corresponding error rather
than crashing randomly or corrupting data.
Also note that the GPU package requires its lib/gpu library to be
compiled with the same size setting, or the link will fail. A CMake
build does this automatically. When building with make, the setting
in whichever lib/gpu/Makefile is used must be the same as above.
:line
Output of JPG, PNG, and movie files :h4,link(graphics)
The "dump image"_dump_image.html command has options to output JPEG or
PNG image files. Likewise the "dump movie"_dump_image.html command
outputs movie files in MPEG format. Using these options requires the
following settings:
[CMake variables]:
-D WITH_JPEG=value # yes or no
# default = yes if CMake finds JPEG files, else no
-D WITH_PNG=value # yes or no
# default = yes if CMake finds PNG and ZLIB files, else no
-D WITH_FFMPEG=value # yes or no
# default = yes if CMake can find ffmpeg, else no :pre
Usually these settings are all that is needed. If CMake cannot find
the graphics header, library, executable files, you can set these
variables:
-D JPEG_INCLUDE_DIR=path # path to jpeglib.h header file
-D JPEG_LIBRARIES=path # path to libjpeg.a (.so) file
-D PNG_INCLUDE_DIR=path # path to png.h header file
-D PNG_LIBRARIES=path # path to libpng.a (.so) file
-D ZLIB_INCLUDE_DIR=path # path to zlib.h header file
-D ZLIB_LIBRARIES=path # path to libz.a (.so) file
-D FFMPEG_EXECUTABLE=path # path to ffmpeg executable :pre
[Makefile.machine settings]:
LMP_INC = -DLAMMPS_JPEG
LMP_INC = -DLAMMPS_PNG
LMP_INC = -DLAMMPS_FFMPEG :pre
JPG_INC = -I/usr/local/include # path to jpeglib.h, png.h, zlib.h header files if make cannot find them
JPG_PATH = -L/usr/lib # paths to libjpeg.a, libpng.a, libz.a (.so) files if make cannot find them
JPG_LIB = -ljpeg -lpng -lz # library names :pre
As with CMake, you do not need to set JPG_INC or JPG_PATH, if make can
find the graphics header and library files. You must specify JPG_LIB
with a list of graphics libraries to include in the link. You must
insure ffmpeg is in a directory where LAMMPS can find it at runtime,
i.e. a dir in your PATH environment variable.
[CMake and make info]:
Using ffmpeg to output movie files requires that your machine
supports the "popen" function in the standard runtime library.
NOTE: On some clusters with high-speed networks, using the fork()
library calls (required by popen()) can interfere with the fast
communication library and lead to simulations using ffmpeg to hang or
crash.
:line
Read or write compressed files :h4,link(gzip)
If this option is enabled, large files can be read or written with
gzip compression by several LAMMPS commands, including
"read_data"_read_data.html, "rerun"_rerun.html, and "dump"_dump.html.
[CMake variables]:
-D WITH_GZIP=value # yes or no
# default is yes if CMake can find gzip, else no
-D GZIP_EXECUTABLE=path # path to gzip executable if CMake cannot find it :pre
[Makefile.machine setting]:
LMP_INC = -DLAMMPS_GZIP :pre
[CMake and make info]:
This option requires that your machine supports the "popen()" function
in the standard runtime library and that a gzip executable can be
found by LAMMPS during a run.
NOTE: On some clusters with high-speed networks, using the fork()
library calls (required by popen()) can interfere with the fast
communication library and lead to simulations using compressed output
or input to hang or crash. For selected operations, compressed file
I/O is also available using a compression library instead, which is
what the "COMPRESS package"_Packages_details.html#PKG-COMPRESS enables.
:line
Memory allocation alignment :h4,link(align)
This setting enables the use of the posix_memalign() call instead of
malloc() when LAMMPS allocates large chunks or memory. This can make
vector instructions on CPUs more efficient, if dynamically allocated
memory is aligned on larger-than-default byte boundaries.
On most current systems, the malloc() implementation returns
pointers that are aligned to 16-byte boundaries. Using SSE vector
instructions efficiently, however, requires memory blocks being
aligned on 64-byte boundaries.
[CMake variable]:
-D LAMMPS_MEMALIGN=value # 0, 8, 16, 32, 64 (default) :pre
Use a LAMMPS_MEMALIGN value of 0 to disable using posix_memalign()
and revert to using the malloc() C-library function instead. When
compiling LAMMPS for Windows systems, malloc() will always be used
and this setting ignored.
[Makefile.machine setting]:
LMP_INC = -DLAMMPS_MEMALIGN=value # 8, 16, 32, 64 :pre
Do not set -DLAMMPS_MEMALIGN, if you want to have memory allocated
with the malloc() function call instead. -DLAMMPS_MEMALIGN [cannot]
be used on Windows, as it does use different function calls for
allocating aligned memory, that are not compatible with how LAMMPS
manages its dynamical memory.
:line
Workaround for long long integers :h4,link(longlong)
If your system or MPI version does not recognize "long long" data
types, the following setting will be needed. It converts "long long"
to a "long" data type, which should be the desired 8-byte integer on
those systems:
[CMake variable]:
-D LAMMPS_LONGLONG_TO_LONG=value # yes or no (default) :pre
[Makefile.machine setting]:
LMP_INC = -DLAMMPS_LONGLONG_TO_LONG :pre
:line
Exception handling when using LAMMPS as a library :h4,link(exceptions)
This setting is useful when external codes drive LAMMPS as a library.
With this option enabled LAMMPS errors do not kill the caller.
Instead, the call stack is unwound and control returns to the caller,
e.g. to Python.
[CMake variable]:
-D LAMMPS_EXCEPTIONS=value # yes or no (default) :pre
[Makefile.machine setting]:
LMP_INC = -DLAMMPS_EXCEPTIONS :pre

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"Higher level section"_Build.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Notes for building LAMMPS on Windows :h3
"General remarks"_#generic
"Running Linux on Windows"_#linux
"Using GNU GCC ported to Windows"_#gnu
"Using a cross-compiler"_#cross :ul
:line
General remarks :h4,link(generic)
LAMMPS is developed and tested primarily on Linux machines. The vast
majority of HPC clusters and supercomputers today runs on Linux as well.
Thus portability to other platforms is desired, but not always achieved.
The LAMMPS developers strongly rely on LAMMPS users giving feedback and
providing assistance in resolving portability issues. This particularly
true for compiling LAMMPS on Windows, since this platform has significant
differences with some low-level functionality.
Running Linux on Windows :h4,link(linux)
So before trying to build LAMMPS on Windows, please consider if using
the pre-compiled Windows binary packages are sufficient for your needs
(as an aside, those packages themselves are build on a Linux machine
using cross-compilers). If it is necessary for your to compile LAMMPS
on a Windows machine (e.g. because it is your main desktop), please also
consider using a virtual machine software and run a Linux virtual machine,
or - if have a recently updated Windows 10 installation - consider using
the Windows subsystem for Linux, which allows to run a bash shell from
Ubuntu and from there on, you can pretty much use that shell like you
are running on an Ubuntu Linux machine (e.g. installing software via
apt-get). For more details on that, please see "this tutorial"_Howto_bash.html
Using GNU GCC ported to Windows :h4,link(gnu)
One option for compiling LAMMPS on Windows natively, that has been known
to work in the past is to install a bash shell, unix shell utilities,
perl, GNU make, and a GNU compiler ported to Windows. The Cygwin package
provides a unix/linux interface to low-level Windows functions, so LAMMPS
can be compiled on Windows. The necessary (minor) modifications to LAMMPS
are included, but may not always up-to-date for recently added functionality
and the corresponding new code. A machine makefile for using cygwin for
the old build system is provided. Using CMake for this mode of compilation
is untested and not likely to work.
When compiling for Windows do [not] set the -DLAMMPS_MEMALIGN define
in the LMP_INC makefile variable and add -lwsock32 -lpsapi to the linker
flags in LIB makefile variable. Try adding -static-libgcc or -static or
both to the linker flags when your resulting LAMMPS Windows executable
complains about missing .dll files. The CMake configuration should set
this up automatically, but is untested.
In case of problems, you are recommended to contact somebody with
experience in using cygwin. If you do come across portability problems
requiring changes to the LAMMPS source code, or figure out corrections
yourself, please report them on the lammps-users mailing list, or file
them as an issue or pull request on the LAMMPS GitHub project.
Using a cross-compiler :h4,link(cross)
If you need to provide custom LAMMPS binaries for Windows, but do not
need to do the compilation on Windows, please consider using a Linux
to Windows cross-compiler. This is how currently the Windows binary
packages are created by the LAMMPS developers. Because of that, this is
probably the currently best tested and supported way to build LAMMPS
executables for Windows. There are makefiles provided for the
traditional build system, but CMake has also been successfully tested
using the mingw32-cmake and mingw64-cmake wrappers that are bundled
with the cross-compiler environment on Fedora machines. A CMake preset
selecting all packages compatible with this cross-compilation build
is provided. You likely need to disable the GPU package unless you
download and install the contents of the pre-compiled "OpenCL ICD loader
library"_https://download.lammps.org/thirdparty/opencl-win-devel.tar.gz
into your MinGW64 cross-compiler environment. The cross-compilation
currently will only produce non-MPI serial binaries.
Please keep in mind, though, that this only applies to compiling LAMMPS.
Whether the resulting binaries do work correctly is no tested by the
LAMMPS developers. We instead rely on the feedback of the users
of these pre-compiled LAMMPS packages for Windows. We will try to resolve
issues to the best of our abilities if we become aware of them. However
this is subject to time constraints and focus on HPC platforms.
Native Visual C++ support :h4,link(native)
Support for the Visual C++ compilers is currently not available. The
CMake build system is capable of creating suitable a Visual Studio
style build environment, but the LAMMPS code itself is not fully ported
to support Visual C++. Volunteers to take on this task are welcome.

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"Previous Section"_Python_head.html - "LAMMPS WWW Site"_lws -
"LAMMPS Documentation"_ld - "LAMMPS Commands"_lc - "Next
Section"_Manual.html :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Errors :h2
These doc pages describe the errors you can encounter when using
LAMMPS. The common problems include conceptual issues. The messages
and warnings doc pages give complete lists of all the messages the
code may generate (except those generated by USER packages), with
additional details for many of them.
<!-- RST
.. toctree::
:maxdepth: 1
Errors_common
Errors_bugs
Errors_messages
Errors_warnings
END_RST -->
<!-- HTML_ONLY -->
"Common problems"_Errors_common.html
"Reporting bugs"_Errors_bugs.html
"Error messages"_Errors_messages.html
"Warning messages"_Errors_warnings.html :all(b)
<!-- END_HTML_ONLY -->

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"Higher level section"_Errors.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Reporting bugs :h3
If you are confident that you have found a bug in LAMMPS, follow these
steps.
Check the "New features and bug
fixes"_http://lammps.sandia.gov/bug.html section of the "LAMMPS WWW
site"_lws to see if the bug has already been reported or fixed or the
"Unfixed bug"_http://lammps.sandia.gov/unbug.html to see if a fix is
pending.
Check the "mailing list"_http://lammps.sandia.gov/mail.html to see if
it has been discussed before.
If not, send an email to the mailing list describing the problem with
any ideas you have as to what is causing it or where in the code the
problem might be. The developers will ask for more info if needed,
such as an input script or data files.
The most useful thing you can do to help us fix the bug is to isolate
the problem. Run it on the smallest number of atoms and fewest number
of processors and with the simplest input script that reproduces the
bug and try to identify what command or combination of commands is
causing the problem.
NOTE: this page needs to have GitHub issues info added

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"Higher level section"_Errors.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Common problems :h3
If two LAMMPS runs do not produce the exact same answer on different
machines or different numbers of processors, this is typically not a
bug. In theory you should get identical answers on any number of
processors and on any machine. In practice, numerical round-off can
cause slight differences and eventual divergence of molecular dynamics
phase space trajectories within a few 100s or few 1000s of timesteps.
However, the statistical properties of the two runs (e.g. average
energy or temperature) should still be the same.
If the "velocity"_velocity.html command is used to set initial atom
velocities, a particular atom can be assigned a different velocity
when the problem is run on a different number of processors or on
different machines. If this happens, the phase space trajectories of
the two simulations will rapidly diverge. See the discussion of the
{loop} option in the "velocity"_velocity.html command for details and
options that avoid this issue.
Similarly, the "create_atoms"_create_atoms.html command generates a
lattice of atoms. For the same physical system, the ordering and
numbering of atoms by atom ID may be different depending on the number
of processors.
Some commands use random number generators which may be setup to
produce different random number streams on each processor and hence
will produce different effects when run on different numbers of
processors. A commonly-used example is the "fix
langevin"_fix_langevin.html command for thermostatting.
A LAMMPS simulation typically has two stages, setup and run. Most
LAMMPS errors are detected at setup time; others like a bond
stretching too far may not occur until the middle of a run.
LAMMPS tries to flag errors and print informative error messages so
you can fix the problem. For most errors it will also print the last
input script command that it was processing. Of course, LAMMPS cannot
figure out your physics or numerical mistakes, like choosing too big a
timestep, specifying erroneous force field coefficients, or putting 2
atoms on top of each other! If you run into errors that LAMMPS
doesn't catch that you think it should flag, please send an email to
the "developers"_http://lammps.sandia.gov/authors.html.
If you get an error message about an invalid command in your input
script, you can determine what command is causing the problem by
looking in the log.lammps file or using the "echo command"_echo.html
to see it on the screen. If you get an error like "Invalid ...
style", with ... being fix, compute, pair, etc, it means that you
mistyped the style name or that the command is part of an optional
package which was not compiled into your executable. The list of
available styles in your executable can be listed by using "the -h
command-line swith"_Run_options.html. The installation and
compilation of optional packages is explained on the "Build
packages"_Build_package.html doc page.
For a given command, LAMMPS expects certain arguments in a specified
order. If you mess this up, LAMMPS will often flag the error, but it
may also simply read a bogus argument and assign a value that is
valid, but not what you wanted. E.g. trying to read the string "abc"
as an integer value of 0. Careful reading of the associated doc page
for the command should allow you to fix these problems. In most cases,
where LAMMPS expects to read a number, either integer or floating point,
it performs a stringent test on whether the provided input actually
is an integer or floating-point number, respectively, and reject the
input with an error message (for instance, when an integer is required,
but a floating-point number 1.0 is provided):
ERROR: Expected integer parameter instead of '1.0' in input script or data file :pre
Some commands allow for using variable references in place of numeric
constants so that the value can be evaluated and may change over the
course of a run. This is typically done with the syntax {v_name} for a
parameter, where name is the name of the variable. On the other hand,
immediate variable expansion with the syntax ${name} is performed while
reading the input and before parsing commands,
NOTE: Using a variable reference (i.e. {v_name}) is only allowed if
the documentation of the corresponding command explicitly says it is.
Otherwise, you will receive an error message of this kind:
ERROR: Expected floating point parameter instead of 'v_name' in input script or data file :pre
Generally, LAMMPS will print a message to the screen and logfile and
exit gracefully when it encounters a fatal error. Sometimes it will
print a WARNING to the screen and logfile and continue on; you can
decide if the WARNING is important or not. A WARNING message that is
generated in the middle of a run is only printed to the screen, not to
the logfile, to avoid cluttering up thermodynamic output. If LAMMPS
crashes or hangs without spitting out an error message first then it
could be a bug (see "this section"_Errors_bugs.html) or one of the following
cases:
LAMMPS runs in the available memory a processor allows to be
allocated. Most reasonable MD runs are compute limited, not memory
limited, so this shouldn't be a bottleneck on most platforms. Almost
all large memory allocations in the code are done via C-style malloc's
which will generate an error message if you run out of memory.
Smaller chunks of memory are allocated via C++ "new" statements. If
you are unlucky you could run out of memory just when one of these
small requests is made, in which case the code will crash or hang (in
parallel), since LAMMPS doesn't trap on those errors.
Illegal arithmetic can cause LAMMPS to run slow or crash. This is
typically due to invalid physics and numerics that your simulation is
computing. If you see wild thermodynamic values or NaN values in your
LAMMPS output, something is wrong with your simulation. If you
suspect this is happening, it is a good idea to print out
thermodynamic info frequently (e.g. every timestep) via the
"thermo"_thermo.html so you can monitor what is happening.
Visualizing the atom movement is also a good idea to insure your model
is behaving as you expect.
In parallel, one way LAMMPS can hang is due to how different MPI
implementations handle buffering of messages. If the code hangs
without an error message, it may be that you need to specify an MPI
setting or two (usually via an environment variable) to enable
buffering or boost the sizes of messages that can be buffered.

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"Previous Section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc - "Next
Section"_Tools.html :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Example scripts :h3
The LAMMPS distribution includes an examples sub-directory with many
sample problems. Many are 2d models that run quickly and are
straightforward to visualize, requiring at most a couple of minutes to
run on a desktop machine. Each problem has an input script (in.*) and
produces a log file (log.*) when it runs. Some use a data file
(data.*) of initial coordinates as additional input. A few sample log
file run on different machines and different numbers of processors are
included in the directories to compare your answers to. E.g. a log
file like log.date.crack.foo.P means the "crack" example was run on P
processors of machine "foo" on that date (i.e. with that version of
LAMMPS).
Many of the input files have commented-out lines for creating dump
files and image files.
If you uncomment the "dump"_dump.html command in the input script, a
text dump file will be produced, which can be animated by various
"visualization programs"_http://lammps.sandia.gov/viz.html.
If you uncomment the "dump image"_dump.html command in the input
script, and assuming you have built LAMMPS with a JPG library, JPG
snapshot images will be produced when the simulation runs. They can
be quickly post-processed into a movie using commands described on the
"dump image"_dump_image.html doc page.
Animations of many of the examples can be viewed on the Movies section
of the "LAMMPS web site"_lws.
There are two kinds of sub-directories in the examples dir. Lowercase
dirs contain one or a few simple, quick-to-run problems. Uppercase
dirs contain up to several complex scripts that illustrate a
particular kind of simulation method or model. Some of these run for
longer times, e.g. to measure a particular quantity.
Lists of both kinds of directories are given below.
:line
Lowercase directories :h4
accelerate: run with various acceleration options (OpenMP, GPU, Phi)
airebo: polyethylene with AIREBO potential
atm: Axilrod-Teller-Muto potential example
balance: dynamic load balancing, 2d system
body: body particles, 2d system
cmap: CMAP 5-body contributions to CHARMM force field
colloid: big colloid particles in a small particle solvent, 2d system
comb: models using the COMB potential
controller: use of fix controller as a thermostat
coreshell: core/shell model using CORESHELL package
crack: crack propagation in a 2d solid
deposit: deposit atoms and molecules on a surface
dipole: point dipolar particles, 2d system
dreiding: methanol via Dreiding FF
eim: NaCl using the EIM potential
ellipse: ellipsoidal particles in spherical solvent, 2d system
flow: Couette and Poiseuille flow in a 2d channel
friction: frictional contact of spherical asperities between 2d surfaces
gcmc: Grand Canonical Monte Carlo (GCMC) via the fix gcmc command
granregion: use of fix wall/region/gran as boundary on granular particles
hugoniostat: Hugoniostat shock dynamics
hyper: global and local hyperdynamics of diffusion on Pt surface
indent: spherical indenter into a 2d solid
kim: use of potentials from the "OpenKIM Repository"_openkim
latte: examples for using fix latte for DFTB via the LATTE library
meam: MEAM test for SiC and shear (same as shear examples)
melt: rapid melt of 3d LJ system
message: demos for LAMMPS client/server coupling with the MESSAGE package
micelle: self-assembly of small lipid-like molecules into 2d bilayers
min: energy minimization of 2d LJ melt
mscg: parameterize a multi-scale coarse-graining (MSCG) model
msst: MSST shock dynamics
nb3b: use of non-bonded 3-body harmonic pair style
neb: nudged elastic band (NEB) calculation for barrier finding
nemd: non-equilibrium MD of 2d sheared system
obstacle: flow around two voids in a 2d channel
peptide: dynamics of a small solvated peptide chain (5-mer)
peri: Peridynamic model of cylinder impacted by indenter
pour: pouring of granular particles into a 3d box, then chute flow
prd: parallel replica dynamics of vacancy diffusion in bulk Si
python: using embedded Python in a LAMMPS input script
qeq: use of the QEQ package for charge equilibration
rdf-adf: computing radial and angle distribution functions for water
reax: RDX and TATB models using the ReaxFF
rerun: use of rerun and read_dump commands
rigid: rigid bodies modeled as independent or coupled
shear: sideways shear applied to 2d solid, with and without a void
snap: NVE dynamics for BCC tantalum crystal using SNAP potential
srd: stochastic rotation dynamics (SRD) particles as solvent
streitz: use of Streitz/Mintmire potential with charge equilibration
tad: temperature-accelerated dynamics of vacancy diffusion in bulk Si
threebody: regression test input for a variety of manybody potentials
vashishta: use of the Vashishta potential
voronoi: Voronoi tesselation via compute voronoi/atom command :tb(s=:)
Here is how you can run and visualize one of the sample problems:
cd indent
cp ../../src/lmp_linux . # copy LAMMPS executable to this dir
lmp_linux -in in.indent # run the problem :pre
Running the simulation produces the files {dump.indent} and
{log.lammps}. You can visualize the dump file of snapshots with a
variety of 3rd-party tools highlighted on the
"Visualization"_http://lammps.sandia.gov/viz.html page of the LAMMPS
web site.
If you uncomment the "dump image"_dump_image.html line(s) in the input
script a series of JPG images will be produced by the run (assuming
you built LAMMPS with JPG support; see the
"Build_settings"_Build_settings.html doc page for details). These can
be viewed individually or turned into a movie or animated by tools
like ImageMagick or QuickTime or various Windows-based tools. See the
"dump image"_dump_image.html doc page for more details. E.g. this
Imagemagick command would create a GIF file suitable for viewing in a
browser.
% convert -loop 1 *.jpg foo.gif :pre
:line
Uppercase directories :h4
ASPHERE: various aspherical particle models, using ellipsoids, rigid bodies, line/triangle particles, etc
COUPLE: examples of how to use LAMMPS as a library
DIFFUSE: compute diffusion coefficients via several methods
ELASTIC: compute elastic constants at zero temperature
ELASTIC_T: compute elastic constants at finite temperature
HEAT: compute thermal conductivity for LJ and water via fix ehex
KAPPA: compute thermal conductivity via several methods
MC: using LAMMPS in a Monte Carlo mode to relax the energy of a system
SPIN: examples for features of the SPIN package
UNITS: examples that run the same simulation in lj, real, metal units
USER: examples for USER packages and USER-contributed commands
VISCOSITY: compute viscosity via several methods :tb(s=:)
Nearly all of these directories have README files which give more
details on how to understand and use their contents.
The USER directory has a large number of sub-directories which
correspond by name to a USER package. They contain scripts that
illustrate how to use the command(s) provided in that package. Many
of the sub-directories have their own README files which give further
instructions. See the "Packages_details"_Packages_details.html doc
page for more info on specific USER packages.
:link(openkim,https://openkim.org)

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"Previous Section"_Performance.html - "LAMMPS WWW Site"_lws -
"LAMMPS Documentation"_ld - "LAMMPS Commands"_lc - "Next
Section"_Examples.html :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands.html#comm)
:line
Howto discussions :h2
These doc pages describe how to perform various tasks with LAMMPS,
both for users and developers. The
"glossary"_http://lammps.sandia.gov website page also lists MD
terminology with links to corresponding LAMMPS manual pages. The
example input scripts included in the examples dir of the LAMMPS
distribution and highlighted on the "Examples"_Examples.html doc page
also show how to setup and run various kinds of simulations.
Tutorials howto :h3
<!-- RST
.. toctree::
:name: tutorials
:maxdepth: 1
Howto_github
Howto_pylammps
Howto_bash
END_RST -->
<!-- HTML_ONLY -->
"Using GitHub with LAMMPS"_Howto_github.html
"PyLAMMPS interface to LAMMPS"_Howto_pylammps.html
"Using LAMMPS with bash on Windows"_Howto_bash.html :all(b)
<!-- END_HTML_ONLY -->
General howto :h3
<!-- RST
.. toctree::
:name: general_howto
:maxdepth: 1
Howto_restart
Howto_viz
Howto_multiple
Howto_replica
Howto_library
Howto_couple
Howto_client_server
END_RST -->
<!-- HTML_ONLY -->
"Restart a simulation"_Howto_restart.html
"Visualize LAMMPS snapshots"_Howto_viz.html
"Run multiple simulations from one input script"_Howto_multiple.html
"Multi-replica simulations"_Howto_replica.html
"Library interface to LAMMPS"_Howto_library.html
"Couple LAMMPS to other codes"_Howto_couple.html
"Using LAMMPS in client/server mode"_Howto_client_server.html :all(b)
<!-- END_HTML_ONLY -->
Settings howto :h3
<!-- RST
.. toctree::
:name: settings
:maxdepth: 1
Howto_2d
Howto_triclinic
Howto_thermostat
Howto_barostat
Howto_walls
Howto_nemd
Howto_dispersion
END_RST -->
<!-- HTML_ONLY -->
"2d simulations"_Howto_2d.html
"Triclinic (non-orthogonal) simulation boxes"_Howto_triclinic.html
"Thermostats"_Howto_thermostat.html
"Barostats"_Howto_barostat.html
"Walls"_Howto_walls.html
"NEMD simulations"_Howto_nemd.html
"Long-range dispersion settings"_Howto_dispersion.html :all(b)
<!-- END_HTML_ONLY -->
Analysis howto :h3
<!-- RST
.. toctree::
:name: analysis
:maxdepth: 1
Howto_output
Howto_chunk
Howto_temperature
Howto_elastic
Howto_kappa
Howto_viscosity
Howto_diffusion
END_RST -->
<!-- HTML_ONLY -->
"Output from LAMMPS (thermo, dumps, computes, fixes, variables)"_Howto_output.html
"Use chunks to calculate system properties"_Howto_chunk.html :all(b)
"Calculate temperature"_Howto_temperature.html
"Calculate elastic constants"_Howto_elastic.html
"Calculate thermal conductivity"_Howto_kappa.html
"Calculate viscosity"_Howto_viscosity.html
"Calculate a diffusion coefficient"_Howto_diffusion.html :all(b)
<!-- END_HTML_ONLY -->
Force fields howto :h3
<!-- RST
.. toctree::
:name: force
:maxdepth: 1
Howto_bioFF
Howto_tip3p
Howto_tip4p
Howto_spc
END_RST -->
<!-- HTML_ONLY -->
"CHARMM, AMBER, COMPASS, and DREIDING force fields"_Howto_bioFF.html
"TIP3P water model"_Howto_tip3p.html
"TIP4P water model"_Howto_tip4p.html
"SPC water model"_Howto_spc.html :all(b)
<!-- END_HTML_ONLY -->
Packages howto :h3
<!-- RST
.. toctree::
:name: packages
:maxdepth: 1
Howto_spherical
Howto_granular
Howto_body
Howto_polarizable
Howto_coreshell
Howto_drude
Howto_drude2
Howto_manifold
Howto_spins
END_RST -->
<!-- HTML_ONLY -->
"Finite-size spherical and aspherical particles"_Howto_spherical.html
"Granular models"_Howto_granular.html
"Body style particles"_Howto_body.html
"Polarizable models"_Howto_polarizable.html
"Adiabatic core/shell model"_Howto_coreshell.html
"Drude induced dipoles"_Howto_drude.html
"Drude induced dipoles (extended)"_Howto_drude2.html
"Manifolds (surfaces)"_Howto_manifold.html
"Magnetic spins"_Howto_spins.html :all(b)
<!-- END_HTML_ONLY -->

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
2d simulations :h3
Use the "dimension"_dimension.html command to specify a 2d simulation.
Make the simulation box periodic in z via the "boundary"_boundary.html
command. This is the default.
If using the "create box"_create_box.html command to define a
simulation box, set the z dimensions narrow, but finite, so that the
create_atoms command will tile the 3d simulation box with a single z
plane of atoms - e.g.
"create box"_create_box.html 1 -10 10 -10 10 -0.25 0.25 :pre
If using the "read data"_read_data.html command to read in a file of
atom coordinates, set the "zlo zhi" values to be finite but narrow,
similar to the create_box command settings just described. For each
atom in the file, assign a z coordinate so it falls inside the
z-boundaries of the box - e.g. 0.0.
Use the "fix enforce2d"_fix_enforce2d.html command as the last
defined fix to insure that the z-components of velocities and forces
are zeroed out every timestep. The reason to make it the last fix is
so that any forces induced by other fixes will be zeroed out.
Many of the example input scripts included in the LAMMPS distribution
are for 2d models.
NOTE: Some models in LAMMPS treat particles as finite-size spheres, as
opposed to point particles. See the "atom_style
sphere"_atom_style.html and "fix nve/sphere"_fix_nve_sphere.html
commands for details. By default, for 2d simulations, such particles
will still be modeled as 3d spheres, not 2d discs (circles), meaning
their moment of inertia will be that of a sphere. If you wish to
model them as 2d discs, see the "set density/disc"_set.html command
and the {disc} option for the "fix nve/sphere"_fix_nve_sphere.html,
"fix nvt/sphere"_fix_nvt_sphere.html, "fix
nph/sphere"_fix_nph_sphere.html, "fix npt/sphere"_fix_npt_sphere.html
commands.

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Barostats :h3
Barostatting means controlling the pressure in an MD simulation.
"Thermostatting"_Howto_thermostat.html means controlling the
temperature of the particles. Since the pressure includes a kinetic
component due to particle velocities, both these operations require
calculation of the temperature. Typically a target temperature (T)
and/or pressure (P) is specified by the user, and the thermostat or
barostat attempts to equilibrate the system to the requested T and/or
P.
Barostatting in LAMMPS is performed by "fixes"_fix.html. Two
barostatting methods are currently available: Nose-Hoover (npt and
nph) and Berendsen:
"fix npt"_fix_nh.html
"fix npt/sphere"_fix_npt_sphere.html
"fix npt/asphere"_fix_npt_asphere.html
"fix nph"_fix_nh.html
"fix press/berendsen"_fix_press_berendsen.html :ul
The "fix npt"_fix_nh.html commands include a Nose-Hoover thermostat
and barostat. "Fix nph"_fix_nh.html is just a Nose/Hoover barostat;
it does no thermostatting. Both "fix nph"_fix_nh.html and "fix
press/berendsen"_fix_press_berendsen.html can be used in conjunction
with any of the thermostatting fixes.
As with the "thermostats"_Howto_thermostat.html, "fix npt"_fix_nh.html
and "fix nph"_fix_nh.html only use translational motion of the
particles in computing T and P and performing thermo/barostatting.
"Fix npt/sphere"_fix_npt_sphere.html and "fix
npt/asphere"_fix_npt_asphere.html thermo/barostat using not only
translation velocities but also rotational velocities for spherical
and aspherical particles.
All of the barostatting fixes use the "compute
pressure"_compute_pressure.html compute to calculate a current
pressure. By default, this compute is created with a simple "compute
temp"_compute_temp.html (see the last argument of the "compute
pressure"_compute_pressure.html command), which is used to calculated
the kinetic component of the pressure. The barostatting fixes can
also use temperature computes that remove bias for the purpose of
computing the kinetic component which contributes to the current
pressure. See the doc pages for the individual fixes and for the
"fix_modify"_fix_modify.html command for instructions on how to assign
a temperature or pressure compute to a barostatting fix.
NOTE: As with the thermostats, the Nose/Hoover methods ("fix
npt"_fix_nh.html and "fix nph"_fix_nh.html) perform time integration.
"Fix press/berendsen"_fix_press_berendsen.html does NOT, so it should
be used with one of the constant NVE fixes or with one of the NVT
fixes.
Thermodynamic output, which can be setup via the
"thermo_style"_thermo_style.html command, often includes pressure
values. As explained on the doc page for the
"thermo_style"_thermo_style.html command, the default pressure is
setup by the thermo command itself. It is NOT the pressure associated
with any barostatting fix you have defined or with any compute you
have defined that calculates a pressure. The doc pages for the
barostatting fixes explain the ID of the pressure compute they create.
Thus if you want to view these pressures, you need to specify them
explicitly via the "thermo_style custom"_thermo_style.html command.
Or you can use the "thermo_modify"_thermo_modify.html command to
re-define what pressure compute is used for default thermodynamic
output.

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
CHARMM, AMBER, COMPASS, and DREIDING force fields :h3
A force field has 2 parts: the formulas that define it and the
coefficients used for a particular system. Here we only discuss
formulas implemented in LAMMPS that correspond to formulas commonly
used in the CHARMM, AMBER, COMPASS, and DREIDING force fields. Setting
coefficients is done either from special sections in an input data file
via the "read_data"_read_data.html command or in the input script with
commands like "pair_coeff"_pair_coeff.html or
"bond_coeff"_bond_coeff.html and so on. See the "Tools"_Tools.html doc
page for additional tools that can use CHARMM, AMBER, or Materials
Studio generated files to assign force field coefficients and convert
their output into LAMMPS input.
See "(MacKerell)"_#howto-MacKerell for a description of the CHARMM force
field. See "(Cornell)"_#howto-Cornell for a description of the AMBER
force field. See "(Sun)"_#howto-Sun for a description of the COMPASS
force field.
:link(charmm,http://www.scripps.edu/brooks)
:link(amber,http://amber.scripps.edu)
The interaction styles listed below compute force field formulas that
are consistent with common options in CHARMM or AMBER. See each
command's documentation for the formula it computes.
"bond_style"_bond_harmonic.html harmonic
"angle_style"_angle_charmm.html charmm
"dihedral_style"_dihedral_charmm.html charmmfsh
"dihedral_style"_dihedral_charmm.html charmm
"pair_style"_pair_charmm.html lj/charmmfsw/coul/charmmfsh
"pair_style"_pair_charmm.html lj/charmmfsw/coul/long
"pair_style"_pair_charmm.html lj/charmm/coul/charmm
"pair_style"_pair_charmm.html lj/charmm/coul/charmm/implicit
"pair_style"_pair_charmm.html lj/charmm/coul/long :ul
"special_bonds"_special_bonds.html charmm
"special_bonds"_special_bonds.html amber :ul
NOTE: For CHARMM, newer {charmmfsw} or {charmmfsh} styles were released
in March 2017. We recommend they be used instead of the older {charmm}
styles. See discussion of the differences on the "pair
charmm"_pair_charmm.html and "dihedral charmm"_dihedral_charmm.html doc
pages.
COMPASS is a general force field for atomistic simulation of common
organic molecules, inorganic small molecules, and polymers which was
developed using ab initio and empirical parameterization techniques.
See the "Tools"_Tools.html doc page for the msi2lmp tool for creating
LAMMPS template input and data files from BIOVIA's Materials Studio
files. Please note that the msi2lmp tool is very old and largely
unmaintained, so it does not support all features of Materials Studio
provided force field files, especially additions during the last decade.
You should watch the output carefully and compare results, where
possible. See "(Sun)"_#howto-Sun for a description of the COMPASS force
field.
These interaction styles listed below compute force field formulas that
are consistent with the COMPASS force field. See each command's
documentation for the formula it computes.
"bond_style"_bond_class2.html class2
"angle_style"_angle_class2.html class2
"dihedral_style"_dihedral_class2.html class2
"improper_style"_improper_class2.html class2 :ul
"pair_style"_pair_class2.html lj/class2
"pair_style"_pair_class2.html lj/class2/coul/cut
"pair_style"_pair_class2.html lj/class2/coul/long :ul
"special_bonds"_special_bonds.html lj/coul 0 0 1 :ul
DREIDING is a generic force field developed by the "Goddard
group"_http://www.wag.caltech.edu at Caltech and is useful for
predicting structures and dynamics of organic, biological and main-group
inorganic molecules. The philosophy in DREIDING is to use general force
constants and geometry parameters based on simple hybridization
considerations, rather than individual force constants and geometric
parameters that depend on the particular combinations of atoms involved
in the bond, angle, or torsion terms. DREIDING has an "explicit hydrogen
bond term"_pair_hbond_dreiding.html to describe interactions involving a
hydrogen atom on very electronegative atoms (N, O, F).
See "(Mayo)"_#howto-Mayo for a description of the DREIDING force field
The interaction styles listed below compute force field formulas that
are consistent with the DREIDING force field. See each command's
documentation for the formula it computes.
"bond_style"_bond_harmonic.html harmonic
"bond_style"_bond_morse.html morse :ul
"angle_style"_angle_harmonic.html harmonic
"angle_style"_angle_cosine.html cosine
"angle_style"_angle_cosine_periodic.html cosine/periodic :ul
"dihedral_style"_dihedral_charmm.html charmm
"improper_style"_improper_umbrella.html umbrella :ul
"pair_style"_pair_buck.html buck
"pair_style"_pair_buck.html buck/coul/cut
"pair_style"_pair_buck.html buck/coul/long
"pair_style"_pair_lj.html lj/cut
"pair_style"_pair_lj.html lj/cut/coul/cut
"pair_style"_pair_lj.html lj/cut/coul/long :ul
"pair_style"_pair_hbond_dreiding.html hbond/dreiding/lj
"pair_style"_pair_hbond_dreiding.html hbond/dreiding/morse :ul
"special_bonds"_special_bonds.html dreiding :ul
:line
:link(howto-MacKerell)
[(MacKerell)] MacKerell, Bashford, Bellott, Dunbrack, Evanseck, Field,
Fischer, Gao, Guo, Ha, et al, J Phys Chem, 102, 3586 (1998).
:link(howto-Cornell)
[(Cornell)] Cornell, Cieplak, Bayly, Gould, Merz, Ferguson,
Spellmeyer, Fox, Caldwell, Kollman, JACS 117, 5179-5197 (1995).
:link(howto-Sun)
[(Sun)] Sun, J. Phys. Chem. B, 102, 7338-7364 (1998).
:link(howto-Mayo)
[(Mayo)] Mayo, Olfason, Goddard III, J Phys Chem, 94, 8897-8909
(1990).

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Body particles :h3
[Overview:]
In LAMMPS, body particles are generalized finite-size particles.
Individual body particles can represent complex entities, such as
surface meshes of discrete points, collections of sub-particles,
deformable objects, etc. Note that other kinds of finite-size
spherical and aspherical particles are also supported by LAMMPS, such
as spheres, ellipsoids, line segments, and triangles, but they are
simpler entities that body particles. See the "Howto
spherical"_Howto_spherical.html doc page for a general overview of all
these particle types.
Body particles are used via the "atom_style body"_atom_style.html
command. It takes a body style as an argument. The current body
styles supported by LAMMPS are as follows. The name in the first
column is used as the {bstyle} argument for the "atom_style
body"_atom_style.html command.
{nparticle} : rigid body with N sub-particles
{rounded/polygon} : 2d polygons with N vertices
{rounded/polyhedron} : 3d polyhedra with N vertices, E edges and F faces :tb(s=:)
The body style determines what attributes are stored for each body and
thus how they can be used to compute pairwise body/body or
bond/non-body (point particle) interactions. More details of each
style are described below.
More styles may be added in the future. See the "Modify
body"_Modify_body.html doc page for details on how to add a new body
style to the code.
:line
[When to use body particles:]
You should not use body particles to model a rigid body made of
simpler particles (e.g. point, sphere, ellipsoid, line segment,
triangular particles), if the interaction between pairs of rigid
bodies is just the summation of pairwise interactions between the
simpler particles. LAMMPS already supports this kind of model via the
"fix rigid"_fix_rigid.html command. Any of the numerous pair styles
that compute interactions between simpler particles can be used. The
"fix rigid"_fix_rigid.html command time integrates the motion of the
rigid bodies. All of the standard LAMMPS commands for thermostatting,
adding constraints, performing output, etc will operate as expected on
the simple particles.
By contrast, when body particles are used, LAMMPS treats an entire
body as a single particle for purposes of computing pairwise
interactions, building neighbor lists, migrating particles between
processors, output of particles to a dump file, etc. This means that
interactions between pairs of bodies or between a body and non-body
(point) particle need to be encoded in an appropriate pair style. If
such a pair style were to mimic the "fix rigid"_fix_rigid.html model,
it would need to loop over the entire collection of interactions
between pairs of simple particles within the two bodies, each time a
single body/body interaction was computed.
Thus it only makes sense to use body particles and develop such a pair
style, when particle/particle interactions are more complex than what
the "fix rigid"_fix_rigid.html command can already calculate. For
example, consider particles with one or more of the following
attributes:
represented by a surface mesh
represented by a collection of geometric entities (e.g. planes + spheres)
deformable
internal stress that induces fragmentation :ul
For these models, the interaction between pairs of particles is likely
to be more complex than the summation of simple pairwise interactions.
An example is contact or frictional forces between particles with
planar surfaces that inter-penetrate. Likewise, the body particle may
store internal state, such as a stress tensor used to compute a
fracture criterion.
These are additional LAMMPS commands that can be used with body
particles of different styles
"fix nve/body"_fix_nve_body.html : integrate motion of a body particle in NVE ensemble
"fix nvt/body"_fix_nvt_body.html : ditto for NVT ensemble
"fix npt/body"_fix_npt_body.html : ditto for NPT ensemble
"fix nph/body"_fix_nph_body.html : ditto for NPH ensemble
"compute body/local"_compute_body_local.html : store sub-particle attributes of a body particle
"compute temp/body"_compute_temp_body.html : compute temperature of body particles
"dump local"_dump.html : output sub-particle attributes of a body particle
"dump image"_dump_image.html : output body particle attributes as an image :tb(s=:)
The pair styles defined for use with specific body styles are listed
in the sections below.
:line
[Specifics of body style nparticle:]
The {nparticle} body style represents body particles as a rigid body
with a variable number N of sub-particles. It is provided as a
vanilla, prototypical example of a body particle, although as
mentioned above, the "fix rigid"_fix_rigid.html command already
duplicates its functionality.
The atom_style body command for this body style takes two additional
arguments:
atom_style body nparticle Nmin Nmax
Nmin = minimum # of sub-particles in any body in the system
Nmax = maximum # of sub-particles in any body in the system :pre
The Nmin and Nmax arguments are used to bound the size of data
structures used internally by each particle.
When the "read_data"_read_data.html command reads a data file for this
body style, the following information must be provided for each entry
in the {Bodies} section of the data file:
atom-ID 1 M
N
ixx iyy izz ixy ixz iyz
x1 y1 z1
...
xN yN zN :pre
where M = 6 + 3*N, and N is the number of sub-particles in the body
particle.
The integer line has a single value N. The floating point line(s)
list 6 moments of inertia followed by the coordinates of the N
sub-particles (x1 to zN) as 3N values. These values can be listed on
as many lines as you wish; see the "read_data"_read_data.html command
for more details.
The 6 moments of inertia (ixx,iyy,izz,ixy,ixz,iyz) should be the
values consistent with the current orientation of the rigid body
around its center of mass. The values are with respect to the
simulation box XYZ axes, not with respect to the principal axes of the
rigid body itself. LAMMPS performs the latter calculation internally.
The coordinates of each sub-particle are specified as its x,y,z
displacement from the center-of-mass of the body particle. The
center-of-mass position of the particle is specified by the x,y,z
values in the {Atoms} section of the data file, as is the total mass
of the body particle.
The "pair_style body/nparticle"_pair_body_nparticle.html command can be used
with this body style to compute body/body and body/non-body interactions.
For output purposes via the "compute
body/local"_compute_body_local.html and "dump local"_dump.html
commands, this body style produces one datum for each of the N
sub-particles in a body particle. The datum has 3 values:
1 = x position of sub-particle
2 = y position of sub-particle
3 = z position of sub-particle :pre
These values are the current position of the sub-particle within the
simulation domain, not a displacement from the center-of-mass (COM) of
the body particle itself. These values are calculated using the
current COM and orientation of the body particle.
For images created by the "dump image"_dump_image.html command, if the
{body} keyword is set, then each body particle is drawn as a
collection of spheres, one for each sub-particle. The size of each
sphere is determined by the {bflag1} parameter for the {body} keyword.
The {bflag2} argument is ignored.
:line
[Specifics of body style rounded/polygon:]
The {rounded/polygon} body style represents body particles as a 2d
polygon with a variable number of N vertices. This style can only be
used for 2d models; see the "boundary"_boundary.html command. See the
"pair_style body/rounded/polygon" doc page for a diagram of two
squares with rounded circles at the vertices. Special cases for N = 1
(circle) and N = 2 (rod with rounded ends) can also be specified.
One use of this body style is for 2d discrete element models, as
described in "Fraige"_#body-Fraige.
Similar to body style {nparticle}, the atom_style body command for
this body style takes two additional arguments:
atom_style body rounded/polygon Nmin Nmax
Nmin = minimum # of vertices in any body in the system
Nmax = maximum # of vertices in any body in the system :pre
The Nmin and Nmax arguments are used to bound the size of data
structures used internally by each particle.
When the "read_data"_read_data.html command reads a data file for this
body style, the following information must be provided for each entry
in the {Bodies} section of the data file:
atom-ID 1 M
N
ixx iyy izz ixy ixz iyz
x1 y1 z1
...
xN yN zN
i j j k k ...
diameter :pre
where M = 6 + 3*N + 2*N + 1, and N is the number of vertices in the
body particle.
The integer line has a single value N. The floating point line(s)
list 6 moments of inertia followed by the coordinates of the N
vertices (x1 to zN) as 3N values (with z = 0.0 for each), followed by
2N vertex indices corresponding to the end points of the N edges,
followed by a single diameter value = the rounded diameter of the
circle that surrounds each vertex. The diameter value can be different
for each body particle. These floating-point values can be listed on
as many lines as you wish; see the "read_data"_read_data.html command
for more details.
The 6 moments of inertia (ixx,iyy,izz,ixy,ixz,iyz) should be the
values consistent with the current orientation of the rigid body
around its center of mass. The values are with respect to the
simulation box XYZ axes, not with respect to the principal axes of the
rigid body itself. LAMMPS performs the latter calculation internally.
The coordinates of each vertex are specified as its x,y,z displacement
from the center-of-mass of the body particle. The center-of-mass
position of the particle is specified by the x,y,z values in the
{Atoms} section of the data file.
For example, the following information would specify a square particle
whose edge length is sqrt(2) and rounded diameter is 1.0. The
orientation of the square is aligned with the xy coordinate axes which
is consistent with the 6 moments of inertia: ixx iyy izz ixy ixz iyz =
1 1 4 0 0 0. Note that only Izz matters in 2D simulations.
3 1 27
4
1 1 4 0 0 0
-0.7071 -0.7071 0
-0.7071 0.7071 0
0.7071 0.7071 0
0.7071 -0.7071 0
0 1
1 2
2 3
3 0
1.0 :pre
A rod in 2D, whose length is 4.0, mass 1.0, rounded at two ends
by circles of diameter 0.5, is specified as follows:
1 1 13
2
1 1 1.33333 0 0 0
-2 0 0
2 0 0
0.5 :pre
A disk, whose diameter is 3.0, mass 1.0, is specified as follows:
1 1 10
1
1 1 4.5 0 0 0
0 0 0
3.0 :pre
The "pair_style body/rounded/polygon"_pair_body_rounded_polygon.html
command can be used with this body style to compute body/body
interactions. The "fix wall/body/polygon"_fix_wall_body_polygon.html
command can be used with this body style to compute the interaction of
body particles with a wall.
:line
[Specifics of body style rounded/polyhedron:]
The {rounded/polyhedron} body style represents body particles as a 3d
polyhedron with a variable number of N vertices, E edges and F faces.
This style can only be used for 3d models; see the
"boundary"_boundary.html command. See the "pair_style
body/rounded/polygon" doc page for a diagram of a two 2d squares with
rounded circles at the vertices. A 3d cube with rounded spheres at
the 8 vertices and 12 rounded edges would be similar. Special cases
for N = 1 (sphere) and N = 2 (rod with rounded ends) can also be
specified.
This body style is for 3d discrete element models, as described in
"Wang"_#body-Wang.
Similar to body style {rounded/polygon}, the atom_style body command
for this body style takes two additional arguments:
atom_style body rounded/polyhedron Nmin Nmax
Nmin = minimum # of vertices in any body in the system
Nmax = maximum # of vertices in any body in the system :pre
The Nmin and Nmax arguments are used to bound the size of data
structures used internally by each particle.
When the "read_data"_read_data.html command reads a data file for this
body style, the following information must be provided for each entry
in the {Bodies} section of the data file:
atom-ID 3 M
N E F
ixx iyy izz ixy ixz iyz
x1 y1 z1
...
xN yN zN
0 1
1 2
2 3
...
0 1 2 -1
0 2 3 -1
...
1 2 3 4
diameter :pre
where M = 6 + 3*N + 2*E + 4*F + 1, and N is the number of vertices in
the body particle, E = number of edges, F = number of faces.
The integer line has three values: number of vertices (N), number of
edges (E) and number of faces (F). The floating point line(s) list 6
moments of inertia followed by the coordinates of the N vertices (x1
to zN) as 3N values, followed by 2N vertex indices corresponding to
the end points of the E edges, then 4*F vertex indices defining F
faces. The last value is the diameter value = the rounded diameter of
the sphere that surrounds each vertex. The diameter value can be
different for each body particle. These floating-point values can be
listed on as many lines as you wish; see the
"read_data"_read_data.html command for more details. Because the
maximum number of vertices per face is hard-coded to be 4
(i.e. quadrilaterals), faces with more than 4 vertices need to be
split into triangles or quadrilaterals. For triangular faces, the
last vertex index should be set to -1.
The ordering of the 4 vertices within a face should follow
the right-hand rule so that the normal vector of the face points
outwards from the center of mass.
The 6 moments of inertia (ixx,iyy,izz,ixy,ixz,iyz) should be the
values consistent with the current orientation of the rigid body
around its center of mass. The values are with respect to the
simulation box XYZ axes, not with respect to the principal axes of the
rigid body itself. LAMMPS performs the latter calculation internally.
The coordinates of each vertex are specified as its x,y,z displacement
from the center-of-mass of the body particle. The center-of-mass
position of the particle is specified by the x,y,z values in the
{Atoms} section of the data file.
For example, the following information would specify a cubic particle
whose edge length is 2.0 and rounded diameter is 0.5.
The orientation of the cube is aligned with the xyz coordinate axes
which is consistent with the 6 moments of inertia: ixx iyy izz ixy ixz
iyz = 0.667 0.667 0.667 0 0 0.
1 3 79
8 12 6
0.667 0.667 0.667 0 0 0
1 1 1
1 -1 1
-1 -1 1
-1 1 1
1 1 -1
1 -1 -1
-1 -1 -1
-1 1 -1
0 1
1 2
2 3
3 0
4 5
5 6
6 7
7 4
0 4
1 5
2 6
3 7
0 1 2 3
4 5 6 7
0 1 5 4
1 2 6 5
2 3 7 6
3 0 4 7
0.5 :pre
A rod in 3D, whose length is 4.0, mass 1.0 and rounded at two ends
by circles of diameter 0.5, is specified as follows:
1 1 13
2
0 1.33333 1.33333 0 0 0
-2 0 0
2 0 0
0.5 :pre
A sphere whose diameter is 3.0 and mass 1.0, is specified as follows:
1 1 10
1
0.9 0.9 0.9 0 0 0
0 0 0
3.0 :pre
The "pair_style
body/rounded/polhedron"_pair_body_rounded_polyhedron.html command can
be used with this body style to compute body/body interactions. The
"fix wall/body/polyhedron"_fix_wall_body_polygon.html command can be
used with this body style to compute the interaction of body particles
with a wall.
:line
For output purposes via the "compute
body/local"_compute_body_local.html and "dump local"_dump.html
commands, this body style produces one datum for each of the N
sub-particles in a body particle. The datum has 3 values:
1 = x position of vertex
2 = y position of vertex
3 = z position of vertex :pre
These values are the current position of the vertex within the
simulation domain, not a displacement from the center-of-mass (COM) of
the body particle itself. These values are calculated using the
current COM and orientation of the body particle.
For images created by the "dump image"_dump_image.html command, if the
{body} keyword is set, then each body particle is drawn as a polygon
consisting of N line segments. Note that the line segments are drawn
between the N vertices, which does not correspond exactly to the
physical extent of the body (because the "pair_style
rounded/polygon"_pair_body_rounded_polygon.html defines finite-size
spheres at those point and the line segments between the spheres are
tangent to the spheres). The drawn diameter of each line segment is
determined by the {bflag1} parameter for the {body} keyword. The
{bflag2} argument is ignored.
:line
:link(body-Fraige)
[(Fraige)] F. Y. Fraige, P. A. Langston, A. J. Matchett, J. Dodds,
Particuology, 6, 455 (2008).
:link(body-Wang)
[(Wang)] J. Wang, H. S. Yu, P. A. Langston, F. Y. Fraige, Granular
Matter, 13, 1 (2011).

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Use chunks to calculate system properties :h3
In LAMMS, "chunks" are collections of atoms, as defined by the
"compute chunk/atom"_compute_chunk_atom.html command, which assigns
each atom to a chunk ID (or to no chunk at all). The number of chunks
and the assignment of chunk IDs to atoms can be static or change over
time. Examples of "chunks" are molecules or spatial bins or atoms
with similar values (e.g. coordination number or potential energy).
The per-atom chunk IDs can be used as input to two other kinds of
commands, to calculate various properties of a system:
"fix ave/chunk"_fix_ave_chunk.html
any of the "compute */chunk"_compute.html commands :ul
Here a brief overview for each of the 4 kinds of chunk-related commands
is provided. Then some examples are given of how to compute different
properties with chunk commands.
Compute chunk/atom command: :h4
This compute can assign atoms to chunks of various styles. Only atoms
in the specified group and optional specified region are assigned to a
chunk. Here are some possible chunk definitions:
atoms in same molecule | chunk ID = molecule ID |
atoms of same atom type | chunk ID = atom type |
all atoms with same atom property (charge, radius, etc) | chunk ID = output of compute property/atom |
atoms in same cluster | chunk ID = output of "compute cluster/atom"_compute_cluster_atom.html command |
atoms in same spatial bin | chunk ID = bin ID |
atoms in same rigid body | chunk ID = molecule ID used to define rigid bodies |
atoms with similar potential energy | chunk ID = output of "compute pe/atom"_compute_pe_atom.html |
atoms with same local defect structure | chunk ID = output of "compute centro/atom"_compute_centro_atom.html or "compute coord/atom"_compute_coord_atom.html command :tb(s=|,c=2)
Note that chunk IDs are integer values, so for atom properties or
computes that produce a floating point value, they will be truncated
to an integer. You could also use the compute in a variable that
scales the floating point value to spread it across multiple integers.
Spatial bins can be of various kinds, e.g. 1d bins = slabs, 2d bins =
pencils, 3d bins = boxes, spherical bins, cylindrical bins.
This compute also calculates the number of chunks {Nchunk}, which is
used by other commands to tally per-chunk data. {Nchunk} can be a
static value or change over time (e.g. the number of clusters). The
chunk ID for an individual atom can also be static (e.g. a molecule
ID), or dynamic (e.g. what spatial bin an atom is in as it moves).
Note that this compute allows the per-atom output of other
"computes"_compute.html, "fixes"_fix.html, and
"variables"_variable.html to be used to define chunk IDs for each
atom. This means you can write your own compute or fix to output a
per-atom quantity to use as chunk ID. See the "Modify"_Modify.html
doc pages for info on how to do this. You can also define a "per-atom
variable"_variable.html in the input script that uses a formula to
generate a chunk ID for each atom.
Fix ave/chunk command: :h4
This fix takes the ID of a "compute
chunk/atom"_compute_chunk_atom.html command as input. For each chunk,
it then sums one or more specified per-atom values over the atoms in
each chunk. The per-atom values can be any atom property, such as
velocity, force, charge, potential energy, kinetic energy, stress,
etc. Additional keywords are defined for per-chunk properties like
density and temperature. More generally any per-atom value generated
by other "computes"_compute.html, "fixes"_fix.html, and "per-atom
variables"_variable.html, can be summed over atoms in each chunk.
Similar to other averaging fixes, this fix allows the summed per-chunk
values to be time-averaged in various ways, and output to a file. The
fix produces a global array as output with one row of values per
chunk.
Compute */chunk commands: :h4
The following computes operate on chunks of atoms to produce per-chunk
values. Any compute whose style name ends in "/chunk" is in this
category:
"compute com/chunk"_compute_com_chunk.html
"compute gyration/chunk"_compute_gyration_chunk.html
"compute inertia/chunk"_compute_inertia_chunk.html
"compute msd/chunk"_compute_msd_chunk.html
"compute property/chunk"_compute_property_chunk.html
"compute temp/chunk"_compute_temp_chunk.html
"compute torque/chunk"_compute_vcm_chunk.html
"compute vcm/chunk"_compute_vcm_chunk.html :ul
They each take the ID of a "compute
chunk/atom"_compute_chunk_atom.html command as input. As their names
indicate, they calculate the center-of-mass, radius of gyration,
moments of inertia, mean-squared displacement, temperature, torque,
and velocity of center-of-mass for each chunk of atoms. The "compute
property/chunk"_compute_property_chunk.html command can tally the
count of atoms in each chunk and extract other per-chunk properties.
The reason these various calculations are not part of the "fix
ave/chunk command"_fix_ave_chunk.html, is that each requires a more
complicated operation than simply summing and averaging over per-atom
values in each chunk. For example, many of them require calculation
of a center of mass, which requires summing mass*position over the
atoms and then dividing by summed mass.
All of these computes produce a global vector or global array as
output, wih one or more values per chunk. The output can be used in
various ways:
As input to the "fix ave/time"_fix_ave_time.html command, which can
write the values to a file and optionally time average them. :ulb,l
As input to the "fix ave/histo"_fix_ave_histo.html command to
histogram values across chunks. E.g. a histogram of cluster sizes or
molecule diffusion rates. :l
As input to special functions of "equal-style
variables"_variable.html, like sum() and max() and ave(). E.g. to
find the largest cluster or fastest diffusing molecule or average
radius-of-gyration of a set of molecules (chunks). :l,ule
Other chunk commands: :h4
"compute chunk/spread/atom"_compute_chunk_spread_atom.html
"compute reduce/chunk"_compute_reduce_chunk.html :ul
The "compute chunk/spread/atom"_compute_chunk_spread_atom.html command
spreads per-chunk values to each atom in the chunk, producing per-atom
values as its output. This can be useful for outputting per-chunk
values to a per-atom "dump file"_dump.html. Or for using an atom's
associated chunk value in an "atom-style variable"_variable.html. Or
as input to the "fix ave/chunk"_fix_ave_chunk.html command to
spatially average per-chunk values calculated by a per-chunk compute.
The "compute reduce/chunk"_compute_reduce_chunk.html command reduces a
peratom value across the atoms in each chunk to produce a value per
chunk. When used with the "compute
chunk/spread/atom"_compute_chunk_spread_atom.html command it can
create peratom values that induce a new set of chunks with a second
"compute chunk/atom"_compute_chunk_atom.html command.
Example calculations with chunks :h4
Here are examples using chunk commands to calculate various
properties:
(1) Average velocity in each of 1000 2d spatial bins:
compute cc1 all chunk/atom bin/2d x 0.0 0.1 y lower 0.01 units reduced
fix 1 all ave/chunk 100 10 1000 cc1 vx vy file tmp.out :pre
(2) Temperature in each spatial bin, after subtracting a flow
velocity:
compute cc1 all chunk/atom bin/2d x 0.0 0.1 y lower 0.1 units reduced
compute vbias all temp/profile 1 0 0 y 10
fix 1 all ave/chunk 100 10 1000 cc1 temp bias vbias file tmp.out :pre
(3) Center of mass of each molecule:
compute cc1 all chunk/atom molecule
compute myChunk all com/chunk cc1
fix 1 all ave/time 100 1 100 c_myChunk\[*\] file tmp.out mode vector :pre
(4) Total force on each molecule and ave/max across all molecules:
compute cc1 all chunk/atom molecule
fix 1 all ave/chunk 1000 1 1000 cc1 fx fy fz file tmp.out
variable xave equal ave(f_1\[2\])
variable xmax equal max(f_1\[2\])
thermo 1000
thermo_style custom step temp v_xave v_xmax :pre
(5) Histogram of cluster sizes:
compute cluster all cluster/atom 1.0
compute cc1 all chunk/atom c_cluster compress yes
compute size all property/chunk cc1 count
fix 1 all ave/histo 100 1 100 0 20 20 c_size mode vector ave running beyond ignore file tmp.histo :pre
(6) An example for using a per-chunk value to apply per-atom forces to
compress individual polymer chains (molecules) in a mixture, is
explained on the "compute
chunk/spread/atom"_compute_chunk_spread_atom.html command doc page.
(7) An example for using one set of per-chunk values for molecule
chunks, to create a 2nd set of micelle-scale chunks (clustered
molecules, due to hydrophobicity), is explained on the "compute
chunk/reduce"_compute_reduce_chunk.html command doc page.
(8) An example for using one set of per-chunk values (dipole moment
vectors) for molecule chunks, spreading the values to each atom in
each chunk, then defining a second set of chunks as spatial bins, and
using the "fix ave/chunk"_fix_ave_chunk.html command to calculate an
average dipole moment vector for each bin. This example is explained
on the "compute chunk/spread/atom"_compute_chunk_spread_atom.html
command doc page.

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Adiabatic core/shell model :h3
The adiabatic core-shell model by "Mitchell and
Fincham"_#MitchellFincham is a simple method for adding polarizability
to a system. In order to mimic the electron shell of an ion, a
satellite particle is attached to it. This way the ions are split into
a core and a shell where the latter is meant to react to the
electrostatic environment inducing polarizability. See the "Howto
polarizable"_Howto_polarizable.html doc page for a discussion of all
the polarizable models available in LAMMPS.
Technically, shells are attached to the cores by a spring force f =
k*r where k is a parameterized spring constant and r is the distance
between the core and the shell. The charges of the core and the shell
add up to the ion charge, thus q(ion) = q(core) + q(shell). This
setup introduces the ion polarizability (alpha) given by
alpha = q(shell)^2 / k. In a
similar fashion the mass of the ion is distributed on the core and the
shell with the core having the larger mass.
To run this model in LAMMPS, "atom_style"_atom_style.html {full} can
be used since atom charge and bonds are needed. Each kind of
core/shell pair requires two atom types and a bond type. The core and
shell of a core/shell pair should be bonded to each other with a
harmonic bond that provides the spring force. For example, a data file
for NaCl, as found in examples/coreshell, has this format:
432 atoms # core and shell atoms
216 bonds # number of core/shell springs :pre
4 atom types # 2 cores and 2 shells for Na and Cl
2 bond types :pre
0.0 24.09597 xlo xhi
0.0 24.09597 ylo yhi
0.0 24.09597 zlo zhi :pre
Masses # core/shell mass ratio = 0.1 :pre
1 20.690784 # Na core
2 31.90500 # Cl core
3 2.298976 # Na shell
4 3.54500 # Cl shell :pre
Atoms :pre
1 1 2 1.5005 0.00000000 0.00000000 0.00000000 # core of core/shell pair 1
2 1 4 -2.5005 0.00000000 0.00000000 0.00000000 # shell of core/shell pair 1
3 2 1 1.5056 4.01599500 4.01599500 4.01599500 # core of core/shell pair 2
4 2 3 -0.5056 4.01599500 4.01599500 4.01599500 # shell of core/shell pair 2
(...) :pre
Bonds # Bond topology for spring forces :pre
1 2 1 2 # spring for core/shell pair 1
2 2 3 4 # spring for core/shell pair 2
(...) :pre
Non-Coulombic (e.g. Lennard-Jones) pairwise interactions are only
defined between the shells. Coulombic interactions are defined
between all cores and shells. If desired, additional bonds can be
specified between cores.
The "special_bonds"_special_bonds.html command should be used to
turn-off the Coulombic interaction within core/shell pairs, since that
interaction is set by the bond spring. This is done using the
"special_bonds"_special_bonds.html command with a 1-2 weight = 0.0,
which is the default value. It needs to be considered whether one has
to adjust the "special_bonds"_special_bonds.html weighting according
to the molecular topology since the interactions of the shells are
bypassed over an extra bond.
Note that this core/shell implementation does not require all ions to
be polarized. One can mix core/shell pairs and ions without a
satellite particle if desired.
Since the core/shell model permits distances of r = 0.0 between the
core and shell, a pair style with a "cs" suffix needs to be used to
implement a valid long-range Coulombic correction. Several such pair
styles are provided in the CORESHELL package. See "this doc
page"_pair_cs.html for details. All of the core/shell enabled pair
styles require the use of a long-range Coulombic solver, as specified
by the "kspace_style"_kspace_style.html command. Either the PPPM or
Ewald solvers can be used.
For the NaCL example problem, these pair style and bond style settings
are used:
pair_style born/coul/long/cs 20.0 20.0
pair_coeff * * 0.0 1.000 0.00 0.00 0.00
pair_coeff 3 3 487.0 0.23768 0.00 1.05 0.50 #Na-Na
pair_coeff 3 4 145134.0 0.23768 0.00 6.99 8.70 #Na-Cl
pair_coeff 4 4 405774.0 0.23768 0.00 72.40 145.40 #Cl-Cl :pre
bond_style harmonic
bond_coeff 1 63.014 0.0
bond_coeff 2 25.724 0.0 :pre
When running dynamics with the adiabatic core/shell model, the
following issues should be considered. The relative motion of
the core and shell particles corresponds to the polarization,
hereby an instantaneous relaxation of the shells is approximated
and a fast core/shell spring frequency ensures a nearly constant
internal kinetic energy during the simulation.
Thermostats can alter this polarization behavior, by scaling the
internal kinetic energy, meaning the shell will not react freely to
its electrostatic environment.
Therefore it is typically desirable to decouple the relative motion of
the core/shell pair, which is an imaginary degree of freedom, from the
real physical system. To do that, the "compute
temp/cs"_compute_temp_cs.html command can be used, in conjunction with
any of the thermostat fixes, such as "fix nvt"_fix_nh.html or "fix
langevin"_fix_langevin.html. This compute uses the center-of-mass velocity
of the core/shell pairs to calculate a temperature, and insures that
velocity is what is rescaled for thermostatting purposes. This
compute also works for a system with both core/shell pairs and
non-polarized ions (ions without an attached satellite particle). The
"compute temp/cs"_compute_temp_cs.html command requires input of two
groups, one for the core atoms, another for the shell atoms.
Non-polarized ions which might also be included in the treated system
should not be included into either of these groups, they are taken
into account by the {group-ID} (2nd argument) of the compute. The
groups can be defined using the "group {type}"_group.html command.
Note that to perform thermostatting using this definition of
temperature, the "fix modify temp"_fix_modify.html command should be
used to assign the compute to the thermostat fix. Likewise the
"thermo_modify temp"_thermo_modify.html command can be used to make
this temperature be output for the overall system.
For the NaCl example, this can be done as follows:
group cores type 1 2
group shells type 3 4
compute CSequ all temp/cs cores shells
fix thermoberendsen all temp/berendsen 1427 1427 0.4 # thermostat for the true physical system
fix thermostatequ all nve # integrator as needed for the berendsen thermostat
fix_modify thermoberendsen temp CSequ
thermo_modify temp CSequ # output of center-of-mass derived temperature :pre
The pressure for the core/shell system is computed via the regular
LAMMPS convention by "treating the cores and shells as individual
particles"_#MitchellFincham2. For the thermo output of the pressure
as well as for the application of a barostat, it is necessary to
use an additional "pressure"_compute_pressure.html compute based on
the default "temperature"_compute_temp.html and specifying it as a
second argument in "fix modify"_fix_modify.html and
"thermo_modify"_thermo_modify.html resulting in:
(...)
compute CSequ all temp/cs cores shells
compute thermo_press_lmp all pressure thermo_temp # pressure for individual particles
thermo_modify temp CSequ press thermo_press_lmp # modify thermo to regular pressure
fix press_bar all npt temp 300 300 0.04 iso 0 0 0.4
fix_modify press_bar temp CSequ press thermo_press_lmp # pressure modification for correct kinetic scalar :pre
If "compute temp/cs"_compute_temp_cs.html is used, the decoupled
relative motion of the core and the shell should in theory be
stable. However numerical fluctuation can introduce a small
momentum to the system, which is noticeable over long trajectories.
Therefore it is recommendable to use the "fix
momentum"_fix_momentum.html command in combination with "compute
temp/cs"_compute_temp_cs.html when equilibrating the system to
prevent any drift.
When initializing the velocities of a system with core/shell pairs, it
is also desirable to not introduce energy into the relative motion of
the core/shell particles, but only assign a center-of-mass velocity to
the pairs. This can be done by using the {bias} keyword of the
"velocity create"_velocity.html command and assigning the "compute
temp/cs"_compute_temp_cs.html command to the {temp} keyword of the
"velocity"_velocity.html command, e.g.
velocity all create 1427 134 bias yes temp CSequ
velocity all scale 1427 temp CSequ :pre
To maintain the correct polarizability of the core/shell pairs, the
kinetic energy of the internal motion shall remain nearly constant.
Therefore the choice of spring force and mass ratio need to ensure
much faster relative motion of the 2 atoms within the core/shell pair
than their center-of-mass velocity. This allows the shells to
effectively react instantaneously to the electrostatic environment and
limits energy transfer to or from the core/shell oscillators.
This fast movement also dictates the timestep that can be used.
The primary literature of the adiabatic core/shell model suggests that
the fast relative motion of the core/shell pairs only allows negligible
energy transfer to the environment.
The mentioned energy transfer will typically lead to a small drift
in total energy over time. This internal energy can be monitored
using the "compute chunk/atom"_compute_chunk_atom.html and "compute
temp/chunk"_compute_temp_chunk.html commands. The internal kinetic
energies of each core/shell pair can then be summed using the sum()
special function of the "variable"_variable.html command. Or they can
be time/averaged and output using the "fix ave/time"_fix_ave_time.html
command. To use these commands, each core/shell pair must be defined
as a "chunk". If each core/shell pair is defined as its own molecule,
the molecule ID can be used to define the chunks. If cores are bonded
to each other to form larger molecules, the chunks can be identified
by the "fix property/atom"_fix_property_atom.html via assigning a
core/shell ID to each atom using a special field in the data file read
by the "read_data"_read_data.html command. This field can then be
accessed by the "compute property/atom"_compute_property_atom.html
command, to use as input to the "compute
chunk/atom"_compute_chunk_atom.html command to define the core/shell
pairs as chunks.
For example if core/shell pairs are the only molecules:
read_data NaCl_CS_x0.1_prop.data
compute prop all property/atom molecule
compute cs_chunk all chunk/atom c_prop
compute cstherm all temp/chunk cs_chunk temp internal com yes cdof 3.0 # note the chosen degrees of freedom for the core/shell pairs
fix ave_chunk all ave/time 10 1 10 c_cstherm file chunk.dump mode vector :pre
For example if core/shell pairs and other molecules are present:
fix csinfo all property/atom i_CSID # property/atom command
read_data NaCl_CS_x0.1_prop.data fix csinfo NULL CS-Info # atom property added in the data-file
compute prop all property/atom i_CSID
(...) :pre
The additional section in the date file would be formatted like this:
CS-Info # header of additional section :pre
1 1 # column 1 = atom ID, column 2 = core/shell ID
2 1
3 2
4 2
5 3
6 3
7 4
8 4
(...) :pre
:line
:link(MitchellFincham)
[(Mitchell and Fincham)] Mitchell, Fincham, J Phys Condensed Matter,
5, 1031-1038 (1993).
:link(MitchellFincham2)
[(Fincham)] Fincham, Mackrodt and Mitchell, J Phys Condensed Matter,
6, 393-404 (1994).

116
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@ -1,116 +0,0 @@
"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Coupling LAMMPS to other codes :h3
LAMMPS is designed to allow it to be coupled to other codes. For
example, a quantum mechanics code might compute forces on a subset of
atoms and pass those forces to LAMMPS. Or a continuum finite element
(FE) simulation might use atom positions as boundary conditions on FE
nodal points, compute a FE solution, and return interpolated forces on
MD atoms.
LAMMPS can be coupled to other codes in at least 4 ways. Each has
advantages and disadvantages, which you'll have to think about in the
context of your application.
:line
(1) Define a new "fix"_fix.html command that calls the other code. In
this scenario, LAMMPS is the driver code. During its timestepping,
the fix is invoked, and can make library calls to the other code,
which has been linked to LAMMPS as a library. This is the way the
"POEMS"_poems package that performs constrained rigid-body motion on
groups of atoms is hooked to LAMMPS. See the "fix
poems"_fix_poems.html command for more details. See the
"Modify"_Modify.html doc pages for info on how to add a new fix to
LAMMPS.
:link(poems,http://www.rpi.edu/~anderk5/lab)
:line
(2) Define a new LAMMPS command that calls the other code. This is
conceptually similar to method (1), but in this case LAMMPS and the
other code are on a more equal footing. Note that now the other code
is not called during the timestepping of a LAMMPS run, but between
runs. The LAMMPS input script can be used to alternate LAMMPS runs
with calls to the other code, invoked via the new command. The
"run"_run.html command facilitates this with its {every} option, which
makes it easy to run a few steps, invoke the command, run a few steps,
invoke the command, etc.
In this scenario, the other code can be called as a library, as in
(1), or it could be a stand-alone code, invoked by a system() call
made by the command (assuming your parallel machine allows one or more
processors to start up another program). In the latter case the
stand-alone code could communicate with LAMMPS through files that the
command writes and reads.
See the "Modify command"_Modify_command.html doc page for info on how
to add a new command to LAMMPS.
:line
(3) Use LAMMPS as a library called by another code. In this case the
other code is the driver and calls LAMMPS as needed. Or a wrapper
code could link and call both LAMMPS and another code as libraries.
Again, the "run"_run.html command has options that allow it to be
invoked with minimal overhead (no setup or clean-up) if you wish to do
multiple short runs, driven by another program.
Examples of driver codes that call LAMMPS as a library are included in
the examples/COUPLE directory of the LAMMPS distribution; see
examples/COUPLE/README for more details:
simple: simple driver programs in C++ and C which invoke LAMMPS as a
library :ulb,l
lammps_quest: coupling of LAMMPS and "Quest"_quest, to run classical
MD with quantum forces calculated by a density functional code :l
lammps_spparks: coupling of LAMMPS and "SPPARKS"_spparks, to couple
a kinetic Monte Carlo model for grain growth using MD to calculate
strain induced across grain boundaries :l
:ule
:link(quest,http://dft.sandia.gov/Quest)
:link(spparks,http://www.sandia.gov/~sjplimp/spparks.html)
The "Build basics"_Build_basics.html doc page describes how to build
LAMMPS as a library. Once this is done, you can interface with LAMMPS
either via C++, C, Fortran, or Python (or any other language that
supports a vanilla C-like interface). For example, from C++ you could
create one (or more) "instances" of LAMMPS, pass it an input script to
process, or execute individual commands, all by invoking the correct
class methods in LAMMPS. From C or Fortran you can make function
calls to do the same things. See the "Python"_Python_head.html doc
pages for a description of the Python wrapper provided with LAMMPS
that operates through the LAMMPS library interface.
The files src/library.cpp and library.h contain the C-style interface
to LAMMPS. See the "Howto library"_Howto_library.html doc page for a
description of the interface and how to extend it for your needs.
Note that the lammps_open() function that creates an instance of
LAMMPS takes an MPI communicator as an argument. This means that
instance of LAMMPS will run on the set of processors in the
communicator. Thus the calling code can run LAMMPS on all or a subset
of processors. For example, a wrapper script might decide to
alternate between LAMMPS and another code, allowing them both to run
on all the processors. Or it might allocate half the processors to
LAMMPS and half to the other code and run both codes simultaneously
before syncing them up periodically. Or it might instantiate multiple
instances of LAMMPS to perform different calculations.
:line
(4) Couple LAMMPS with another code in a client/server mode. This is
described on the "Howto client/server"_Howto_client_server.html doc
page.

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Calculate diffusion coefficients :h3
The diffusion coefficient D of a material can be measured in at least
2 ways using various options in LAMMPS. See the examples/DIFFUSE
directory for scripts that implement the 2 methods discussed here for
a simple Lennard-Jones fluid model.
The first method is to measure the mean-squared displacement (MSD) of
the system, via the "compute msd"_compute_msd.html command. The slope
of the MSD versus time is proportional to the diffusion coefficient.
The instantaneous MSD values can be accumulated in a vector via the
"fix vector"_fix_vector.html command, and a line fit to the vector to
compute its slope via the "variable slope"_variable.html function, and
thus extract D.
The second method is to measure the velocity auto-correlation function
(VACF) of the system, via the "compute vacf"_compute_vacf.html
command. The time-integral of the VACF is proportional to the
diffusion coefficient. The instantaneous VACF values can be
accumulated in a vector via the "fix vector"_fix_vector.html command,
and time integrated via the "variable trap"_variable.html function,
and thus extract D.
:line

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Long-range dispersion settings :h3
The PPPM method computes interactions by splitting the pair potential
into two parts, one of which is computed in a normal pairwise fashion,
the so-called real-space part, and one of which is computed using the
Fourier transform, the so called reciprocal-space or kspace part. For
both parts, the potential is not computed exactly but is approximated.
Thus, there is an error in both parts of the computation, the
real-space and the kspace error. The just mentioned facts are true
both for the PPPM for Coulomb as well as dispersion interactions. The
deciding difference - and also the reason why the parameters for
pppm/disp have to be selected with more care - is the impact of the
errors on the results: The kspace error of the PPPM for Coulomb and
dispersion interaction and the real-space error of the PPPM for
Coulomb interaction have the character of noise. In contrast, the
real-space error of the PPPM for dispersion has a clear physical
interpretation: the underprediction of cohesion. As a consequence, the
real-space error has a much stronger effect than the kspace error on
simulation results for pppm/disp. Parameters must thus be chosen in a
way that this error is much smaller than the kspace error.
When using pppm/disp and not making any specifications on the PPPM
parameters via the kspace modify command, parameters will be tuned
such that the real-space error and the kspace error are equal. This
will result in simulations that are either inaccurate or slow, both of
which is not desirable. For selecting parameters for the pppm/disp
that provide fast and accurate simulations, there are two approaches,
which both have their up- and downsides.
The first approach is to set desired real-space an kspace accuracies
via the {kspace_modify force/disp/real} and {kspace_modify
force/disp/kspace} commands. Note that the accuracies have to be
specified in force units and are thus dependent on the chosen unit
settings. For real units, 0.0001 and 0.002 seem to provide reasonable
accurate and efficient computations for the real-space and kspace
accuracies. 0.002 and 0.05 work well for most systems using lj
units. PPPM parameters will be generated based on the desired
accuracies. The upside of this approach is that it usually provides a
good set of parameters and will work for both the {kspace_modify diff
ad} and {kspace_modify diff ik} options. The downside of the method
is that setting the PPPM parameters will take some time during the
initialization of the simulation.
The second approach is to set the parameters for the pppm/disp
explicitly using the {kspace_modify mesh/disp}, {kspace_modify
order/disp}, and {kspace_modify gewald/disp} commands. This approach
requires a more experienced user who understands well the impact of
the choice of parameters on the simulation accuracy and
performance. This approach provides a fast initialization of the
simulation. However, it is sensitive to errors: A combination of
parameters that will perform well for one system might result in
far-from-optimal conditions for other simulations. For example,
parameters that provide accurate and fast computations for
all-atomistic force fields can provide insufficient accuracy or
united-atomistic force fields (which is related to that the latter
typically have larger dispersion coefficients).
To avoid inaccurate or inefficient simulations, the pppm/disp stops
simulations with an error message if no action is taken to control the
PPPM parameters. If the automatic parameter generation is desired and
real-space and kspace accuracies are desired to be equal, this error
message can be suppressed using the {kspace_modify disp/auto yes}
command.
A reasonable approach that combines the upsides of both methods is to
make the first run using the {kspace_modify force/disp/real} and
{kspace_modify force/disp/kspace} commands, write down the PPPM
parameters from the output, and specify these parameters using the
second approach in subsequent runs (which have the same composition,
force field, and approximately the same volume).
Concerning the performance of the pppm/disp there are two more things
to consider. The first is that when using the pppm/disp, the cutoff
parameter does no longer affect the accuracy of the simulation
(subject to that gewald/disp is adjusted when changing the cutoff).
The performance can thus be increased by examining different values
for the cutoff parameter. A lower bound for the cutoff is only set by
the truncation error of the repulsive term of pair potentials.
The second is that the mixing rule of the pair style has an impact on
the computation time when using the pppm/disp. Fastest computations
are achieved when using the geometric mixing rule. Using the
arithmetic mixing rule substantially increases the computational cost.
The computational overhead can be reduced using the {kspace_modify
mix/disp geom} and {kspace_modify splittol} commands. The first
command simply enforces geometric mixing of the dispersion
coefficients in kspace computations. This introduces some error in
the computations but will also significantly speed-up the
simulations. The second keyword sets the accuracy with which the
dispersion coefficients are approximated using a matrix factorization
approach. This may result in better accuracy then using the first
command, but will usually also not provide an equally good increase of
efficiency.
Finally, pppm/disp can also be used when no mixing rules apply.
This can be achieved using the {kspace_modify mix/disp none} command.
Note that the code does not check automatically whether any mixing
rule is fulfilled. If mixing rules do not apply, the user will have
to specify this command explicitly.

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Drude induced dipoles :h3
The thermalized Drude model represents induced dipoles by a pair of
charges (the core atom and the Drude particle) connected by a harmonic
spring. See the "Howto polarizable"_Howto_polarizable.html doc page
for a discussion of all the polarizable models available in LAMMPS.
The Drude model has a number of features aimed at its use in
molecular systems ("Lamoureux and Roux"_#howto-Lamoureux):
Thermostatting of the additional degrees of freedom associated with the
induced dipoles at very low temperature, in terms of the reduced
coordinates of the Drude particles with respect to their cores. This
makes the trajectory close to that of relaxed induced dipoles. :ulb,l
Consistent definition of 1-2 to 1-4 neighbors. A core-Drude particle
pair represents a single (polarizable) atom, so the special screening
factors in a covalent structure should be the same for the core and
the Drude particle. Drude particles have to inherit the 1-2, 1-3, 1-4
special neighbor relations from their respective cores. :l
Stabilization of the interactions between induced dipoles. Drude
dipoles on covalently bonded atoms interact too strongly due to the
short distances, so an atom may capture the Drude particle of a
neighbor, or the induced dipoles within the same molecule may align
too much. To avoid this, damping at short range can be done by Thole
functions (for which there are physical grounds). This Thole damping
is applied to the point charges composing the induced dipole (the
charge of the Drude particle and the opposite charge on the core, not
to the total charge of the core atom). :l,ule
A detailed tutorial covering the usage of Drude induced dipoles in
LAMMPS is on the "Howto drude2e"_Howto_drude2.html doc page.
As with the core-shell model, the cores and Drude particles should
appear in the data file as standard atoms. The same holds for the
springs between them, which are described by standard harmonic bonds.
The nature of the atoms (core, Drude particle or non-polarizable) is
specified via the "fix drude"_fix_drude.html command. The special
list of neighbors is automatically refactored to account for the
equivalence of core and Drude particles as regards special 1-2 to 1-4
screening. It may be necessary to use the {extra/special/per/atom}
keyword of the "read_data"_read_data.html command. If using "fix
shake"_fix_shake.html, make sure no Drude particle is in this fix
group.
There are two ways to thermostat the Drude particles at a low
temperature: use either "fix langevin/drude"_fix_langevin_drude.html
for a Langevin thermostat, or "fix
drude/transform/*"_fix_drude_transform.html for a Nose-Hoover
thermostat. The former requires use of the command "comm_modify vel
yes"_comm_modify.html. The latter requires two separate integration
fixes like {nvt} or {npt}. The correct temperatures of the reduced
degrees of freedom can be calculated using the "compute
temp/drude"_compute_temp_drude.html. This requires also to use the
command {comm_modify vel yes}.
Short-range damping of the induced dipole interactions can be achieved
using Thole functions through the "pair style
thole"_pair_thole.html in "pair_style hybrid/overlay"_pair_hybrid.html
with a Coulomb pair style. It may be useful to use {coul/long/cs} or
similar from the CORESHELL package if the core and Drude particle come
too close, which can cause numerical issues.
:line
:link(howto-Lamoureux)
[(Lamoureux and Roux)] G. Lamoureux, B. Roux, J. Chem. Phys 119, 3025 (2003)

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"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Tutorial for Thermalized Drude oscillators in LAMMPS :h3
This tutorial explains how to use Drude oscillators in LAMMPS to
simulate polarizable systems using the USER-DRUDE package. As an
illustration, the input files for a simulation of 250 phenol molecules
are documented. First of all, LAMMPS has to be compiled with the
USER-DRUDE package activated. Then, the data file and input scripts
have to be modified to include the Drude dipoles and how to handle
them.
:line
[Overview of Drude induced dipoles]
Polarizable atoms acquire an induced electric dipole moment under the
action of an external electric field, for example the electric field
created by the surrounding particles. Drude oscillators represent
these dipoles by two fixed charges: the core (DC) and the Drude
particle (DP) bound by a harmonic potential. The Drude particle can be
thought of as the electron cloud whose center can be displaced from
the position of the corresponding nucleus.
The sum of the masses of a core-Drude pair should be the mass of the
initial (unsplit) atom, \(m_C + m_D = m\). The sum of their charges
should be the charge of the initial (unsplit) atom, \(q_C + q_D = q\).
A harmonic potential between the core and Drude partners should be
present, with force constant \(k_D\) and an equilibrium distance of
zero. The (half-)stiffness of the "harmonic bond"_bond_harmonic.html
\(K_D = k_D/2\) and the Drude charge \(q_D\) are related to the atom
polarizability \(\alpha\) by
\begin\{equation\} K_D = \frac 1 2\, \frac \{q_D^2\} \alpha
\end\{equation\}
Ideally, the mass of the Drude particle should be small, and the
stiffness of the harmonic bond should be large, so that the Drude
particle remains close ot the core. The values of Drude mass, Drude
charge, and force constant can be chosen following different
strategies, as in the following examples of polarizable force
fields:
"Lamoureux and Roux"_#Lamoureux2 suggest adopting a global half-stiffness, \
\(K_D\) = 500 kcal/(mol Ang \(\{\}^2\)) - which corresponds to a force \
constant \(k_D\) = 4184 kJ/(mol Ang \(\{\}^2\)) - for all types of \
core-Drude bond, a global mass \(m_D\) = 0.4 g/mol (or u) for all types \
of Drude particles, and to calculate the Drude charges for individual \
atom types from the atom polarizabilities using equation (1). This \
choice is followed in the polarizable CHARMM force field. :ulb,l
Alternately "Schroeder and Steinhauser"_#Schroeder suggest adopting a global \
charge \(q_D\) = -1.0e and a global mass \(m_D\) = 0.1 g/mol (or u) \
for all Drude particles, and to calculate the force constant for each \
type of core-Drude bond from equation (1). The timesteps used by these \
authors are between 0.5 and 2 fs, with the degrees of freedom of the \
Drude oscillators kept cold at 1 K. :l
In both these force fields hydrogen atoms are treated as non-polarizable. :l
:ule
The motion of of the Drude particles can be calculated by minimizing
the energy of the induced dipoles at each timestep, by an iterative,
self-consistent procedure. The Drude particles can be massless and
therefore do not contribute to the kinetic energy. However, the
relaxed method is computational slow. An extended-lagrangian method
can be used to calculate the positions of the Drude particles, but
this requires them to have mass. It is important in this case to
decouple the degrees of freedom associated with the Drude oscillators
from those of the normal atoms. Thermalizing the Drude dipoles at
temperatures comparable to the rest of the simulation leads to several
problems (kinetic energy transfer, very short timestep, etc.), which
can be remedied by the "cold Drude" technique ("Lamoureux and
Roux"_#Lamoureux2).
Two closely related models are used to represent polarization through
"charges on a spring": the core-shell model and the Drude
model. Although the basic idea is the same, the core-shell model is
normally used for ionic/crystalline materials, whereas the Drude model
is normally used for molecular systems and fluid states. In ionic
crystals the symmetry around each ion and the distance between them
are such that the core-shell model is sufficiently stable. But to be
applicable to molecular/covalent systems the Drude model includes two
important features:
The possibility to thermostat the additional degrees of freedom \
associated with the induced dipoles at very low temperature, in terms \
of the reduced coordinates of the Drude particles with respect to \
their cores. This makes the trajectory close to that of relaxed \
induced dipoles. :olb,l
The Drude dipoles on covalently bonded atoms interact too strongly \
due to the short distances, so an atom may capture the Drude particle \
(shell) of a neighbor, or the induced dipoles within the same molecule \
may align too much. To avoid this, damping at short of the \
interactions between the point charges composing the induced dipole \
can be done by "Thole"_#Thole2 functions. :l
:ole
:line
[Preparation of the data file]
The data file is similar to a standard LAMMPS data file for
{atom_style full}. The DPs and the {harmonic bonds} connecting them
to their DC should appear in the data file as normal atoms and bonds.
You can use the {polarizer} tool (Python script distributed with the
USER-DRUDE package) to convert a non-polarizable data file (here
{data.102494.lmp}) to a polarizable data file ({data-p.lmp})
polarizer -q -f phenol.dff data.102494.lmp data-p.lmp :pre
This will automatically insert the new atoms and bonds.
The masses and charges of DCs and DPs are computed
from {phenol.dff}, as well as the DC-DP bond constants. The file
{phenol.dff} contains the polarizabilities of the atom types
and the mass of the Drude particles, for instance:
# units: kJ/mol, A, deg
# kforce is in the form k/2 r_D^2
# type m_D/u q_D/e k_D alpha/A3 thole
OH 0.4 -1.0 4184.0 0.63 0.67
CA 0.4 -1.0 4184.0 1.36 2.51
CAI 0.4 -1.0 4184.0 1.09 2.51 :pre
The hydrogen atoms are absent from this file, so they will be treated
as non-polarizable atoms. In the non-polarizable data file
{data.102494.lmp}, atom names corresponding to the atom type numbers
have to be specified as comments at the end of lines of the {Masses}
section. You probably need to edit it to add these names. It should
look like
Masses :pre
1 12.011 # CAI
2 12.011 # CA
3 15.999 # OH
4 1.008 # HA
5 1.008 # HO :pre
:line
[Basic input file]
The atom style should be set to (or derive from) {full}, so that you
can define atomic charges and molecular bonds, angles, dihedrals...
The {polarizer} tool also outputs certain lines related to the input
script (the use of these lines will be explained below). In order for
LAMMPS to recognize that you are using Drude oscillators, you should
use the fix {drude}. The command is
fix DRUDE all drude C C C N N D D D :pre
The N, C, D following the {drude} keyword have the following meaning:
There is one tag for each atom type. This tag is C for DCs, D for DPs
and N for non-polarizable atoms. Here the atom types 1 to 3 (C and O
atoms) are DC, atom types 4 and 5 (H atoms) are non-polarizable and
the atom types 6 to 8 are the newly created DPs.
By recognizing the fix {drude}, LAMMPS will find and store matching
DC-DP pairs and will treat DP as equivalent to their DC in the
{special bonds} relations. It may be necessary to extend the space
for storing such special relations. In this case extra space should
be reserved by using the {extra/special/per/atom} keyword of either
the "read_data"_read_data.html or "create_box"_create_box.html
command. With our phenol, there is 1 more special neighbor for which
space is required. Otherwise LAMMPS crashes and gives the required
value.
read_data data-p.lmp extra/special/per/atom 1 :pre
Let us assume we want to run a simple NVT simulation at 300 K. Note
that Drude oscillators need to be thermalized at a low temperature in
order to approximate a self-consistent field (SCF), therefore it is not
possible to simulate an NVE ensemble with this package. Since dipoles
are approximated by a charged DC-DP pair, the {pair_style} must
include Coulomb interactions, for instance {lj/cut/coul/long} with
{kspace_style pppm}. For example, with a cutoff of 10. and a precision
1.e-4:
pair_style lj/cut/coul/long 10.0
kspace_style pppm 1.0e-4 :pre
As compared to the non-polarizable input file, {pair_coeff} lines need
to be added for the DPs. Since the DPs have no Lennard-Jones
interactions, their {epsilon} is 0. so the only {pair_coeff} line
that needs to be added is
pair_coeff * 6* 0.0 0.0 # All-DPs :pre
Now for the thermalization, the simplest choice is to use the "fix
langevin/drude"_fix_langevin_drude.html.
fix LANG all langevin/drude 300. 100 12435 1. 20 13977 :pre
This applies a Langevin thermostat at temperature 300. to the centers
of mass of the DC-DP pairs, with relaxation time 100 and with random
seed 12345. This fix applies also a Langevin thermostat at temperature
1. to the relative motion of the DPs around their DCs, with relaxation
time 20 and random seed 13977. Only the DCs and non-polarizable
atoms need to be in this fix's group. LAMMPS will thermostat the DPs
together with their DC. For this, ghost atoms need to know their
velocities. Thus you need to add the following command:
comm_modify vel yes :pre
In order to avoid that the center of mass of the whole system
drifts due to the random forces of the Langevin thermostat on DCs, you
can add the {zero yes} option at the end of the fix line.
If the fix {shake} is used to constrain the C-H bonds, it should be
invoked after the fix {langevin/drude} for more accuracy.
fix SHAKE ATOMS shake 0.0001 20 0 t 4 5 :pre
NOTE: The group of the fix {shake} must not include the DPs. If the
group {ATOMS} is defined by non-DPs atom types, you could use
Since the fix {langevin/drude} does not perform time integration (just
modification of forces but no position/velocity updates), the fix
{nve} should be used in conjunction.
fix NVE all nve :pre
Finally, do not forget to update the atom type elements if you use
them in a {dump_modify ... element ...} command, by adding the element
type of the DPs. Here for instance
dump DUMP all custom 10 dump.lammpstrj id mol type element x y z ix iy iz
dump_modify DUMP element C C O H H D D D :pre
The input file should now be ready for use!
You will notice that the global temperature {thermo_temp} computed by
LAMMPS is not 300. K as wanted. This is because LAMMPS treats DPs as
standard atoms in his default compute. If you want to output the
temperatures of the DC-DP pair centers of mass and of the DPs relative
to their DCs, you should use the "compute
temp_drude"_compute_temp_drude.html
compute TDRUDE all temp/drude :pre
And then output the correct temperatures of the Drude oscillators
using {thermo_style custom} with respectively {c_TDRUDE\[1\]} and
{c_TDRUDE\[2\]}. These should be close to 300.0 and 1.0 on average.
thermo_style custom step temp c_TDRUDE\[1\] c_TDRUDE\[2\] :pre
:line
[Thole screening]
Dipolar interactions represented by point charges on springs may not
be stable, for example if the atomic polarizability is too high for
instance, a DP can escape from its DC and be captured by another DC,
which makes the force and energy diverge and the simulation
crash. Even without reaching this extreme case, the correlation
between nearby dipoles on the same molecule may be exaggerated. Often,
special bond relations prevent bonded neighboring atoms to see the
charge of each other's DP, so that the problem does not always appear.
It is possible to use screened dipole-dipole interactions by using the
"{pair_style thole}"_pair_thole.html. This is implemented as a
correction to the Coulomb pair_styles, which dampens at short distance
the interactions between the charges representing the induced dipoles.
It is to be used as {hybrid/overlay} with any standard {coul} pair
style. In our example, we would use
pair_style hybrid/overlay lj/cut/coul/long 10.0 thole 2.6 10.0 :pre
This tells LAMMPS that we are using two pair_styles. The first one is
as above ({lj/cut/coul/long 10.0}). The second one is a {thole}
pair_style with default screening factor 2.6 ("Noskov"_#Noskov2) and
cutoff 10.0.
Since {hybrid/overlay} does not support mixing rules, the interaction
coefficients of all the pairs of atom types with i < j should be
explicitly defined. The output of the {polarizer} script can be used
to complete the {pair_coeff} section of the input file. In our
example, this will look like:
pair_coeff 1 1 lj/cut/coul/long 0.0700 3.550
pair_coeff 1 2 lj/cut/coul/long 0.0700 3.550
pair_coeff 1 3 lj/cut/coul/long 0.1091 3.310
pair_coeff 1 4 lj/cut/coul/long 0.0458 2.985
pair_coeff 2 2 lj/cut/coul/long 0.0700 3.550
pair_coeff 2 3 lj/cut/coul/long 0.1091 3.310
pair_coeff 2 4 lj/cut/coul/long 0.0458 2.985
pair_coeff 3 3 lj/cut/coul/long 0.1700 3.070
pair_coeff 3 4 lj/cut/coul/long 0.0714 2.745
pair_coeff 4 4 lj/cut/coul/long 0.0300 2.420
pair_coeff * 5 lj/cut/coul/long 0.0000 0.000
pair_coeff * 6* lj/cut/coul/long 0.0000 0.000
pair_coeff 1 1 thole 1.090 2.510
pair_coeff 1 2 thole 1.218 2.510
pair_coeff 1 3 thole 0.829 1.590
pair_coeff 1 6 thole 1.090 2.510
pair_coeff 1 7 thole 1.218 2.510
pair_coeff 1 8 thole 0.829 1.590
pair_coeff 2 2 thole 1.360 2.510
pair_coeff 2 3 thole 0.926 1.590
pair_coeff 2 6 thole 1.218 2.510
pair_coeff 2 7 thole 1.360 2.510
pair_coeff 2 8 thole 0.926 1.590
pair_coeff 3 3 thole 0.630 0.670
pair_coeff 3 6 thole 0.829 1.590
pair_coeff 3 7 thole 0.926 1.590
pair_coeff 3 8 thole 0.630 0.670
pair_coeff 6 6 thole 1.090 2.510
pair_coeff 6 7 thole 1.218 2.510
pair_coeff 6 8 thole 0.829 1.590
pair_coeff 7 7 thole 1.360 2.510
pair_coeff 7 8 thole 0.926 1.590
pair_coeff 8 8 thole 0.630 0.670 :pre
For the {thole} pair style the coefficients are
the atom polarizability in units of cubic length :olb,l
the screening factor of the Thole function (optional, default value
specified by the pair_style command) :l
the cutoff (optional, default value defined by the pair_style command) :l
:ole
The special neighbors have charge-charge and charge-dipole
interactions screened by the {coul} factors of the {special_bonds}
command (0.0, 0.0, and 0.5 in the example above). Without using the
pair_style {thole}, dipole-dipole interactions are screened by the
same factor. By using the pair_style {thole}, dipole-dipole
interactions are screened by Thole's function, whatever their special
relationship (except within each DC-DP pair of course). Consider for
example 1-2 neighbors: using the pair_style {thole}, their dipoles
will see each other (despite the {coul} factor being 0.) and the
interactions between these dipoles will be damped by Thole's function.
:line
[Thermostats and barostats]
Using a Nose-Hoover barostat with the {langevin/drude} thermostat is
straightforward using fix {nph} instead of {nve}. For example:
fix NPH all nph iso 1. 1. 500 :pre
It is also possible to use a Nose-Hoover instead of a Langevin
thermostat. This requires to use "{fix
drude/transform}"_fix_drude_transform.html just before and after the
time integration fixes. The {fix drude/transform/direct} converts the
atomic masses, positions, velocities and forces into a reduced
representation, where the DCs transform into the centers of mass of
the DC-DP pairs and the DPs transform into their relative position
with respect to their DC. The {fix drude/transform/inverse} performs
the reverse transformation. For a NVT simulation, with the DCs and
atoms at 300 K and the DPs at 1 K relative to their DC one would use
fix DIRECT all drude/transform/direct
fix NVT1 ATOMS nvt temp 300. 300. 100
fix NVT2 DRUDES nvt temp 1. 1. 20
fix INVERSE all drude/transform/inverse :pre
For our phenol example, the groups would be defined as
group ATOMS type 1 2 3 4 5 # DCs and non-polarizable atoms
group CORES type 1 2 3 # DCs
group DRUDES type 6 7 8 # DPs :pre
Note that with the fixes {drude/transform}, it is not required to
specify {comm_modify vel yes} because the fixes do it anyway (several
times and for the forces also). To avoid the flying ice cube artifact
"(Lamoureux)"_#Lamoureux2, where the atoms progressively freeze and the
center of mass of the whole system drifts faster and faster, the {fix
momentum} can be used. For instance:
fix MOMENTUM all momentum 100 linear 1 1 1 :pre
It is a bit more tricky to run a NPT simulation with Nose-Hoover
barostat and thermostat. First, the volume should be integrated only
once. So the fix for DCs and atoms should be {npt} while the fix for
DPs should be {nvt} (or vice versa). Second, the {fix npt} computes a
global pressure and thus a global temperature whatever the fix group.
We do want the pressure to correspond to the whole system, but we want
the temperature to correspond to the fix group only. We must then use
the {fix_modify} command for this. In the end, the block of
instructions for thermostatting and barostatting will look like
compute TATOMS ATOMS temp
fix DIRECT all drude/transform/direct
fix NPT ATOMS npt temp 300. 300. 100 iso 1. 1. 500
fix_modify NPT temp TATOMS press thermo_press
fix NVT DRUDES nvt temp 1. 1. 20
fix INVERSE all drude/transform/inverse :pre
:line
[Rigid bodies]
You may want to simulate molecules as rigid bodies (but polarizable).
Common cases are water models such as "SWM4-NDP"_#SWM4-NDP, which is a
kind of polarizable TIP4P water. The rigid bodies and the DPs should
be integrated separately, even with the Langevin thermostat. Let us
review the different thermostats and ensemble combinations.
NVT ensemble using Langevin thermostat:
comm_modify vel yes
fix LANG all langevin/drude 300. 100 12435 1. 20 13977
fix RIGID ATOMS rigid/nve/small molecule
fix NVE DRUDES nve :pre
NVT ensemble using Nose-Hoover thermostat:
fix DIRECT all drude/transform/direct
fix RIGID ATOMS rigid/nvt/small molecule temp 300. 300. 100
fix NVT DRUDES nvt temp 1. 1. 20
fix INVERSE all drude/transform/inverse :pre
NPT ensemble with Langevin thermostat:
comm_modify vel yes
fix LANG all langevin/drude 300. 100 12435 1. 20 13977
fix RIGID ATOMS rigid/nph/small molecule iso 1. 1. 500
fix NVE DRUDES nve :pre
NPT ensemble using Nose-Hoover thermostat:
compute TATOM ATOMS temp
fix DIRECT all drude/transform/direct
fix RIGID ATOMS rigid/npt/small molecule temp 300. 300. 100 iso 1. 1. 500
fix_modify RIGID temp TATOM press thermo_press
fix NVT DRUDES nvt temp 1. 1. 20
fix INVERSE all drude/transform/inverse :pre
:line
:link(Lamoureux2)
[(Lamoureux)] Lamoureux and Roux, J Chem Phys, 119, 3025-3039 (2003)
:link(Schroeder)
[(Schroeder)] Schroeder and Steinhauser, J Chem Phys, 133,
154511 (2010).
:link(Jiang2)
[(Jiang)] Jiang, Hardy, Phillips, MacKerell, Schulten, and Roux,
J Phys Chem Lett, 2, 87-92 (2011).
:link(Thole2)
[(Thole)] Chem Phys, 59, 341 (1981).
:link(Noskov2)
[(Noskov)] Noskov, Lamoureux and Roux, J Phys Chem B, 109, 6705 (2005).
:link(SWM4-NDP)
[(SWM4-NDP)] Lamoureux, Harder, Vorobyov, Roux, MacKerell, Chem Phys
Let, 418, 245-249 (2006)

47
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@ -1,47 +0,0 @@
"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Calculate elastic constants :h3
Elastic constants characterize the stiffness of a material. The formal
definition is provided by the linear relation that holds between the
stress and strain tensors in the limit of infinitesimal deformation.
In tensor notation, this is expressed as s_ij = C_ijkl * e_kl, where
the repeated indices imply summation. s_ij are the elements of the
symmetric stress tensor. e_kl are the elements of the symmetric strain
tensor. C_ijkl are the elements of the fourth rank tensor of elastic
constants. In three dimensions, this tensor has 3^4=81 elements. Using
Voigt notation, the tensor can be written as a 6x6 matrix, where C_ij
is now the derivative of s_i w.r.t. e_j. Because s_i is itself a
derivative w.r.t. e_i, it follows that C_ij is also symmetric, with at
most 7*6/2 = 21 distinct elements.
At zero temperature, it is easy to estimate these derivatives by
deforming the simulation box in one of the six directions using the
"change_box"_change_box.html command and measuring the change in the
stress tensor. A general-purpose script that does this is given in the
examples/elastic directory described on the "Examples"_Examples.html
doc page.
Calculating elastic constants at finite temperature is more
challenging, because it is necessary to run a simulation that performs
time averages of differential properties. One way to do this is to
measure the change in average stress tensor in an NVT simulations when
the cell volume undergoes a finite deformation. In order to balance
the systematic and statistical errors in this method, the magnitude of
the deformation must be chosen judiciously, and care must be taken to
fully equilibrate the deformed cell before sampling the stress
tensor. Another approach is to sample the triclinic cell fluctuations
that occur in an NPT simulation. This method can also be slow to
converge and requires careful post-processing "(Shinoda)"_#Shinoda1
:line
:link(Shinoda1)
[(Shinoda)] Shinoda, Shiga, and Mikami, Phys Rev B, 69, 134103 (2004).

419
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@ -1,419 +0,0 @@
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
LAMMPS GitHub tutorial :h3
[written by Stefan Paquay]
:line
This document describes the process of how to use GitHub to integrate
changes or additions you have made to LAMMPS into the official LAMMPS
distribution. It uses the process of updating this very tutorial as
an example to describe the individual steps and options. You need to
be familiar with git and you may want to have a look at the
"Git book"_http://git-scm.com/book/ to reacquaint yourself with some
of the more advanced git features used below.
As of fall 2016, submitting contributions to LAMMPS via pull requests
on GitHub is the preferred option for integrating contributed features
or improvements to LAMMPS, as it significantly reduces the amount of
work required by the LAMMPS developers. Consequently, creating a pull
request will increase your chances to have your contribution included
and will reduce the time until the integration is complete. For more
information on the requirements to have your code included into LAMMPS
please see the "Modify contribute"_Modify_contribute.html doc page.
:line
[Making an account]
First of all, you need a GitHub account. This is fairly simple, just
go to "GitHub"_https://github.com and create an account by clicking
the "Sign up for GitHub" button. Once your account is created, you
can sign in by clicking the button in the top left and filling in your
username or e-mail address and password.
:line
[Forking the repository]
To get changes into LAMMPS, you need to first fork the `lammps/lammps`
repository on GitHub. At the time of writing, {master} is the preferred
target branch. Thus go to "LAMMPS on GitHub"_https://github.com/lammps/lammps
and make sure branch is set to "master", as shown in the figure below.
:c,image(JPG/tutorial_branch.png)
If it is not, use the button to change it to {master}. Once it is, use the
fork button to create a fork.
:c,image(JPG/tutorial_fork.png)
This will create a fork (which is essentially a copy, but uses less
resources) of the LAMMPS repository under your own GitHub account. You
can make changes in this fork and later file {pull requests} to allow
the upstream repository to merge changes from your own fork into the one
we just forked from (or others that were forked from the same repository).
At the same time, you can set things up, so you can include changes from
upstream into your repository and thus keep it in sync with the ongoing
LAMMPS development.
:line
[Adding changes to your own fork]
Additions to the upstream version of LAMMPS are handled using {feature
branches}. For every new feature, a so-called feature branch is
created, which contains only those modification relevant to one specific
feature. For example, adding a single fix would consist of creating a
branch with only the fix header and source file and nothing else. It is
explained in more detail here: "feature branch
workflow"_https://www.atlassian.com/git/tutorials/comparing-workflows/feature-branch-workflow.
[Feature branches]
First of all, create a clone of your version on github on your local
machine via HTTPS:
$ git clone https://github.com/<your user name>/lammps.git <some name> :pre
or, if you have set up your GitHub account for using SSH keys, via SSH:
$ git clone git@github.com:<your user name>/lammps.git :pre
You can find the proper URL by clicking the "Clone or download"-button:
:c,image(JPG/tutorial_https_block.png)
The above command copies ("clones") the git repository to your local
machine to a directory with the name you chose. If none is given, it will
default to "lammps". Typical names are "mylammps" or something similar.
You can use this local clone to make changes and
test them without interfering with the repository on GitHub.
To pull changes from upstream into this copy, you can go to the directory
and use git pull:
$ cd mylammps
$ git checkout master
$ git pull https://github.com/lammps/lammps :pre
You can also add this URL as a remote:
$ git remote add lammps_upstream https://www.github.com/lammps/lammps :pre
At this point, you typically make a feature branch from the updated master
branch for the feature you want to work on. This tutorial contains the
workflow that updated this tutorial, and hence we will call the branch
"github-tutorial-update":
$ git checkout -b github-tutorial-update master :pre
Now that we have changed branches, we can make our changes to our local
repository. Just remember that if you want to start working on another,
unrelated feature, you should switch branches!
[After changes are made]
After everything is done, add the files to the branch and commit them:
$ git add doc/src/Howto_github.txt
$ git add doc/src/JPG/tutorial*.png :pre
IMPORTANT NOTE: Do not use {git commit -a} (or {git add -A}). The -a
flag (or -A flag) will automatically include _all_ modified or new files
and that is rarely the behavior you want. It can easily lead to
accidentally adding unrelated and unwanted changes into the repository.
Instead it is preferable to explicitly use {git add}, {git rm}, {git mv}
for adding, removing, renaming individual files, respectively, and then
{git commit} to finalize the commit. Carefully check all pending
changes with {git status} before committing them. If you find doing
this on the command line too tedious, consider using a GUI, for example
the one included in git distributions written in Tk, i.e. use {git gui}
(on some Linux distributions it may be required to install an additional
package to use it).
After adding all files, the change set can be committed with some
useful message that explains the change.
$ git commit -m 'Finally updated the github tutorial' :pre
After the commit, the changes can be pushed to the same branch on GitHub:
$ git push :pre
Git will ask you for your user name and password on GitHub if you have
not configured anything. If your local branch is not present on GitHub yet,
it will ask you to add it by running
$ git push --set-upstream origin github-tutorial-update :pre
If you correctly type your user name and
password, the feature branch should be added to your fork on GitHub.
If you want to make really sure you push to the right repository
(which is good practice), you can provide it explicitly:
$ git push origin :pre
or using an explicit URL:
$ git push git@github.com:Pakketeretet2/lammps.git :pre
:line
[Filing a pull request]
Up to this point in the tutorial, all changes were to {your} clones of
LAMMPS. Eventually, however, you want this feature to be included into
the official LAMMPS version. To do this, you will want to file a pull
request by clicking on the "New pull request" button:
:c,image(JPG/tutorial_new_pull_request.png)
Make sure that the current branch is set to the correct one, which, in
this case, is "github-tutorial-update". If done correctly, the only
changes you will see are those that were made on this branch.
This will open up a new window that lists changes made to the
repository. If you are just adding new files, there is not much to do,
but I suppose merge conflicts are to be resolved here if there are
changes in existing files. If all changes can automatically be merged,
green text at the top will say so and you can click the "Create pull
request" button, see image.
:c,image(JPG/tutorial_create_new_pull_request1.png)
Before creating the pull request, make sure the short title is accurate
and add a comment with details about your pull request. Here you write
what your modifications do and why they should be incorporated upstream.
Note the checkbox that says "Allow edits from maintainers".
This is checked by default checkbox (although in my version of Firefox, only the checkmark is visible):
:c,image(JPG/tutorial_edits_maintainers.png)
If it is checked, maintainers can immediately add their own edits to the
pull request. This helps the inclusion of your branch significantly, as
simple/trivial changes can be added directly to your pull request branch
by the LAMMPS maintainers. The alternative would be that they make
changes on their own version of the branch and file a reverse pull
request to you. Just leave this box checked unless you have a very good
reason not to.
Now just write some nice comments and click on "Create pull request".
:c,image(JPG/tutorial_create_new_pull_request2.png)
:line
[After filing a pull request]
NOTE: When you submit a pull request (or ask for a pull request) for the
first time, you will receive an invitation to become a LAMMPS project
collaborator. Please accept this invite as being a collaborator will
simplify certain administrative tasks and will probably speed up the
merging of your feature, too.
You will notice that after filing the pull request, some checks are
performed automatically:
:c,image(JPG/tutorial_automated_checks.png)
If all is fine, you will see this:
:c,image(JPG/tutorial_automated_checks_passed.png)
If any of the checks are failing, your pull request will not be
processed, as your changes may break compilation for certain
configurations or may not merge cleanly. It is your responsibility
to remove the reason(s) for the failed test(s). If you need help
with this, please contact the LAMMPS developers by adding a comment
explaining your problems with resolving the failed tests.
A few further interesting things (can) happen to pull requests before
they are included.
[Additional changes]
First of all, any additional changes you push into your branch in your
repository will automatically become part of the pull request:
:c,image(JPG/tutorial_additional_changes.png)
This means you can add changes that should be part of the feature after
filing the pull request, which is useful in case you have forgotten
them, or if a developer has requested that something needs to be changed
before the feature can be accepted into the official LAMMPS version.
After each push, the automated checks are run again.
[Labels]
LAMMPS developers may add labels to your pull request to assign it to
categories (mostly for bookkeeping purposes), but a few of them are
important: needs_work, work_in_progress, test-for-regression, and
full-regression-test. The first two indicate, that your pull request
is not considered to be complete. With "needs_work" the burden is on
exclusively on you; while "work_in_progress" can also mean, that a
LAMMPS developer may want to add changes. Please watch the comments
to the pull requests. The two "test" labels are used to trigger
extended tests before the code is merged. This is sometimes done by
LAMMPS developers, if they suspect that there may be some subtle
side effects from your changes. It is not done by default, because
those tests are very time consuming.
[Reviews]
As of Summer 2018, a pull request needs at least 1 approving review
from a LAMMPS developer with write access to the repository.
In case your changes touch code that certain developers are associated
with, they are auto-requested by the GitHub software. Those associations
are set in the file
".github/CODEOWNERS"_https://github.com/lammps/lammps/blob/master/.github/CODEOWNERS
Thus if you want to be automatically notified to review when anybody
changes files or packages, that you have contributed to LAMMPS, you can
add suitable patterns to that file, or a LAMMPS developer may add you.
Otherwise, you can also manually request reviews from specific developers,
or LAMMPS developers - in their assessment of your pull request - may
determine who else should be reviewing your contribution and add that person.
Through reviews, LAMMPS developers also may request specific changes from you.
If those are not addressed, your pull requests cannot be merged.
[Assignees]
There is an assignee property for pull requests. If the request has not
been reviewed by any developer yet, it is not assigned to anyone. After
revision, a developer can choose to assign it to either a) you, b) a
LAMMPS developer (including him/herself) or c) Axel Kohlmeyer (akohlmey).
Case a) happens if changes are required on your part :ulb,l
Case b) means that at the moment, it is being tested and reviewed by a
LAMMPS developer with the expectation that some changes would be required.
After the review, the developer can choose to implement changes directly
or suggest them to you. :l
Case c) means that the pull request has been assigned to the developer
overseeing the merging of pull requests into the master branch. :ule,l
In this case, Axel assigned the tutorial to Steve:
:c,image(JPG/tutorial_steve_assignee.png)
[Edits from LAMMPS maintainers]
If you allowed edits from maintainers (the default), any LAMMPS
maintainer can add changes to your pull request. In this case, both
Axel and Richard made changes to the tutorial:
:c,image(JPG/tutorial_changes_others.png)
[Reverse pull requests]
Sometimes, however, you might not feel comfortable having other people
push changes into your own branch, or maybe the maintainers are not sure
their idea was the right one. In such a case, they can make changes,
reassign you as the assignee, and file a "reverse pull request", i.e.
file a pull request in your GitHub repository to include changes in the
branch, that you have submitted as a pull request yourself. In that
case, you can choose to merge their changes back into your branch,
possibly make additional changes or corrections and proceed from there.
It looks something like this:
:c,image(JPG/tutorial_reverse_pull_request.png)
For some reason, the highlighted button didn't work in my case, but I
can go to my own repository and merge the pull request from there:
:c,image(JPG/tutorial_reverse_pull_request2.png)
Be sure to check the changes to see if you agree with them by clicking
on the tab button:
:c,image(JPG/tutorial_reverse_pull_request3.png)
In this case, most of it is changes in the markup and a short rewrite of
Axel's explanation of the "git gui" and "git add" commands.
:c,image(JPG/tutorial_reverse_pull_request4.png)
Because the changes are OK with us, we are going to merge by clicking on
"Merge pull request". After a merge it looks like this:
:c,image(JPG/tutorial_reverse_pull_request5.png)
Now, since in the meantime our local text for the tutorial also changed,
we need to pull Axel's change back into our branch, and merge them:
$ git add Howto_github.txt
$ git add JPG/tutorial_reverse_pull_request*.png
$ git commit -m "Updated text and images on reverse pull requests"
$ git pull :pre
In this case, the merge was painless because git could auto-merge:
:c,image(JPG/tutorial_reverse_pull_request6.png)
With Axel's changes merged in and some final text updates, our feature
branch is now perfect as far as we are concerned, so we are going to
commit and push again:
$ git add Howto_github.txt
$ git add JPG/tutorial_reverse_pull_request6.png
$ git commit -m "Merged Axel's suggestions and updated text"
$ git push git@github.com:Pakketeretet2/lammps :pre
This merge also shows up on the lammps GitHub page:
:c,image(JPG/tutorial_reverse_pull_request7.png)
:line
[After a merge]
When everything is fine, the feature branch is merged into the master branch:
:c,image(JPG/tutorial_merged.png)
Now one question remains: What to do with the feature branch that got
merged into upstream?
It is in principle safe to delete them from your own fork. This helps
keep it a bit more tidy. Note that you first have to switch to another
branch!
$ git checkout master
$ git pull master
$ git branch -d github-tutorial-update :pre
If you do not pull first, it is not really a problem but git will warn
you at the next statement that you are deleting a local branch that
was not yet fully merged into HEAD. This is because git does not yet
know your branch just got merged into LAMMPS upstream. If you
first delete and then pull, everything should still be fine.
Finally, if you delete the branch locally, you might want to push this
to your remote(s) as well:
$ git push origin :github-tutorial-update :pre
[Recent changes in the workflow]
Some changes to the workflow are not captured in this tutorial. For
example, in addition to the master branch, to which all new features
should be submitted, there is now also an "unstable" and a "stable"
branch; these have the same content as "master", but are only updated
after a patch release or stable release was made.
Furthermore, the naming of the patches now follow the pattern
"patch_<Day><Month><Year>" to simplify comparisons between releases.
Finally, all patches and submissions are subject to automatic testing
and code checks to make sure they at the very least compile.
A discussion of the LAMMPS developer GitHub workflow can be found in the file
"doc/github-development-workflow.md"_https://github.com/lammps/lammps/blob/master/doc/github-development-workflow.md

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Granular models :h3
Granular system are composed of spherical particles with a diameter,
as opposed to point particles. This means they have an angular
velocity and torque can be imparted to them to cause them to rotate.
To run a simulation of a granular model, you will want to use
the following commands:
"atom_style sphere"_atom_style.html
"fix nve/sphere"_fix_nve_sphere.html
"fix gravity"_fix_gravity.html :ul
This compute
"compute erotate/sphere"_compute_erotate_sphere.html :ul
calculates rotational kinetic energy which can be "output with
thermodynamic info"_Howto_output.html.
Use one of these 3 pair potentials, which compute forces and torques
between interacting pairs of particles:
"pair_style"_pair_style.html gran/history
"pair_style"_pair_style.html gran/no_history
"pair_style"_pair_style.html gran/hertzian :ul
These commands implement fix options specific to granular systems:
"fix freeze"_fix_freeze.html
"fix pour"_fix_pour.html
"fix viscous"_fix_viscous.html
"fix wall/gran"_fix_wall_gran.html :ul
The fix style {freeze} zeroes both the force and torque of frozen
atoms, and should be used for granular system instead of the fix style
{setforce}.
For computational efficiency, you can eliminate needless pairwise
computations between frozen atoms by using this command:
"neigh_modify"_neigh_modify.html exclude :ul
NOTE: By default, for 2d systems, granular particles are still modeled
as 3d spheres, not 2d discs (circles), meaning their moment of inertia
will be the same as in 3d. If you wish to model granular particles in
2d as 2d discs, see the note on this topic on the "Howto 2d"_Howto_2d.html
doc page, where 2d simulations are discussed.

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Calculate thermal conductivity :h3
The thermal conductivity kappa of a material can be measured in at
least 4 ways using various options in LAMMPS. See the examples/KAPPA
directory for scripts that implement the 4 methods discussed here for
a simple Lennard-Jones fluid model. Also, see the "Howto
viscosity"_Howto_viscosity.html doc page for an analogous discussion
for viscosity.
The thermal conductivity tensor kappa is a measure of the propensity
of a material to transmit heat energy in a diffusive manner as given
by Fourier's law
J = -kappa grad(T)
where J is the heat flux in units of energy per area per time and
grad(T) is the spatial gradient of temperature. The thermal
conductivity thus has units of energy per distance per time per degree
K and is often approximated as an isotropic quantity, i.e. as a
scalar.
The first method is to setup two thermostatted regions at opposite
ends of a simulation box, or one in the middle and one at the end of a
periodic box. By holding the two regions at different temperatures
with a "thermostatting fix"_Howto_thermostat.html, the energy added to
the hot region should equal the energy subtracted from the cold region
and be proportional to the heat flux moving between the regions. See
the papers by "Ikeshoji and Hafskjold"_#howto-Ikeshoji and
"Wirnsberger et al"_#howto-Wirnsberger for details of this idea. Note
that thermostatting fixes such as "fix nvt"_fix_nh.html, "fix
langevin"_fix_langevin.html, and "fix
temp/rescale"_fix_temp_rescale.html store the cumulative energy they
add/subtract.
Alternatively, as a second method, the "fix heat"_fix_heat.html or
"fix ehex"_fix_ehex.html commands can be used in place of thermostats
on each of two regions to add/subtract specified amounts of energy to
both regions. In both cases, the resulting temperatures of the two
regions can be monitored with the "compute temp/region" command and
the temperature profile of the intermediate region can be monitored
with the "fix ave/chunk"_fix_ave_chunk.html and "compute
ke/atom"_compute_ke_atom.html commands.
The third method is to perform a reverse non-equilibrium MD simulation
using the "fix thermal/conductivity"_fix_thermal_conductivity.html
command which implements the rNEMD algorithm of Muller-Plathe.
Kinetic energy is swapped between atoms in two different layers of the
simulation box. This induces a temperature gradient between the two
layers which can be monitored with the "fix
ave/chunk"_fix_ave_chunk.html and "compute
ke/atom"_compute_ke_atom.html commands. The fix tallies the
cumulative energy transfer that it performs. See the "fix
thermal/conductivity"_fix_thermal_conductivity.html command for
details.
The fourth method is based on the Green-Kubo (GK) formula which
relates the ensemble average of the auto-correlation of the heat flux
to kappa. The heat flux can be calculated from the fluctuations of
per-atom potential and kinetic energies and per-atom stress tensor in
a steady-state equilibrated simulation. This is in contrast to the
two preceding non-equilibrium methods, where energy flows continuously
between hot and cold regions of the simulation box.
The "compute heat/flux"_compute_heat_flux.html command can calculate
the needed heat flux and describes how to implement the Green_Kubo
formalism using additional LAMMPS commands, such as the "fix
ave/correlate"_fix_ave_correlate.html command to calculate the needed
auto-correlation. See the doc page for the "compute
heat/flux"_compute_heat_flux.html command for an example input script
that calculates the thermal conductivity of solid Ar via the GK
formalism.
:line
:link(howto-Ikeshoji)
[(Ikeshoji)] Ikeshoji and Hafskjold, Molecular Physics, 81, 251-261
(1994).
:link(howto-Wirnsberger)
[(Wirnsberger)] Wirnsberger, Frenkel, and Dellago, J Chem Phys, 143, 124104
(2015).

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Library interface to LAMMPS :h3
As described on the "Build basics"_Build_basics.html doc page, LAMMPS
can be built as a library, so that it can be called by another code,
used in a "coupled manner"_Howto_couple.html with other codes, or
driven through a "Python interface"_Python_head.html.
All of these methodologies use a C-style interface to LAMMPS that is
provided in the files src/library.cpp and src/library.h. The
functions therein have a C-style argument list, but contain C++ code
you could write yourself in a C++ application that was invoking LAMMPS
directly. The C++ code in the functions illustrates how to invoke
internal LAMMPS operations. Note that LAMMPS classes are defined
within a LAMMPS namespace (LAMMPS_NS) if you use them from another C++
application.
The examples/COUPLE and python/examples directories have example C++
and C and Python codes which show how a driver code can link to LAMMPS
as a library, run LAMMPS on a subset of processors, grab data from
LAMMPS, change it, and put it back into LAMMPS.
Thread-safety :h4
LAMMPS has not initially been conceived as a thread-safe program, but
over the years changes have been applied to replace operations that
collide with creating multiple LAMMPS instances from multiple-threads
of the same process with thread-safe alternatives. This primarily
applies to the core LAMMPS code and less so on add-on packages, especially
when those packages require additional code in the {lib} folder,
interface LAMMPS to Fortran libraries, or the code uses static variables
(like the USER-COLVARS package.
Another major issue to deal with is to correctly handle MPI. Creating
a LAMMPS instance requires passing an MPI communicator, or it assumes
the MPI_COMM_WORLD communicator, which spans all MPI processor ranks.
When creating multiple LAMMPS object instances from different threads,
this communicator has to be different for each thread or else collisions
can happen, or it has to be guaranteed, that only one thread at a time
is active. MPI communicators, however, are not a problem, if LAMMPS is
compiled with the MPI STUBS library, which implies that there is no MPI
communication and only 1 MPI rank.
Provided APIs :h4
The file src/library.cpp contains the following functions for creating
and destroying an instance of LAMMPS and sending it commands to
execute. See the documentation in the src/library.cpp file for
details.
NOTE: You can write code for additional functions as needed to define
how your code talks to LAMMPS and add them to src/library.cpp and
src/library.h, as well as to the "Python interface"_Python_head.html.
The added functions can access or change any internal LAMMPS data you
wish.
void lammps_open(int, char **, MPI_Comm, void **)
void lammps_open_no_mpi(int, char **, void **)
void lammps_close(void *)
int lammps_version(void *)
void lammps_file(void *, char *)
char *lammps_command(void *, char *)
void lammps_commands_list(void *, int, char **)
void lammps_commands_string(void *, char *)
void lammps_free(void *) :pre
The lammps_open() function is used to initialize LAMMPS, passing in a
list of strings as if they were "command-line
arguments"_Run_options.html when LAMMPS is run in stand-alone mode
from the command line, and a MPI communicator for LAMMPS to run under.
It returns a ptr to the LAMMPS object that is created, and which is
used in subsequent library calls. The lammps_open() function can be
called multiple times, to create multiple instances of LAMMPS.
LAMMPS will run on the set of processors in the communicator. This
means the calling code can run LAMMPS on all or a subset of
processors. For example, a wrapper script might decide to alternate
between LAMMPS and another code, allowing them both to run on all the
processors. Or it might allocate half the processors to LAMMPS and
half to the other code and run both codes simultaneously before
syncing them up periodically. Or it might instantiate multiple
instances of LAMMPS to perform different calculations.
The lammps_open_no_mpi() function is similar except that no MPI
communicator is passed from the caller. Instead, MPI_COMM_WORLD is
used to instantiate LAMMPS, and MPI is initialized if necessary.
The lammps_close() function is used to shut down an instance of LAMMPS
and free all its memory.
The lammps_version() function can be used to determined the specific
version of the underlying LAMMPS code. This is particularly useful
when loading LAMMPS as a shared library via dlopen(). The code using
the library interface can than use this information to adapt to
changes to the LAMMPS command syntax between versions. The returned
LAMMPS version code is an integer (e.g. 2 Sep 2015 results in
20150902) that grows with every new LAMMPS version.
The lammps_file(), lammps_command(), lammps_commands_list(), and
lammps_commands_string() functions are used to pass one or more
commands to LAMMPS to execute, the same as if they were coming from an
input script.
Via these functions, the calling code can read or generate a series of
LAMMPS commands one or multiple at a time and pass it through the library
interface to setup a problem and then run it in stages. The caller
can interleave the command function calls with operations it performs,
calls to extract information from or set information within LAMMPS, or
calls to another code's library.
The lammps_file() function passes the filename of an input script.
The lammps_command() function passes a single command as a string.
The lammps_commands_list() function passes multiple commands in a
char** list. In both lammps_command() and lammps_commands_list(),
individual commands may or may not have a trailing newline. The
lammps_commands_string() function passes multiple commands
concatenated into one long string, separated by newline characters.
In both lammps_commands_list() and lammps_commands_string(), a single
command can be spread across multiple lines, if the last printable
character of all but the last line is "&", the same as if the lines
appeared in an input script.
The lammps_free() function is a clean-up function to free memory that
the library allocated previously via other function calls. See
comments in src/library.cpp file for which other functions need this
clean-up.
The file src/library.cpp also contains these functions for extracting
information from LAMMPS and setting value within LAMMPS. Again, see
the documentation in the src/library.cpp file for details, including
which quantities can be queried by name:
int lammps_extract_setting(void *, char *)
void *lammps_extract_global(void *, char *)
void lammps_extract_box(void *, double *, double *,
double *, double *, double *, int *, int *)
void *lammps_extract_atom(void *, char *)
void *lammps_extract_compute(void *, char *, int, int)
void *lammps_extract_fix(void *, char *, int, int, int, int)
void *lammps_extract_variable(void *, char *, char *) :pre
The extract_setting() function returns info on the size
of data types (e.g. 32-bit or 64-bit atom IDs) used
by the LAMMPS executable (a compile-time choice).
The other extract functions return a pointer to various global or
per-atom quantities stored in LAMMPS or to values calculated by a
compute, fix, or variable. The pointer returned by the
extract_global() function can be used as a permanent reference to a
value which may change. For the extract_atom() method, see the
extract() method in the src/atom.cpp file for a list of valid per-atom
properties. New names could easily be added if the property you want
is not listed. For the other extract functions, the underlying
storage may be reallocated as LAMMPS runs, so you need to re-call the
function to assure a current pointer or returned value(s).
double lammps_get_thermo(void *, char *)
int lammps_get_natoms(void *) :pre
int lammps_set_variable(void *, char *, char *)
void lammps_reset_box(void *, double *, double *, double, double, double) :pre
The lammps_get_thermo() function returns the current value of a thermo
keyword as a double precision value.
The lammps_get_natoms() function returns the total number of atoms in
the system and can be used by the caller to allocate memory for the
lammps_gather_atoms() and lammps_scatter_atoms() functions.
The lammps_set_variable() function can set an existing string-style
variable to a new string value, so that subsequent LAMMPS commands can
access the variable.
The lammps_reset_box() function resets the size and shape of the
simulation box, e.g. as part of restoring a previously extracted and
saved state of a simulation.
void lammps_gather_atoms(void *, char *, int, int, void *)
void lammps_gather_atoms_concat(void *, char *, int, int, void *)
void lammps_gather_atoms_subset(void *, char *, int, int, int, int *, void *)
void lammps_scatter_atoms(void *, char *, int, int, void *)
void lammps_scatter_atoms_subset(void *, char *, int, int, int, int *, void *) :pre
The gather functions collect peratom info of the requested type (atom
coords, atom types, forces, etc) from all processors, and returns the
same vector of values to each calling processor. The scatter
functions do the inverse. They distribute a vector of peratom values,
passed by all calling processors, to individual atoms, which may be
owned by different processors.
IMPORTANT NOTE: These functions are not compatible with the
-DLAMMPS_BIGBIG setting when compiling LAMMPS. Dummy functions
that result in an error message and abort will be substituted
instead of resulting in random crashes and memory corruption.
The lammps_gather_atoms() function does this for all N atoms in the
system, ordered by atom ID, from 1 to N. The
lammps_gather_atoms_concat() function does it for all N atoms, but
simply concatenates the subset of atoms owned by each processor. The
resulting vector is not ordered by atom ID. Atom IDs can be requested
by the same function if the caller needs to know the ordering. The
lammps_gather_subset() function allows the caller to request values
for only a subset of atoms (identified by ID).
For all 3 gather function, per-atom image flags can be retrieved in 2 ways.
If the count is specified as 1, they are returned
in a packed format with all three image flags stored in a single integer.
If the count is specified as 3, the values are unpacked into xyz flags
by the library before returning them.
The lammps_scatter_atoms() function takes a list of values for all N
atoms in the system, ordered by atom ID, from 1 to N, and assigns
those values to each atom in the system. The
lammps_scatter_atoms_subset() function takes a subset of IDs as an
argument and only scatters those values to the owning atoms.
void lammps_create_atoms(void *, int, tagint *, int *, double *, double *,
imageint *, int) :pre
The lammps_create_atoms() function takes a list of N atoms as input
with atom types and coords (required), an optionally atom IDs and
velocities and image flags. It uses the coords of each atom to assign
it as a new atom to the processor that owns it. This function is
useful to add atoms to a simulation or (in tandem with
lammps_reset_box()) to restore a previously extracted and saved state
of a simulation. Additional properties for the new atoms can then be
assigned via the lammps_scatter_atoms() or lammps_extract_atom()
functions.

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"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Manifolds (surfaces) :h3
[Overview:]
This doc page is not about a LAMMPS input script command, but about
manifolds, which are generalized surfaces, as defined and used by the
USER-MANIFOLD package, to track particle motion on the manifolds. See
the src/USER-MANIFOLD/README file for more details about the package
and its commands.
Below is a list of currently supported manifolds by the USER-MANIFOLD
package, their parameters and a short description of them. The
parameters listed here are in the same order as they should be passed
to the relevant fixes.
{manifold} @ {parameters} @ {equation} @ {description}
cylinder @ R @ x^2 + y^2 - R^2 = 0 @ Cylinder along z-axis, axis going through (0,0,0)
cylinder_dent @ R l a @ x^2 + y^2 - r(z)^2 = 0, r(x) = R if | z | > l, r(z) = R - a*(1 + cos(z/l))/2 otherwise @ A cylinder with a dent around z = 0
dumbbell @ a A B c @ -( x^2 + y^2 ) + (a^2 - z^2/c^2) * ( 1 + (A*sin(B*z^2))^4) = 0 @ A dumbbell
ellipsoid @ a b c @ (x/a)^2 + (y/b)^2 + (z/c)^2 = 0 @ An ellipsoid
gaussian_bump @ A l rc1 rc2 @ if( x < rc1) -z + A * exp( -x^2 / (2 l^2) ); else if( x < rc2 ) -z + a + b*x + c*x^2 + d*x^3; else z @ A Gaussian bump at x = y = 0, smoothly tapered to a flat plane z = 0.
plane @ a b c x0 y0 z0 @ a*(x-x0) + b*(y-y0) + c*(z-z0) = 0 @ A plane with normal (a,b,c) going through point (x0,y0,z0)
plane_wiggle @ a w @ z - a*sin(w*x) = 0 @ A plane with a sinusoidal modulation on z along x.
sphere @ R @ x^2 + y^2 + z^2 - R^2 = 0 @ A sphere of radius R
supersphere @ R q @ | x |^q + | y |^q + | z |^q - R^q = 0 @ A supersphere of hyperradius R
spine @ a, A, B, B2, c @ -(x^2 + y^2) + (a^2 - z^2/f(z)^2)*(1 + (A*sin(g(z)*z^2))^4), f(z) = c if z > 0, 1 otherwise; g(z) = B if z > 0, B2 otherwise @ An approximation to a dendritic spine
spine_two @ a, A, B, B2, c @ -(x^2 + y^2) + (a^2 - z^2/f(z)^2)*(1 + (A*sin(g(z)*z^2))^2), f(z) = c if z > 0, 1 otherwise; g(z) = B if z > 0, B2 otherwise @ Another approximation to a dendritic spine
thylakoid @ wB LB lB @ Various, see "(Paquay)"_#Paquay1 @ A model grana thylakoid consisting of two block-like compartments connected by a bridge of width wB, length LB and taper length lB
torus @ R r @ (R - sqrt( x^2 + y^2 ) )^2 + z^2 - r^2 @ A torus with large radius R and small radius r, centered on (0,0,0) :tb(s=@)
:link(Paquay1)
[(Paquay)] Paquay and Kusters, Biophys. J., 110, 6, (2016).
preprint available at "arXiv:1411.3019"_http://arxiv.org/abs/1411.3019/.

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Run multiple simulations from one input script :h3
This can be done in several ways. See the documentation for
individual commands for more details on how these examples work.
If "multiple simulations" means continue a previous simulation for
more timesteps, then you simply use the "run"_run.html command
multiple times. For example, this script
units lj
atom_style atomic
read_data data.lj
run 10000
run 10000
run 10000
run 10000
run 10000 :pre
would run 5 successive simulations of the same system for a total of
50,000 timesteps.
If you wish to run totally different simulations, one after the other,
the "clear"_clear.html command can be used in between them to
re-initialize LAMMPS. For example, this script
units lj
atom_style atomic
read_data data.lj
run 10000
clear
units lj
atom_style atomic
read_data data.lj.new
run 10000 :pre
would run 2 independent simulations, one after the other.
For large numbers of independent simulations, you can use
"variables"_variable.html and the "next"_next.html and
"jump"_jump.html commands to loop over the same input script
multiple times with different settings. For example, this
script, named in.polymer
variable d index run1 run2 run3 run4 run5 run6 run7 run8
shell cd $d
read_data data.polymer
run 10000
shell cd ..
clear
next d
jump in.polymer :pre
would run 8 simulations in different directories, using a data.polymer
file in each directory. The same concept could be used to run the
same system at 8 different temperatures, using a temperature variable
and storing the output in different log and dump files, for example
variable a loop 8
variable t index 0.8 0.85 0.9 0.95 1.0 1.05 1.1 1.15
log log.$a
read data.polymer
velocity all create $t 352839
fix 1 all nvt $t $t 100.0
dump 1 all atom 1000 dump.$a
run 100000
clear
next t
next a
jump in.polymer :pre
All of the above examples work whether you are running on 1 or
multiple processors, but assumed you are running LAMMPS on a single
partition of processors. LAMMPS can be run on multiple partitions via
the "-partition command-line switch"_Run_options.html.
In the last 2 examples, if LAMMPS were run on 3 partitions, the same
scripts could be used if the "index" and "loop" variables were
replaced with {universe}-style variables, as described in the
"variable"_variable.html command. Also, the "next t" and "next a"
commands would need to be replaced with a single "next a t" command.
With these modifications, the 8 simulations of each script would run
on the 3 partitions one after the other until all were finished.
Initially, 3 simulations would be started simultaneously, one on each
partition. When one finished, that partition would then start
the 4th simulation, and so forth, until all 8 were completed.

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
NEMD simulations :h3
Non-equilibrium molecular dynamics or NEMD simulations are typically
used to measure a fluid's rheological properties such as viscosity.
In LAMMPS, such simulations can be performed by first setting up a
non-orthogonal simulation box (see the preceding Howto section).
A shear strain can be applied to the simulation box at a desired
strain rate by using the "fix deform"_fix_deform.html command. The
"fix nvt/sllod"_fix_nvt_sllod.html command can be used to thermostat
the sheared fluid and integrate the SLLOD equations of motion for the
system. Fix nvt/sllod uses "compute
temp/deform"_compute_temp_deform.html to compute a thermal temperature
by subtracting out the streaming velocity of the shearing atoms. The
velocity profile or other properties of the fluid can be monitored via
the "fix ave/chunk"_fix_ave_chunk.html command.
NOTE: A recent (2017) book by "(Daivis and Todd)"_#Daivis-nemd
discusses use of the SLLOD method and non-equilibrium MD (NEMD)
thermostatting generally, for both simple and complex fluids,
e.g. molecular systems. The latter can be tricky to do correctly.
As discussed in the previous section on non-orthogonal simulation
boxes, the amount of tilt or skew that can be applied is limited by
LAMMPS for computational efficiency to be 1/2 of the parallel box
length. However, "fix deform"_fix_deform.html can continuously strain
a box by an arbitrary amount. As discussed in the "fix
deform"_fix_deform.html command, when the tilt value reaches a limit,
the box is flipped to the opposite limit which is an equivalent tiling
of periodic space. The strain rate can then continue to change as
before. In a long NEMD simulation these box re-shaping events may
occur many times.
In a NEMD simulation, the "remap" option of "fix
deform"_fix_deform.html should be set to "remap v", since that is what
"fix nvt/sllod"_fix_nvt_sllod.html assumes to generate a velocity
profile consistent with the applied shear strain rate.
An alternative method for calculating viscosities is provided via the
"fix viscosity"_fix_viscosity.html command.
NEMD simulations can also be used to measure transport properties of a fluid
through a pore or channel. Simulations of steady-state flow can be performed
using the "fix flow/gauss"_fix_flow_gauss.html command.
:line
:link(Daivis-nemd)
[(Daivis and Todd)] Daivis and Todd, Nonequilibrium Molecular Dynamics (book),
Cambridge University Press, https://doi.org/10.1017/9781139017848, (2017).

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Output from LAMMPS (thermo, dumps, computes, fixes, variables) :h3
There are four basic kinds of LAMMPS output:
"Thermodynamic output"_thermo_style.html, which is a list
of quantities printed every few timesteps to the screen and logfile. :ulb,l
"Dump files"_dump.html, which contain snapshots of atoms and various
per-atom values and are written at a specified frequency. :l
Certain fixes can output user-specified quantities to files: "fix
ave/time"_fix_ave_time.html for time averaging, "fix
ave/chunk"_fix_ave_chunk.html for spatial or other averaging, and "fix
print"_fix_print.html for single-line output of
"variables"_variable.html. Fix print can also output to the
screen. :l
"Restart files"_restart.html. :l
:ule
A simulation prints one set of thermodynamic output and (optionally)
restart files. It can generate any number of dump files and fix
output files, depending on what "dump"_dump.html and "fix"_fix.html
commands you specify.
As discussed below, LAMMPS gives you a variety of ways to determine
what quantities are computed and printed when the thermodynamics,
dump, or fix commands listed above perform output. Throughout this
discussion, note that users can also "add their own computes and fixes
to LAMMPS"_Modify.html which can then generate values that can then be
output with these commands.
The following sub-sections discuss different LAMMPS command related
to output and the kind of data they operate on and produce:
"Global/per-atom/local data"_#global
"Scalar/vector/array data"_#scalar
"Thermodynamic output"_#thermo
"Dump file output"_#dump
"Fixes that write output files"_#fixoutput
"Computes that process output quantities"_#computeoutput
"Fixes that process output quantities"_#fixprocoutput
"Computes that generate values to output"_#compute
"Fixes that generate values to output"_#fix
"Variables that generate values to output"_#variable
"Summary table of output options and data flow between commands"_#table :ul
Global/per-atom/local data :h4,link(global)
Various output-related commands work with three different styles of
data: global, per-atom, or local. A global datum is one or more
system-wide values, e.g. the temperature of the system. A per-atom
datum is one or more values per atom, e.g. the kinetic energy of each
atom. Local datums are calculated by each processor based on the
atoms it owns, but there may be zero or more per atom, e.g. a list of
bond distances.
Scalar/vector/array data :h4,link(scalar)
Global, per-atom, and local datums can each come in three kinds: a
single scalar value, a vector of values, or a 2d array of values. The
doc page for a "compute" or "fix" or "variable" that generates data
will specify both the style and kind of data it produces, e.g. a
per-atom vector.
When a quantity is accessed, as in many of the output commands
discussed below, it can be referenced via the following bracket
notation, where ID in this case is the ID of a compute. The leading
"c_" would be replaced by "f_" for a fix, or "v_" for a variable:
c_ID | entire scalar, vector, or array
c_ID\[I\] | one element of vector, one column of array
c_ID\[I\]\[J\] | one element of array :tb(s=|)
In other words, using one bracket reduces the dimension of the data
once (vector -> scalar, array -> vector). Using two brackets reduces
the dimension twice (array -> scalar). Thus a command that uses
scalar values as input can typically also process elements of a vector
or array.
Thermodynamic output :h4,link(thermo)
The frequency and format of thermodynamic output is set by the
"thermo"_thermo.html, "thermo_style"_thermo_style.html, and
"thermo_modify"_thermo_modify.html commands. The
"thermo_style"_thermo_style.html command also specifies what values
are calculated and written out. Pre-defined keywords can be specified
(e.g. press, etotal, etc). Three additional kinds of keywords can
also be specified (c_ID, f_ID, v_name), where a "compute"_compute.html
or "fix"_fix.html or "variable"_variable.html provides the value to be
output. In each case, the compute, fix, or variable must generate
global values for input to the "thermo_style custom"_dump.html
command.
Note that thermodynamic output values can be "extensive" or
"intensive". The former scale with the number of atoms in the system
(e.g. total energy), the latter do not (e.g. temperature). The
setting for "thermo_modify norm"_thermo_modify.html determines whether
extensive quantities are normalized or not. Computes and fixes
produce either extensive or intensive values; see their individual doc
pages for details. "Equal-style variables"_variable.html produce only
intensive values; you can include a division by "natoms" in the
formula if desired, to make an extensive calculation produce an
intensive result.
Dump file output :h4,link(dump)
Dump file output is specified by the "dump"_dump.html and
"dump_modify"_dump_modify.html commands. There are several
pre-defined formats (dump atom, dump xtc, etc).
There is also a "dump custom"_dump.html format where the user
specifies what values are output with each atom. Pre-defined atom
attributes can be specified (id, x, fx, etc). Three additional kinds
of keywords can also be specified (c_ID, f_ID, v_name), where a
"compute"_compute.html or "fix"_fix.html or "variable"_variable.html
provides the values to be output. In each case, the compute, fix, or
variable must generate per-atom values for input to the "dump
custom"_dump.html command.
There is also a "dump local"_dump.html format where the user specifies
what local values to output. A pre-defined index keyword can be
specified to enumerate the local values. Two additional kinds of
keywords can also be specified (c_ID, f_ID), where a
"compute"_compute.html or "fix"_fix.html or "variable"_variable.html
provides the values to be output. In each case, the compute or fix
must generate local values for input to the "dump local"_dump.html
command.
Fixes that write output files :h4,link(fixoutput)
Several fixes take various quantities as input and can write output
files: "fix ave/time"_fix_ave_time.html, "fix
ave/chunk"_fix_ave_chunk.html, "fix ave/histo"_fix_ave_histo.html,
"fix ave/correlate"_fix_ave_correlate.html, and "fix
print"_fix_print.html.
The "fix ave/time"_fix_ave_time.html command enables direct output to
a file and/or time-averaging of global scalars or vectors. The user
specifies one or more quantities as input. These can be global
"compute"_compute.html values, global "fix"_fix.html values, or
"variables"_variable.html of any style except the atom style which
produces per-atom values. Since a variable can refer to keywords used
by the "thermo_style custom"_thermo_style.html command (like temp or
press) and individual per-atom values, a wide variety of quantities
can be time averaged and/or output in this way. If the inputs are one
or more scalar values, then the fix generate a global scalar or vector
of output. If the inputs are one or more vector values, then the fix
generates a global vector or array of output. The time-averaged
output of this fix can also be used as input to other output commands.
The "fix ave/chunk"_fix_ave_chunk.html command enables direct output
to a file of chunk-averaged per-atom quantities like those output in
dump files. Chunks can represent spatial bins or other collections of
atoms, e.g. individual molecules. The per-atom quantities can be atom
density (mass or number) or atom attributes such as position,
velocity, force. They can also be per-atom quantities calculated by a
"compute"_compute.html, by a "fix"_fix.html, or by an atom-style
"variable"_variable.html. The chunk-averaged output of this fix can
also be used as input to other output commands.
The "fix ave/histo"_fix_ave_histo.html command enables direct output
to a file of histogrammed quantities, which can be global or per-atom
or local quantities. The histogram output of this fix can also be
used as input to other output commands.
The "fix ave/correlate"_fix_ave_correlate.html command enables direct
output to a file of time-correlated quantities, which can be global
values. The correlation matrix output of this fix can also be used as
input to other output commands.
The "fix print"_fix_print.html command can generate a line of output
written to the screen and log file or to a separate file, periodically
during a running simulation. The line can contain one or more
"variable"_variable.html values for any style variable except the
vector or atom styles). As explained above, variables themselves can
contain references to global values generated by "thermodynamic
keywords"_thermo_style.html, "computes"_compute.html,
"fixes"_fix.html, or other "variables"_variable.html, or to per-atom
values for a specific atom. Thus the "fix print"_fix_print.html
command is a means to output a wide variety of quantities separate
from normal thermodynamic or dump file output.
Computes that process output quantities :h4,link(computeoutput)
The "compute reduce"_compute_reduce.html and "compute
reduce/region"_compute_reduce.html commands take one or more per-atom
or local vector quantities as inputs and "reduce" them (sum, min, max,
ave) to scalar quantities. These are produced as output values which
can be used as input to other output commands.
The "compute slice"_compute_slice.html command take one or more global
vector or array quantities as inputs and extracts a subset of their
values to create a new vector or array. These are produced as output
values which can be used as input to other output commands.
The "compute property/atom"_compute_property_atom.html command takes a
list of one or more pre-defined atom attributes (id, x, fx, etc) and
stores the values in a per-atom vector or array. These are produced
as output values which can be used as input to other output commands.
The list of atom attributes is the same as for the "dump
custom"_dump.html command.
The "compute property/local"_compute_property_local.html command takes
a list of one or more pre-defined local attributes (bond info, angle
info, etc) and stores the values in a local vector or array. These
are produced as output values which can be used as input to other
output commands.
Fixes that process output quantities :h4,link(fixprocoutput)
The "fix vector"_fix_vector.html command can create global vectors as
output from global scalars as input, accumulating them one element at
a time.
The "fix ave/atom"_fix_ave_atom.html command performs time-averaging
of per-atom vectors. The per-atom quantities can be atom attributes
such as position, velocity, force. They can also be per-atom
quantities calculated by a "compute"_compute.html, by a
"fix"_fix.html, or by an atom-style "variable"_variable.html. The
time-averaged per-atom output of this fix can be used as input to
other output commands.
The "fix store/state"_fix_store_state.html command can archive one or
more per-atom attributes at a particular time, so that the old values
can be used in a future calculation or output. The list of atom
attributes is the same as for the "dump custom"_dump.html command,
including per-atom quantities calculated by a "compute"_compute.html,
by a "fix"_fix.html, or by an atom-style "variable"_variable.html.
The output of this fix can be used as input to other output commands.
Computes that generate values to output :h4,link(compute)
Every "compute"_compute.html in LAMMPS produces either global or
per-atom or local values. The values can be scalars or vectors or
arrays of data. These values can be output using the other commands
described in this section. The doc page for each compute command
describes what it produces. Computes that produce per-atom or local
values have the word "atom" or "local" in their style name. Computes
without the word "atom" or "local" produce global values.
Fixes that generate values to output :h4,link(fix)
Some "fixes"_fix.html in LAMMPS produces either global or per-atom or
local values which can be accessed by other commands. The values can
be scalars or vectors or arrays of data. These values can be output
using the other commands described in this section. The doc page for
each fix command tells whether it produces any output quantities and
describes them.
Variables that generate values to output :h4,link(variable)
"Variables"_variable.html defined in an input script can store one or
more strings. But equal-style, vector-style, and atom-style or
atomfile-style variables generate a global scalar value, global vector
or values, or a per-atom vector, respectively, when accessed. The
formulas used to define these variables can contain references to the
thermodynamic keywords and to global and per-atom data generated by
computes, fixes, and other variables. The values generated by
variables can be used as input to and thus output by the other
commands described in this section.
Summary table of output options and data flow between commands :h4,link(table)
This table summarizes the various commands that can be used for
generating output from LAMMPS. Each command produces output data of
some kind and/or writes data to a file. Most of the commands can take
data from other commands as input. Thus you can link many of these
commands together in pipeline form, where data produced by one command
is used as input to another command and eventually written to the
screen or to a file. Note that to hook two commands together the
output and input data types must match, e.g. global/per-atom/local
data and scalar/vector/array data.
Also note that, as described above, when a command takes a scalar as
input, that could be an element of a vector or array. Likewise a
vector input could be a column of an array.
Command: Input: Output:
"thermo_style custom"_thermo_style.html: global scalars: screen, log file:
"dump custom"_dump.html: per-atom vectors: dump file:
"dump local"_dump.html: local vectors: dump file:
"fix print"_fix_print.html: global scalar from variable: screen, file:
"print"_print.html: global scalar from variable: screen:
"computes"_compute.html: N/A: global/per-atom/local scalar/vector/array:
"fixes"_fix.html: N/A: global/per-atom/local scalar/vector/array:
"variables"_variable.html: global scalars and vectors, per-atom vectors: global scalar and vector, per-atom vector:
"compute reduce"_compute_reduce.html: per-atom/local vectors: global scalar/vector:
"compute slice"_compute_slice.html: global vectors/arrays: global vector/array:
"compute property/atom"_compute_property_atom.html: per-atom vectors: per-atom vector/array:
"compute property/local"_compute_property_local.html: local vectors: local vector/array:
"fix vector"_fix_vector.html: global scalars: global vector:
"fix ave/atom"_fix_ave_atom.html: per-atom vectors: per-atom vector/array:
"fix ave/time"_fix_ave_time.html: global scalars/vectors: global scalar/vector/array, file:
"fix ave/chunk"_fix_ave_chunk.html: per-atom vectors: global array, file:
"fix ave/histo"_fix_ave_histo.html: global/per-atom/local scalars and vectors: global array, file:
"fix ave/correlate"_fix_ave_correlate.html: global scalars: global array, file:
"fix store/state"_fix_store_state.html: per-atom vectors: per-atom vector/array :tb(c=3,s=:)

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Polarizable models :h3
In polarizable force fields the charge distributions in molecules and
materials respond to their electrostatic environments. Polarizable
systems can be simulated in LAMMPS using three methods:
the fluctuating charge method, implemented in the "QEQ"_fix_qeq.html
package, :ulb,l
the adiabatic core-shell method, implemented in the
"CORESHELL"_Howto_coreshell.html package, :l
the thermalized Drude dipole method, implemented in the
"USER-DRUDE"_Howto_drude.html package. :l,ule
The fluctuating charge method calculates instantaneous charges on
interacting atoms based on the electronegativity equalization
principle. It is implemented in the "fix qeq"_fix_qeq.html which is
available in several variants. It is a relatively efficient technique
since no additional particles are introduced. This method allows for
charge transfer between molecules or atom groups. However, because the
charges are located at the interaction sites, off-plane components of
polarization cannot be represented in planar molecules or atom groups.
The two other methods share the same basic idea: polarizable atoms are
split into one core atom and one satellite particle (called shell or
Drude particle) attached to it by a harmonic spring. Both atoms bear
a charge and they represent collectively an induced electric dipole.
These techniques are computationally more expensive than the QEq
method because of additional particles and bonds. These two
charge-on-spring methods differ in certain features, with the
core-shell model being normally used for ionic/crystalline materials,
whereas the so-called Drude model is normally used for molecular
systems and fluid states.
The core-shell model is applicable to crystalline materials where the
high symmetry around each site leads to stable trajectories of the
core-shell pairs. However, bonded atoms in molecules can be so close
that a core would interact too strongly or even capture the Drude
particle of a neighbor. The Drude dipole model is relatively more
complex in order to remedy this and other issues. Specifically, the
Drude model includes specific thermostatting of the core-Drude pairs
and short-range damping of the induced dipoles.
The three polarization methods can be implemented through a
self-consistent calculation of charges or induced dipoles at each
timestep. In the fluctuating charge scheme this is done by the matrix
inversion method in "fix qeq/point"_fix_qeq.html, but for core-shell
or Drude-dipoles the relaxed-dipoles technique would require an slow
iterative procedure. These self-consistent solutions yield accurate
trajectories since the additional degrees of freedom representing
polarization are massless. An alternative is to attribute a mass to
the additional degrees of freedom and perform time integration using
an extended Lagrangian technique. For the fluctuating charge scheme
this is done by "fix qeq/dynamic"_fix_qeq.html, and for the
charge-on-spring models by the methods outlined in the next two
sections. The assignment of masses to the additional degrees of
freedom can lead to unphysical trajectories if care is not exerted in
choosing the parameters of the polarizable models and the simulation
conditions.
In the core-shell model the vibration of the shells is kept faster
than the ionic vibrations to mimic the fast response of the
polarizable electrons. But in molecular systems thermalizing the
core-Drude pairs at temperatures comparable to the rest of the
simulation leads to several problems (kinetic energy transfer, too
short a timestep, etc.) In order to avoid these problems the relative
motion of the Drude particles with respect to their cores is kept
"cold" so the vibration of the core-Drude pairs is very slow,
approaching the self-consistent regime. In both models the
temperature is regulated using the velocities of the center of mass of
core+shell (or Drude) pairs, but in the Drude model the actual
relative core-Drude particle motion is thermostatted separately as
well.

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Multi-replica simulations :h3
Several commands in LAMMPS run multi-replica simulations, meaning
that multiple instances (replicas) of your simulation are run
simultaneously, with small amounts of data exchanged between replicas
periodically.
These are the relevant commands:
"neb"_neb.html for nudged elastic band calculations
"neb_spin"_neb_spin.html for magnetic nudged elastic band calculations
"prd"_prd.html for parallel replica dynamics
"tad"_tad.html for temperature accelerated dynamics
"temper"_temper.html for parallel tempering
"fix pimd"_fix_pimd.html for path-integral molecular dynamics (PIMD) :ul
NEB is a method for finding transition states and barrier energies.
PRD and TAD are methods for performing accelerated dynamics to find
and perform infrequent events. Parallel tempering or replica exchange
runs different replicas at a series of temperature to facilitate
rare-event sampling.
These commands can only be used if LAMMPS was built with the REPLICA
package. See the "Build package"_Build_package.html doc page for more
info.
PIMD runs different replicas whose individual particles are coupled
together by springs to model a system or ring-polymers.
This commands can only be used if LAMMPS was built with the USER-MISC
package. See the "Build package"_Build_package.html doc page for more
info.
In all these cases, you must run with one or more processors per
replica. The processors assigned to each replica are determined at
run-time by using the "-partition command-line
switch"_Run_options.html to launch LAMMPS on multiple partitions,
which in this context are the same as replicas. E.g. these commands:
mpirun -np 16 lmp_linux -partition 8x2 -in in.temper
mpirun -np 8 lmp_linux -partition 8x1 -in in.neb :pre
would each run 8 replicas, on either 16 or 8 processors. Note the use
of the "-in command-line switch"_Run_options.html to specify the input
script which is required when running in multi-replica mode.
Also note that with MPI installed on a machine (e.g. your desktop),
you can run on more (virtual) processors than you have physical
processors. Thus the above commands could be run on a
single-processor (or few-processor) desktop so that you can run
a multi-replica simulation on more replicas than you have
physical processors.

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Restart a simulation :h3
There are 3 ways to continue a long LAMMPS simulation. Multiple
"run"_run.html commands can be used in the same input script. Each
run will continue from where the previous run left off. Or binary
restart files can be saved to disk using the "restart"_restart.html
command. At a later time, these binary files can be read via a
"read_restart"_read_restart.html command in a new script. Or they can
be converted to text data files using the "-r command-line
switch"_Run_options.html and read by a "read_data"_read_data.html
command in a new script.
Here we give examples of 2 scripts that read either a binary restart
file or a converted data file and then issue a new run command to
continue where the previous run left off. They illustrate what
settings must be made in the new script. Details are discussed in the
documentation for the "read_restart"_read_restart.html and
"read_data"_read_data.html commands.
Look at the {in.chain} input script provided in the {bench} directory
of the LAMMPS distribution to see the original script that these 2
scripts are based on. If that script had the line
restart 50 tmp.restart :pre
added to it, it would produce 2 binary restart files (tmp.restart.50
and tmp.restart.100) as it ran.
This script could be used to read the 1st restart file and re-run the
last 50 timesteps:
read_restart tmp.restart.50 :pre
neighbor 0.4 bin
neigh_modify every 1 delay 1 :pre
fix 1 all nve
fix 2 all langevin 1.0 1.0 10.0 904297 :pre
timestep 0.012 :pre
run 50 :pre
Note that the following commands do not need to be repeated because
their settings are included in the restart file: {units, atom_style,
special_bonds, pair_style, bond_style}. However these commands do
need to be used, since their settings are not in the restart file:
{neighbor, fix, timestep}.
If you actually use this script to perform a restarted run, you will
notice that the thermodynamic data match at step 50 (if you also put a
"thermo 50" command in the original script), but do not match at step
100. This is because the "fix langevin"_fix_langevin.html command
uses random numbers in a way that does not allow for perfect restarts.
As an alternate approach, the restart file could be converted to a data
file as follows:
lmp_g++ -r tmp.restart.50 tmp.restart.data :pre
Then, this script could be used to re-run the last 50 steps:
units lj
atom_style bond
pair_style lj/cut 1.12
pair_modify shift yes
bond_style fene
special_bonds 0.0 1.0 1.0 :pre
read_data tmp.restart.data :pre
neighbor 0.4 bin
neigh_modify every 1 delay 1 :pre
fix 1 all nve
fix 2 all langevin 1.0 1.0 10.0 904297 :pre
timestep 0.012 :pre
reset_timestep 50
run 50 :pre
Note that nearly all the settings specified in the original {in.chain}
script must be repeated, except the {pair_coeff} and {bond_coeff}
commands since the new data file lists the force field coefficients.
Also, the "reset_timestep"_reset_timestep.html command is used to tell
LAMMPS the current timestep. This value is stored in restart files,
but not in data files.

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
SPC water model :h3
The SPC water model specifies a 3-site rigid water molecule with
charges and Lennard-Jones parameters assigned to each of the 3 atoms.
In LAMMPS the "fix shake"_fix_shake.html command can be used to hold
the two O-H bonds and the H-O-H angle rigid. A bond style of
{harmonic} and an angle style of {harmonic} or {charmm} should also be
used.
These are the additional parameters (in real units) to set for O and H
atoms and the water molecule to run a rigid SPC model.
O mass = 15.9994
H mass = 1.008
O charge = -0.820
H charge = 0.410
LJ epsilon of OO = 0.1553
LJ sigma of OO = 3.166
LJ epsilon, sigma of OH, HH = 0.0
r0 of OH bond = 1.0
theta of HOH angle = 109.47 :all(b),p
Note that as originally proposed, the SPC model was run with a 9
Angstrom cutoff for both LJ and Coulombic terms. It can also be used
with long-range Coulombics (Ewald or PPPM in LAMMPS), without changing
any of the parameters above, though it becomes a different model in
that mode of usage.
The SPC/E (extended) water model is the same, except
the partial charge assignments change:
O charge = -0.8476
H charge = 0.4238 :all(b),p
See the "(Berendsen)"_#howto-Berendsen reference for more details on both
the SPC and SPC/E models.
Wikipedia also has a nice article on "water
models"_http://en.wikipedia.org/wiki/Water_model.
:line
:link(howto-Berendsen)
[(Berendsen)] Berendsen, Grigera, Straatsma, J Phys Chem, 91,
6269-6271 (1987).

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Finite-size spherical and aspherical particles :h3
Typical MD models treat atoms or particles as point masses. Sometimes
it is desirable to have a model with finite-size particles such as
spheroids or ellipsoids or generalized aspherical bodies. The
difference is that such particles have a moment of inertia, rotational
energy, and angular momentum. Rotation is induced by torque coming
from interactions with other particles.
LAMMPS has several options for running simulations with these kinds of
particles. The following aspects are discussed in turn:
atom styles
pair potentials
time integration
computes, thermodynamics, and dump output
rigid bodies composed of finite-size particles :ul
Example input scripts for these kinds of models are in the body,
colloid, dipole, ellipse, line, peri, pour, and tri directories of the
"examples directory"_Examples.html in the LAMMPS distribution.
Atom styles :h4
There are several "atom styles"_atom_style.html that allow for
definition of finite-size particles: sphere, dipole, ellipsoid, line,
tri, peri, and body.
The sphere style defines particles that are spheroids and each
particle can have a unique diameter and mass (or density). These
particles store an angular velocity (omega) and can be acted upon by
torque. The "set" command can be used to modify the diameter and mass
of individual particles, after then are created.
The dipole style does not actually define finite-size particles, but
is often used in conjunction with spherical particles, via a command
like
atom_style hybrid sphere dipole :pre
This is because when dipoles interact with each other, they induce
torques, and a particle must be finite-size (i.e. have a moment of
inertia) in order to respond and rotate. See the "atom_style
dipole"_atom_style.html command for details. The "set" command can be
used to modify the orientation and length of the dipole moment of
individual particles, after then are created.
The ellipsoid style defines particles that are ellipsoids and thus can
be aspherical. Each particle has a shape, specified by 3 diameters,
and mass (or density). These particles store an angular momentum and
their orientation (quaternion), and can be acted upon by torque. They
do not store an angular velocity (omega), which can be in a different
direction than angular momentum, rather they compute it as needed.
The "set" command can be used to modify the diameter, orientation, and
mass of individual particles, after then are created. It also has a
brief explanation of what quaternions are.
The line style defines line segment particles with two end points and
a mass (or density). They can be used in 2d simulations, and they can
be joined together to form rigid bodies which represent arbitrary
polygons.
The tri style defines triangular particles with three corner points
and a mass (or density). They can be used in 3d simulations, and they
can be joined together to form rigid bodies which represent arbitrary
particles with a triangulated surface.
The peri style is used with "Peridynamic models"_pair_peri.html and
defines particles as having a volume, that is used internally in the
"pair_style peri"_pair_peri.html potentials.
The body style allows for definition of particles which can represent
complex entities, such as surface meshes of discrete points,
collections of sub-particles, deformable objects, etc. The body style
is discussed in more detail on the "Howto body"_Howto_body.html doc
page.
Note that if one of these atom styles is used (or multiple styles via
the "atom_style hybrid"_atom_style.html command), not all particles in
the system are required to be finite-size or aspherical.
For example, in the ellipsoid style, if the 3 shape parameters are set
to the same value, the particle will be a sphere rather than an
ellipsoid. If the 3 shape parameters are all set to 0.0 or if the
diameter is set to 0.0, it will be a point particle. In the line or
tri style, if the lineflag or triflag is specified as 0, then it
will be a point particle.
Some of the pair styles used to compute pairwise interactions between
finite-size particles also compute the correct interaction with point
particles as well, e.g. the interaction between a point particle and a
finite-size particle or between two point particles. If necessary,
"pair_style hybrid"_pair_hybrid.html can be used to insure the correct
interactions are computed for the appropriate style of interactions.
Likewise, using groups to partition particles (ellipsoids versus
spheres versus point particles) will allow you to use the appropriate
time integrators and temperature computations for each class of
particles. See the doc pages for various commands for details.
Also note that for "2d simulations"_dimension.html, atom styles sphere
and ellipsoid still use 3d particles, rather than as circular disks or
ellipses. This means they have the same moment of inertia as the 3d
object. When temperature is computed, the correct degrees of freedom
are used for rotation in a 2d versus 3d system.
Pair potentials :h4
When a system with finite-size particles is defined, the particles
will only rotate and experience torque if the force field computes
such interactions. These are the various "pair
styles"_pair_style.html that generate torque:
"pair_style gran/history"_pair_gran.html
"pair_style gran/hertzian"_pair_gran.html
"pair_style gran/no_history"_pair_gran.html
"pair_style dipole/cut"_pair_dipole.html
"pair_style gayberne"_pair_gayberne.html
"pair_style resquared"_pair_resquared.html
"pair_style brownian"_pair_brownian.html
"pair_style lubricate"_pair_lubricate.html
"pair_style line/lj"_pair_line_lj.html
"pair_style tri/lj"_pair_tri_lj.html
"pair_style body/nparticle"_pair_body_nparticle.html :ul
The granular pair styles are used with spherical particles. The
dipole pair style is used with the dipole atom style, which could be
applied to spherical or ellipsoidal particles. The GayBerne and
REsquared potentials require ellipsoidal particles, though they will
also work if the 3 shape parameters are the same (a sphere). The
Brownian and lubrication potentials are used with spherical particles.
The line, tri, and body potentials are used with line segment,
triangular, and body particles respectively.
Time integration :h4
There are several fixes that perform time integration on finite-size
spherical particles, meaning the integrators update the rotational
orientation and angular velocity or angular momentum of the particles:
"fix nve/sphere"_fix_nve_sphere.html
"fix nvt/sphere"_fix_nvt_sphere.html
"fix npt/sphere"_fix_npt_sphere.html :ul
Likewise, there are 3 fixes that perform time integration on
ellipsoidal particles:
"fix nve/asphere"_fix_nve_asphere.html
"fix nvt/asphere"_fix_nvt_asphere.html
"fix npt/asphere"_fix_npt_asphere.html :ul
The advantage of these fixes is that those which thermostat the
particles include the rotational degrees of freedom in the temperature
calculation and thermostatting. The "fix langevin"_fix_langevin.html
command can also be used with its {omgea} or {angmom} options to
thermostat the rotational degrees of freedom for spherical or
ellipsoidal particles. Other thermostatting fixes only operate on the
translational kinetic energy of finite-size particles.
These fixes perform constant NVE time integration on line segment,
triangular, and body particles:
"fix nve/line"_fix_nve_line.html
"fix nve/tri"_fix_nve_tri.html
"fix nve/body"_fix_nve_body.html :ul
Note that for mixtures of point and finite-size particles, these
integration fixes can only be used with "groups"_group.html which
contain finite-size particles.
Computes, thermodynamics, and dump output :h4
There are several computes that calculate the temperature or
rotational energy of spherical or ellipsoidal particles:
"compute temp/sphere"_compute_temp_sphere.html
"compute temp/asphere"_compute_temp_asphere.html
"compute erotate/sphere"_compute_erotate_sphere.html
"compute erotate/asphere"_compute_erotate_asphere.html :ul
These include rotational degrees of freedom in their computation. If
you wish the thermodynamic output of temperature or pressure to use
one of these computes (e.g. for a system entirely composed of
finite-size particles), then the compute can be defined and the
"thermo_modify"_thermo_modify.html command used. Note that by default
thermodynamic quantities will be calculated with a temperature that
only includes translational degrees of freedom. See the
"thermo_style"_thermo_style.html command for details.
These commands can be used to output various attributes of finite-size
particles:
"dump custom"_dump.html
"compute property/atom"_compute_property_atom.html
"dump local"_dump.html
"compute body/local"_compute_body_local.html :ul
Attributes include the dipole moment, the angular velocity, the
angular momentum, the quaternion, the torque, the end-point and
corner-point coordinates (for line and tri particles), and
sub-particle attributes of body particles.
Rigid bodies composed of finite-size particles :h4
The "fix rigid"_fix_rigid.html command treats a collection of
particles as a rigid body, computes its inertia tensor, sums the total
force and torque on the rigid body each timestep due to forces on its
constituent particles, and integrates the motion of the rigid body.
If any of the constituent particles of a rigid body are finite-size
particles (spheres or ellipsoids or line segments or triangles), then
their contribution to the inertia tensor of the body is different than
if they were point particles. This means the rotational dynamics of
the rigid body will be different. Thus a model of a dimer is
different if the dimer consists of two point masses versus two
spheroids, even if the two particles have the same mass. Finite-size
particles that experience torque due to their interaction with other
particles will also impart that torque to a rigid body they are part
of.
See the "fix rigid" command for example of complex rigid-body models
it is possible to define in LAMMPS.
Note that the "fix shake"_fix_shake.html command can also be used to
treat 2, 3, or 4 particles as a rigid body, but it always assumes the
particles are point masses.
Also note that body particles cannot be modeled with the "fix
rigid"_fix_rigid.html command. Body particles are treated by LAMMPS
as single particles, though they can store internal state, such as a
list of sub-particles. Individual body particles are typically treated
as rigid bodies, and their motion integrated with a command like "fix
nve/body"_fix_nve_body.html. Interactions between pairs of body
particles are computed via a command like "pair_style
body/nparticle"_pair_body_nparticle.html.

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Magnetic spins :h3
The magnetic spin simulations are enabled by the SPIN package, whose
implementation is detailed in "Tranchida"_#Tranchida.
The model represents the simulation of atomic magnetic spins coupled
to lattice vibrations. The dynamics of those magnetic spins can be used
to simulate a broad range a phenomena related to magneto-elasticity, or
or to study the influence of defects on the magnetic properties of
materials.
The magnetic spins are interacting with each others and with the
lattice via pair interactions. Typically, the magnetic exchange
interaction can be defined using the
"pair/spin/exchange"_pair_spin_exchange.html command. This exchange
applies a magnetic torque to a given spin, considering the orientation
of its neighboring spins and their relative distances.
It also applies a force on the atoms as a function of the spin
orientations and their associated inter-atomic distances.
The command "fix precession/spin"_fix_precession_spin.html allows to
apply a constant magnetic torque on all the spins in the system. This
torque can be an external magnetic field (Zeeman interaction), or an
uniaxial magnetic anisotropy.
A Langevin thermostat can be applied to those magnetic spins using
"fix langevin/spin"_fix_langevin_spin.html. Typically, this thermostat
can be coupled to another Langevin thermostat applied to the atoms
using "fix langevin"_fix_langevin.html in order to simulate
thermostatted spin-lattice systems.
The magnetic Gilbert damping can also be applied using "fix
langevin/spin"_fix_langevin_spin.html. It allows to either dissipate
the thermal energy of the Langevin thermostat, or to perform a
relaxation of the magnetic configuration toward an equilibrium state.
The command "fix setforce/spin"_fix_setforce.html allows to set the
components of the magnetic precession vectors (while erasing and
replacing the previously computed magnetic precession vectors on
the atom).
This command can be used to freeze the magnetic moment of certain
atoms in the simulation by zeroing their precession vector.
The command "fix nve/spin"_fix_nve_spin.html can be used to
perform a symplectic integration of the combined dynamics of spins
and atomic motions.
The minimization style "min/spin"_min_spin.html can be applied
to the spins to perform a minimization of the spin configuration.
All the computed magnetic properties can be output by two main
commands. The first one is "compute spin"_compute_spin.html, that
enables to evaluate magnetic averaged quantities, such as the total
magnetization of the system along x, y, or z, the spin temperature, or
the magnetic energy. The second command is "compute
property/atom"_compute_property_atom.html. It enables to output all the
per atom magnetic quantities. Typically, the orientation of a given
magnetic spin, or the magnetic force acting on this spin.
:line
:link(Tranchida)
[(Tranchida)] Tranchida, Plimpton, Thibaudeau and Thompson,
Journal of Computational Physics, 372, 406-425, (2018).

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Calculate temperature :h3
Temperature is computed as kinetic energy divided by some number of
degrees of freedom (and the Boltzmann constant). Since kinetic energy
is a function of particle velocity, there is often a need to
distinguish between a particle's advection velocity (due to some
aggregate motion of particles) and its thermal velocity. The sum of
the two is the particle's total velocity, but the latter is often what
is wanted to compute a temperature.
LAMMPS has several options for computing temperatures, any of which
can be used in "thermostatting"_Howto_thermostat.html and
"barostatting"_Howto_barostat.html. These "compute
commands"_compute.html calculate temperature:
"compute temp"_compute_temp.html
"compute temp/sphere"_compute_temp_sphere.html
"compute temp/asphere"_compute_temp_asphere.html
"compute temp/com"_compute_temp_com.html
"compute temp/deform"_compute_temp_deform.html
"compute temp/partial"_compute_temp_partial.html
"compute temp/profile"_compute_temp_profile.html
"compute temp/ramp"_compute_temp_ramp.html
"compute temp/region"_compute_temp_region.html :ul
All but the first 3 calculate velocity biases directly (e.g. advection
velocities) that are removed when computing the thermal temperature.
"Compute temp/sphere"_compute_temp_sphere.html and "compute
temp/asphere"_compute_temp_asphere.html compute kinetic energy for
finite-size particles that includes rotational degrees of freedom.
They both allow for velocity biases indirectly, via an optional extra
argument which is another temperature compute that subtracts a
velocity bias. This allows the translational velocity of spherical or
aspherical particles to be adjusted in prescribed ways.

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Thermostats :h3
Thermostatting means controlling the temperature of particles in an MD
simulation. "Barostatting"_Howto_barostat.html means controlling the
pressure. Since the pressure includes a kinetic component due to
particle velocities, both these operations require calculation of the
temperature. Typically a target temperature (T) and/or pressure (P)
is specified by the user, and the thermostat or barostat attempts to
equilibrate the system to the requested T and/or P.
Thermostatting in LAMMPS is performed by "fixes"_fix.html, or in one
case by a pair style. Several thermostatting fixes are available:
Nose-Hoover (nvt), Berendsen, CSVR, Langevin, and direct rescaling
(temp/rescale). Dissipative particle dynamics (DPD) thermostatting
can be invoked via the {dpd/tstat} pair style:
"fix nvt"_fix_nh.html
"fix nvt/sphere"_fix_nvt_sphere.html
"fix nvt/asphere"_fix_nvt_asphere.html
"fix nvt/sllod"_fix_nvt_sllod.html
"fix temp/berendsen"_fix_temp_berendsen.html
"fix temp/csvr"_fix_temp_csvr.html
"fix langevin"_fix_langevin.html
"fix temp/rescale"_fix_temp_rescale.html
"pair_style dpd/tstat"_pair_dpd.html :ul
"Fix nvt"_fix_nh.html only thermostats the translational velocity of
particles. "Fix nvt/sllod"_fix_nvt_sllod.html also does this, except
that it subtracts out a velocity bias due to a deforming box and
integrates the SLLOD equations of motion. See the "Howto
nemd"_Howto_nemd.html doc page for further details. "Fix
nvt/sphere"_fix_nvt_sphere.html and "fix
nvt/asphere"_fix_nvt_asphere.html thermostat not only translation
velocities but also rotational velocities for spherical and aspherical
particles.
NOTE: A recent (2017) book by "(Daivis and Todd)"_#Daivis-thermostat
discusses use of the SLLOD method and non-equilibrium MD (NEMD)
thermostatting generally, for both simple and complex fluids,
e.g. molecular systems. The latter can be tricky to do correctly.
DPD thermostatting alters pairwise interactions in a manner analogous
to the per-particle thermostatting of "fix
langevin"_fix_langevin.html.
Any of the thermostatting fixes can use "temperature
computes"_Howto_thermostat.html that remove bias which has two
effects. First, the current calculated temperature, which is compared
to the requested target temperature, is calculated with the velocity
bias removed. Second, the thermostat adjusts only the thermal
temperature component of the particle's velocities, which are the
velocities with the bias removed. The removed bias is then added back
to the adjusted velocities. See the doc pages for the individual
fixes and for the "fix_modify"_fix_modify.html command for
instructions on how to assign a temperature compute to a
thermostatting fix. For example, you can apply a thermostat to only
the x and z components of velocity by using it in conjunction with
"compute temp/partial"_compute_temp_partial.html. Of you could
thermostat only the thermal temperature of a streaming flow of
particles without affecting the streaming velocity, by using "compute
temp/profile"_compute_temp_profile.html.
NOTE: Only the nvt fixes perform time integration, meaning they update
the velocities and positions of particles due to forces and velocities
respectively. The other thermostat fixes only adjust velocities; they
do NOT perform time integration updates. Thus they should be used in
conjunction with a constant NVE integration fix such as these:
"fix nve"_fix_nve.html
"fix nve/sphere"_fix_nve_sphere.html
"fix nve/asphere"_fix_nve_asphere.html :ul
Thermodynamic output, which can be setup via the
"thermo_style"_thermo_style.html command, often includes temperature
values. As explained on the doc page for the
"thermo_style"_thermo_style.html command, the default temperature is
setup by the thermo command itself. It is NOT the temperature
associated with any thermostatting fix you have defined or with any
compute you have defined that calculates a temperature. The doc pages
for the thermostatting fixes explain the ID of the temperature compute
they create. Thus if you want to view these temperatures, you need to
specify them explicitly via the "thermo_style
custom"_thermo_style.html command. Or you can use the
"thermo_modify"_thermo_modify.html command to re-define what
temperature compute is used for default thermodynamic output.
:line
:link(Daivis-thermostat)
[(Daivis and Todd)] Daivis and Todd, Nonequilibrium Molecular Dynamics (book),
Cambridge University Press, https://doi.org/10.1017/9781139017848, (2017).

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
TIP3P water model :h3
The TIP3P water model as implemented in CHARMM
"(MacKerell)"_#howto-tip3p specifies a 3-site rigid water molecule with
charges and Lennard-Jones parameters assigned to each of the 3 atoms.
In LAMMPS the "fix shake"_fix_shake.html command can be used to hold
the two O-H bonds and the H-O-H angle rigid. A bond style of
{harmonic} and an angle style of {harmonic} or {charmm} should also be
used.
These are the additional parameters (in real units) to set for O and H
atoms and the water molecule to run a rigid TIP3P-CHARMM model with a
cutoff. The K values can be used if a flexible TIP3P model (without
fix shake) is desired. If the LJ epsilon and sigma for HH and OH are
set to 0.0, it corresponds to the original 1983 TIP3P model
"(Jorgensen)"_#Jorgensen1.
O mass = 15.9994
H mass = 1.008
O charge = -0.834
H charge = 0.417
LJ epsilon of OO = 0.1521
LJ sigma of OO = 3.1507
LJ epsilon of HH = 0.0460
LJ sigma of HH = 0.4000
LJ epsilon of OH = 0.0836
LJ sigma of OH = 1.7753
K of OH bond = 450
r0 of OH bond = 0.9572
K of HOH angle = 55
theta of HOH angle = 104.52 :all(b),p
These are the parameters to use for TIP3P with a long-range Coulombic
solver (e.g. Ewald or PPPM in LAMMPS), see "(Price)"_#Price1 for
details:
O mass = 15.9994
H mass = 1.008
O charge = -0.830
H charge = 0.415
LJ epsilon of OO = 0.102
LJ sigma of OO = 3.188
LJ epsilon, sigma of OH, HH = 0.0
K of OH bond = 450
r0 of OH bond = 0.9572
K of HOH angle = 55
theta of HOH angle = 104.52 :all(b),p
Wikipedia also has a nice article on "water
models"_http://en.wikipedia.org/wiki/Water_model.
:line
:link(howto-tip3p)
[(MacKerell)] MacKerell, Bashford, Bellott, Dunbrack, Evanseck, Field,
Fischer, Gao, Guo, Ha, et al, J Phys Chem, 102, 3586 (1998).
:link(Jorgensen1)
[(Jorgensen)] Jorgensen, Chandrasekhar, Madura, Impey, Klein, J Chem
Phys, 79, 926 (1983).
:link(Price1)
[(Price)] Price and Brooks, J Chem Phys, 121, 10096 (2004).

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
TIP4P water model :h3
The four-point TIP4P rigid water model extends the traditional
three-point TIP3P model by adding an additional site, usually
massless, where the charge associated with the oxygen atom is placed.
This site M is located at a fixed distance away from the oxygen along
the bisector of the HOH bond angle. A bond style of {harmonic} and an
angle style of {harmonic} or {charmm} should also be used.
A TIP4P model is run with LAMMPS using either this command
for a cutoff model:
"pair_style lj/cut/tip4p/cut"_pair_lj.html
or these two commands for a long-range model:
"pair_style lj/cut/tip4p/long"_pair_lj.html
"kspace_style pppm/tip4p"_kspace_style.html :ul
For both models, the bond lengths and bond angles should be held fixed
using the "fix shake"_fix_shake.html command.
These are the additional parameters (in real units) to set for O and H
atoms and the water molecule to run a rigid TIP4P model with a cutoff
"(Jorgensen)"_#Jorgensen5. Note that the OM distance is specified in
the "pair_style"_pair_style.html command, not as part of the pair
coefficients.
O mass = 15.9994
H mass = 1.008
O charge = -1.040
H charge = 0.520
r0 of OH bond = 0.9572
theta of HOH angle = 104.52
OM distance = 0.15
LJ epsilon of O-O = 0.1550
LJ sigma of O-O = 3.1536
LJ epsilon, sigma of OH, HH = 0.0
Coulombic cutoff = 8.5 :all(b),p
For the TIP4/Ice model (J Chem Phys, 122, 234511 (2005);
http://dx.doi.org/10.1063/1.1931662) these values can be used:
O mass = 15.9994
H mass = 1.008
O charge = -1.1794
H charge = 0.5897
r0 of OH bond = 0.9572
theta of HOH angle = 104.52
OM distance = 0.1577
LJ epsilon of O-O = 0.21084
LJ sigma of O-O = 3.1668
LJ epsilon, sigma of OH, HH = 0.0
Coulombic cutoff = 8.5 :all(b),p
For the TIP4P/2005 model (J Chem Phys, 123, 234505 (2005);
http://dx.doi.org/10.1063/1.2121687), these values can be used:
O mass = 15.9994
H mass = 1.008
O charge = -1.1128
H charge = 0.5564
r0 of OH bond = 0.9572
theta of HOH angle = 104.52
OM distance = 0.1546
LJ epsilon of O-O = 0.1852
LJ sigma of O-O = 3.1589
LJ epsilon, sigma of OH, HH = 0.0
Coulombic cutoff = 8.5 :all(b),p
These are the parameters to use for TIP4P with a long-range Coulombic
solver (e.g. Ewald or PPPM in LAMMPS):
O mass = 15.9994
H mass = 1.008
O charge = -1.0484
H charge = 0.5242
r0 of OH bond = 0.9572
theta of HOH angle = 104.52
OM distance = 0.1250
LJ epsilon of O-O = 0.16275
LJ sigma of O-O = 3.16435
LJ epsilon, sigma of OH, HH = 0.0 :all(b),p
Note that the when using the TIP4P pair style, the neighbor list
cutoff for Coulomb interactions is effectively extended by a distance
2 * (OM distance), to account for the offset distance of the
fictitious charges on O atoms in water molecules. Thus it is
typically best in an efficiency sense to use a LJ cutoff >= Coulomb
cutoff + 2*(OM distance), to shrink the size of the neighbor list.
This leads to slightly larger cost for the long-range calculation, so
you can test the trade-off for your model. The OM distance and the LJ
and Coulombic cutoffs are set in the "pair_style
lj/cut/tip4p/long"_pair_lj.html command.
Wikipedia also has a nice article on "water
models"_http://en.wikipedia.org/wiki/Water_model.
:line
:link(Jorgensen5)
[(Jorgensen)] Jorgensen, Chandrasekhar, Madura, Impey, Klein, J Chem
Phys, 79, 926 (1983).

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
Triclinic (non-orthogonal) simulation boxes :h3
By default, LAMMPS uses an orthogonal simulation box to encompass the
particles. The "boundary"_boundary.html command sets the boundary
conditions of the box (periodic, non-periodic, etc). The orthogonal
box has its "origin" at (xlo,ylo,zlo) and is defined by 3 edge vectors
starting from the origin given by [a] = (xhi-xlo,0,0); [b] =
(0,yhi-ylo,0); [c] = (0,0,zhi-zlo). The 6 parameters
(xlo,xhi,ylo,yhi,zlo,zhi) are defined at the time the simulation box
is created, e.g. by the "create_box"_create_box.html or
"read_data"_read_data.html or "read_restart"_read_restart.html
commands. Additionally, LAMMPS defines box size parameters lx,ly,lz
where lx = xhi-xlo, and similarly in the y and z dimensions. The 6
parameters, as well as lx,ly,lz, can be output via the "thermo_style
custom"_thermo_style.html command.
LAMMPS also allows simulations to be performed in triclinic
(non-orthogonal) simulation boxes shaped as a parallelepiped with
triclinic symmetry. The parallelepiped has its "origin" at
(xlo,ylo,zlo) and is defined by 3 edge vectors starting from the
origin given by [a] = (xhi-xlo,0,0); [b] = (xy,yhi-ylo,0); [c] =
(xz,yz,zhi-zlo). {xy,xz,yz} can be 0.0 or positive or negative values
and are called "tilt factors" because they are the amount of
displacement applied to faces of an originally orthogonal box to
transform it into the parallelepiped. In LAMMPS the triclinic
simulation box edge vectors [a], [b], and [c] cannot be arbitrary
vectors. As indicated, [a] must lie on the positive x axis. [b] must
lie in the xy plane, with strictly positive y component. [c] may have
any orientation with strictly positive z component. The requirement
that [a], [b], and [c] have strictly positive x, y, and z components,
respectively, ensures that [a], [b], and [c] form a complete
right-handed basis. These restrictions impose no loss of generality,
since it is possible to rotate/invert any set of 3 crystal basis
vectors so that they conform to the restrictions.
For example, assume that the 3 vectors [A],[B],[C] are the edge
vectors of a general parallelepiped, where there is no restriction on
[A],[B],[C] other than they form a complete right-handed basis i.e.
[A] x [B] . [C] > 0. The equivalent LAMMPS [a],[b],[c] are a linear
rotation of [A], [B], and [C] and can be computed as follows:
:c,image(Eqs/transform.jpg)
where A = | [A] | indicates the scalar length of [A]. The hat symbol (^)
indicates the corresponding unit vector. {beta} and {gamma} are angles
between the vectors described below. Note that by construction,
[a], [b], and [c] have strictly positive x, y, and z components, respectively.
If it should happen that
[A], [B], and [C] form a left-handed basis, then the above equations
are not valid for [c]. In this case, it is necessary
to first apply an inversion. This can be achieved
by interchanging two basis vectors or by changing the sign of one of them.
For consistency, the same rotation/inversion applied to the basis vectors
must also be applied to atom positions, velocities,
and any other vector quantities.
This can be conveniently achieved by first converting to
fractional coordinates in the
old basis and then converting to distance coordinates in the new basis.
The transformation is given by the following equation:
:c,image(Eqs/rotate.jpg)
where {V} is the volume of the box, [X] is the original vector quantity and
[x] is the vector in the LAMMPS basis.
There is no requirement that a triclinic box be periodic in any
dimension, though it typically should be in at least the 2nd dimension
of the tilt (y in xy) if you want to enforce a shift in periodic
boundary conditions across that boundary. Some commands that work
with triclinic boxes, e.g. the "fix deform"_fix_deform.html and "fix
npt"_fix_nh.html commands, require periodicity or non-shrink-wrap
boundary conditions in specific dimensions. See the command doc pages
for details.
The 9 parameters (xlo,xhi,ylo,yhi,zlo,zhi,xy,xz,yz) are defined at the
time the simulation box is created. This happens in one of 3 ways.
If the "create_box"_create_box.html command is used with a region of
style {prism}, then a triclinic box is setup. See the
"region"_region.html command for details. If the
"read_data"_read_data.html command is used to define the simulation
box, and the header of the data file contains a line with the "xy xz
yz" keyword, then a triclinic box is setup. See the
"read_data"_read_data.html command for details. Finally, if the
"read_restart"_read_restart.html command reads a restart file which
was written from a simulation using a triclinic box, then a triclinic
box will be setup for the restarted simulation.
Note that you can define a triclinic box with all 3 tilt factors =
0.0, so that it is initially orthogonal. This is necessary if the box
will become non-orthogonal, e.g. due to the "fix npt"_fix_nh.html or
"fix deform"_fix_deform.html commands. Alternatively, you can use the
"change_box"_change_box.html command to convert a simulation box from
orthogonal to triclinic and vice versa.
As with orthogonal boxes, LAMMPS defines triclinic box size parameters
lx,ly,lz where lx = xhi-xlo, and similarly in the y and z dimensions.
The 9 parameters, as well as lx,ly,lz, can be output via the
"thermo_style custom"_thermo_style.html command.
To avoid extremely tilted boxes (which would be computationally
inefficient), LAMMPS normally requires that no tilt factor can skew
the box more than half the distance of the parallel box length, which
is the 1st dimension in the tilt factor (x for xz). This is required
both when the simulation box is created, e.g. via the
"create_box"_create_box.html or "read_data"_read_data.html commands,
as well as when the box shape changes dynamically during a simulation,
e.g. via the "fix deform"_fix_deform.html or "fix npt"_fix_nh.html
commands.
For example, if xlo = 2 and xhi = 12, then the x box length is 10 and
the xy tilt factor must be between -5 and 5. Similarly, both xz and
yz must be between -(xhi-xlo)/2 and +(yhi-ylo)/2. Note that this is
not a limitation, since if the maximum tilt factor is 5 (as in this
example), then configurations with tilt = ..., -15, -5, 5, 15, 25,
... are geometrically all equivalent. If the box tilt exceeds this
limit during a dynamics run (e.g. via the "fix deform"_fix_deform.html
command), then the box is "flipped" to an equivalent shape with a tilt
factor within the bounds, so the run can continue. See the "fix
deform"_fix_deform.html doc page for further details.
One exception to this rule is if the 1st dimension in the tilt
factor (x for xy) is non-periodic. In that case, the limits on the
tilt factor are not enforced, since flipping the box in that dimension
does not change the atom positions due to non-periodicity. In this
mode, if you tilt the system to extreme angles, the simulation will
simply become inefficient, due to the highly skewed simulation box.
The limitation on not creating a simulation box with a tilt factor
skewing the box more than half the distance of the parallel box length
can be overridden via the "box"_box.html command. Setting the {tilt}
keyword to {large} allows any tilt factors to be specified.
Box flips that may occur using the "fix deform"_fix_deform.html or
"fix npt"_fix_nh.html commands can be turned off using the {flip no}
option with either of the commands.
Note that if a simulation box has a large tilt factor, LAMMPS will run
less efficiently, due to the large volume of communication needed to
acquire ghost atoms around a processor's irregular-shaped sub-domain.
For extreme values of tilt, LAMMPS may also lose atoms and generate an
error.
Triclinic crystal structures are often defined using three lattice
constants {a}, {b}, and {c}, and three angles {alpha}, {beta} and
{gamma}. Note that in this nomenclature, the a, b, and c lattice
constants are the scalar lengths of the edge vectors [a], [b], and [c]
defined above. The relationship between these 6 quantities
(a,b,c,alpha,beta,gamma) and the LAMMPS box sizes (lx,ly,lz) =
(xhi-xlo,yhi-ylo,zhi-zlo) and tilt factors (xy,xz,yz) is as follows:
:c,image(Eqs/box.jpg)
The inverse relationship can be written as follows:
:c,image(Eqs/box_inverse.jpg)
The values of {a}, {b}, {c} , {alpha}, {beta} , and {gamma} can be printed
out or accessed by computes using the
"thermo_style custom"_thermo_style.html keywords
{cella}, {cellb}, {cellc}, {cellalpha}, {cellbeta}, {cellgamma},
respectively.
As discussed on the "dump"_dump.html command doc page, when the BOX
BOUNDS for a snapshot is written to a dump file for a triclinic box,
an orthogonal bounding box which encloses the triclinic simulation box
is output, along with the 3 tilt factors (xy, xz, yz) of the triclinic
box, formatted as follows:
ITEM: BOX BOUNDS xy xz yz
xlo_bound xhi_bound xy
ylo_bound yhi_bound xz
zlo_bound zhi_bound yz :pre
This bounding box is convenient for many visualization programs and is
calculated from the 9 triclinic box parameters
(xlo,xhi,ylo,yhi,zlo,zhi,xy,xz,yz) as follows:
xlo_bound = xlo + MIN(0.0,xy,xz,xy+xz)
xhi_bound = xhi + MAX(0.0,xy,xz,xy+xz)
ylo_bound = ylo + MIN(0.0,yz)
yhi_bound = yhi + MAX(0.0,yz)
zlo_bound = zlo
zhi_bound = zhi :pre
These formulas can be inverted if you need to convert the bounding box
back into the triclinic box parameters, e.g. xlo = xlo_bound -
MIN(0.0,xy,xz,xy+xz).
One use of triclinic simulation boxes is to model solid-state crystals
with triclinic symmetry. The "lattice"_lattice.html command can be
used with non-orthogonal basis vectors to define a lattice that will
tile a triclinic simulation box via the
"create_atoms"_create_atoms.html command.
A second use is to run Parrinello-Rahman dynamics via the "fix
npt"_fix_nh.html command, which will adjust the xy, xz, yz tilt
factors to compensate for off-diagonal components of the pressure
tensor. The analog for an "energy minimization"_minimize.html is
the "fix box/relax"_fix_box_relax.html command.
A third use is to shear a bulk solid to study the response of the
material. The "fix deform"_fix_deform.html command can be used for
this purpose. It allows dynamic control of the xy, xz, yz tilt
factors as a simulation runs. This is discussed in the next section
on non-equilibrium MD (NEMD) simulations.

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Calculate viscosity :h3
The shear viscosity eta of a fluid can be measured in at least 5 ways
using various options in LAMMPS. See the examples/VISCOSITY directory
for scripts that implement the 5 methods discussed here for a simple
Lennard-Jones fluid model. Also, see the "Howto
kappa"_Howto_kappa.html doc page for an analogous discussion for
thermal conductivity.
Eta is a measure of the propensity of a fluid to transmit momentum in
a direction perpendicular to the direction of velocity or momentum
flow. Alternatively it is the resistance the fluid has to being
sheared. It is given by
J = -eta grad(Vstream)
where J is the momentum flux in units of momentum per area per time.
and grad(Vstream) is the spatial gradient of the velocity of the fluid
moving in another direction, normal to the area through which the
momentum flows. Viscosity thus has units of pressure-time.
The first method is to perform a non-equilibrium MD (NEMD) simulation
by shearing the simulation box via the "fix deform"_fix_deform.html
command, and using the "fix nvt/sllod"_fix_nvt_sllod.html command to
thermostat the fluid via the SLLOD equations of motion.
Alternatively, as a second method, one or more moving walls can be
used to shear the fluid in between them, again with some kind of
thermostat that modifies only the thermal (non-shearing) components of
velocity to prevent the fluid from heating up.
NOTE: A recent (2017) book by "(Daivis and Todd)"_#Daivis-viscosity
discusses use of the SLLOD method and non-equilibrium MD (NEMD)
thermostatting generally, for both simple and complex fluids,
e.g. molecular systems. The latter can be tricky to do correctly.
In both cases, the velocity profile setup in the fluid by this
procedure can be monitored by the "fix ave/chunk"_fix_ave_chunk.html
command, which determines grad(Vstream) in the equation above.
E.g. the derivative in the y-direction of the Vx component of fluid
motion or grad(Vstream) = dVx/dy. The Pxy off-diagonal component of
the pressure or stress tensor, as calculated by the "compute
pressure"_compute_pressure.html command, can also be monitored, which
is the J term in the equation above. See the "Howto
nemd"_Howto_nemd.html doc page for details on NEMD simulations.
The third method is to perform a reverse non-equilibrium MD simulation
using the "fix viscosity"_fix_viscosity.html command which implements
the rNEMD algorithm of Muller-Plathe. Momentum in one dimension is
swapped between atoms in two different layers of the simulation box in
a different dimension. This induces a velocity gradient which can be
monitored with the "fix ave/chunk"_fix_ave_chunk.html command.
The fix tallies the cumulative momentum transfer that it performs.
See the "fix viscosity"_fix_viscosity.html command for details.
The fourth method is based on the Green-Kubo (GK) formula which
relates the ensemble average of the auto-correlation of the
stress/pressure tensor to eta. This can be done in a fully
equilibrated simulation which is in contrast to the two preceding
non-equilibrium methods, where momentum flows continuously through the
simulation box.
Here is an example input script that calculates the viscosity of
liquid Ar via the GK formalism:
# Sample LAMMPS input script for viscosity of liquid Ar :pre
units real
variable T equal 86.4956
variable V equal vol
variable dt equal 4.0
variable p equal 400 # correlation length
variable s equal 5 # sample interval
variable d equal $p*$s # dump interval :pre
# convert from LAMMPS real units to SI :pre
variable kB equal 1.3806504e-23 # \[J/K\] Boltzmann
variable atm2Pa equal 101325.0
variable A2m equal 1.0e-10
variable fs2s equal 1.0e-15
variable convert equal $\{atm2Pa\}*$\{atm2Pa\}*$\{fs2s\}*$\{A2m\}*$\{A2m\}*$\{A2m\} :pre
# setup problem :pre
dimension 3
boundary p p p
lattice fcc 5.376 orient x 1 0 0 orient y 0 1 0 orient z 0 0 1
region box block 0 4 0 4 0 4
create_box 1 box
create_atoms 1 box
mass 1 39.948
pair_style lj/cut 13.0
pair_coeff * * 0.2381 3.405
timestep $\{dt\}
thermo $d :pre
# equilibration and thermalization :pre
velocity all create $T 102486 mom yes rot yes dist gaussian
fix NVT all nvt temp $T $T 10 drag 0.2
run 8000 :pre
# viscosity calculation, switch to NVE if desired :pre
#unfix NVT
#fix NVE all nve :pre
reset_timestep 0
variable pxy equal pxy
variable pxz equal pxz
variable pyz equal pyz
fix SS all ave/correlate $s $p $d &
v_pxy v_pxz v_pyz type auto file S0St.dat ave running
variable scale equal $\{convert\}/($\{kB\}*$T)*$V*$s*$\{dt\}
variable v11 equal trap(f_SS\[3\])*$\{scale\}
variable v22 equal trap(f_SS\[4\])*$\{scale\}
variable v33 equal trap(f_SS\[5\])*$\{scale\}
thermo_style custom step temp press v_pxy v_pxz v_pyz v_v11 v_v22 v_v33
run 100000
variable v equal (v_v11+v_v22+v_v33)/3.0
variable ndens equal count(all)/vol
print "average viscosity: $v \[Pa.s\] @ $T K, $\{ndens\} /A^3" :pre
The fifth method is related to the above Green-Kubo method,
but uses the Einstein formulation, analogous to the Einstein
mean-square-displacement formulation for self-diffusivity. The
time-integrated momentum fluxes play the role of Cartesian
coordinates, whose mean-square displacement increases linearly
with time at sufficiently long times.
:line
:link(Daivis-viscosity)
[(Daivis and Todd)] Daivis and Todd, Nonequilibrium Molecular Dynamics (book),
Cambridge University Press, https://doi.org/10.1017/9781139017848, (2017).

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Visualize LAMMPS snapshots :h3
LAMMPS itself does not do visualization, but snapshots from LAMMPS
simulations can be visualized (and analyzed) in a variety of ways.
Mention dump image and dump movie.
LAMMPS snapshots are created by the "dump"_dump.html command which can
create files in several formats. The native LAMMPS dump format is a
text file (see "dump atom" or "dump custom") which can be visualized
by several popular visualization tools. The "dump
image"_dump_image.html and "dump movie"_dump_image.html styles can
output internally rendered images and convert a sequence of them to a
movie during the MD run. Several programs included with LAMMPS as
auxiliary tools can convert between LAMMPS format files and other
formats. See the "Tools"_Tools.html doc page for details.
A Python-based toolkit distributed by our group can read native LAMMPS
dump files, including custom dump files with additional columns of
user-specified atom information, and convert them to various formats
or pipe them into visualization software directly. See the "Pizza.py
WWW site"_pizza for details. Specifically, Pizza.py can convert
LAMMPS dump files into PDB, XYZ, "Ensight"_ensight, and VTK formats.
Pizza.py can pipe LAMMPS dump files directly into the Raster3d and
RasMol visualization programs. Pizza.py has tools that do interactive
3d OpenGL visualization and one that creates SVG images of dump file
snapshots.
:link(pizza,http://www.sandia.gov/~sjplimp/pizza.html)
:link(ensight,http://www.ensight.com)
:link(atomeye,http://mt.seas.upenn.edu/Archive/Graphics/A)

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"Higher level section"_Howto.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Walls :h3
Walls in an MD simulation are typically used to bound particle motion,
i.e. to serve as a boundary condition.
Walls in LAMMPS can be of rough (made of particles) or idealized
surfaces. Ideal walls can be smooth, generating forces only in the
normal direction, or frictional, generating forces also in the
tangential direction.
Rough walls, built of particles, can be created in various ways. The
particles themselves can be generated like any other particle, via the
"lattice"_lattice.html and "create_atoms"_create_atoms.html commands,
or read in via the "read_data"_read_data.html command.
Their motion can be constrained by many different commands, so that
they do not move at all, move together as a group at constant velocity
or in response to a net force acting on them, move in a prescribed
fashion (e.g. rotate around a point), etc. Note that if a time
integration fix like "fix nve"_fix_nve.html or "fix nvt"_fix_nh.html
is not used with the group that contains wall particles, their
positions and velocities will not be updated.
"fix aveforce"_fix_aveforce.html - set force on particles to average value, so they move together
"fix setforce"_fix_setforce.html - set force on particles to a value, e.g. 0.0
"fix freeze"_fix_freeze.html - freeze particles for use as granular walls
"fix nve/noforce"_fix_nve_noforce.html - advect particles by their velocity, but without force
"fix move"_fix_move.html - prescribe motion of particles by a linear velocity, oscillation, rotation, variable :ul
The "fix move"_fix_move.html command offers the most generality, since
the motion of individual particles can be specified with
"variable"_variable.html formula which depends on time and/or the
particle position.
For rough walls, it may be useful to turn off pairwise interactions
between wall particles via the "neigh_modify
exclude"_neigh_modify.html command.
Rough walls can also be created by specifying frozen particles that do
not move and do not interact with mobile particles, and then tethering
other particles to the fixed particles, via a "bond"_bond_style.html.
The bonded particles do interact with other mobile particles.
Idealized walls can be specified via several fix commands. "Fix
wall/gran"_fix_wall_gran.html creates frictional walls for use with
granular particles; all the other commands create smooth walls.
"fix wall/reflect"_fix_wall_reflect.html - reflective flat walls
"fix wall/lj93"_fix_wall.html - flat walls, with Lennard-Jones 9/3 potential
"fix wall/lj126"_fix_wall.html - flat walls, with Lennard-Jones 12/6 potential
"fix wall/colloid"_fix_wall.html - flat walls, with "pair_style colloid"_pair_colloid.html potential
"fix wall/harmonic"_fix_wall.html - flat walls, with repulsive harmonic spring potential
"fix wall/morse"_fix_wall.html - flat walls, with Morse potential
"fix wall/region"_fix_wall_region.html - use region surface as wall
"fix wall/gran"_fix_wall_gran.html - flat or curved walls with "pair_style granular"_pair_gran.html potential :ul
The {lj93}, {lj126}, {colloid}, {harmonic}, and {morse} styles all
allow the flat walls to move with a constant velocity, or oscillate in
time. The "fix wall/region"_fix_wall_region.html command offers the
most generality, since the region surface is treated as a wall, and
the geometry of the region can be a simple primitive volume (e.g. a
sphere, or cube, or plane), or a complex volume made from the union
and intersection of primitive volumes. "Regions"_region.html can also
specify a volume "interior" or "exterior" to the specified primitive
shape or {union} or {intersection}. "Regions"_region.html can also be
"dynamic" meaning they move with constant velocity, oscillate, or
rotate.
The only frictional idealized walls currently in LAMMPS are flat or
curved surfaces specified by the "fix wall/gran"_fix_wall_gran.html
command. At some point we plan to allow regoin surfaces to be used as
frictional walls, as well as triangulated surfaces.

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"Higher level section"_Install.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Download source via Git :h3
All LAMMPS development is coordinated through the "LAMMPS GitHub
site". If you clone the LAMMPS repository onto your local machine, it
has several advantages:
You can stay current with changes to LAMMPS with a single git
command. :ulb,l
You can create your own development branches to add code to LAMMPS. :l
You can submit your new features back to GitHub for inclusion in
LAMMPS. :l,ule
You must have "Git"_git installed on your system to communicate with
the public Git server for LAMMPS.
IMPORTANT NOTE: As of Oct 2016, the official home of public LAMMPS
development is on GitHub. The previously advertised LAMMPS git
repositories on git.lammps.org and bitbucket.org are now deprecated,
may not be up-to-date, and may go away at any time.
:link(git,http://git-scm.com)
You can follow LAMMPS development on 3 different Git branches:
[stable] : this branch is updated with every stable release
[unstable] : this branch is updated with every patch release
[master] : this branch continuously follows ongoing development :ul
To access the Git repositories on your box, use the clone command to
create a local copy of the LAMMPS repository with a command like:
git clone -b unstable https://github.com/lammps/lammps.git mylammps :pre
where "mylammps" is the name of the directory you wish to create on
your machine and "unstable" is one of the 3 branches listed above.
(Note that you actually download all 3 branches; you can switch
between them at any time using "git checkout <branch name>".)
Once the command completes, your directory will contain the same files
as if you unpacked a current LAMMPS tarball, with the exception, that
the HTML documentation files are not included. They can be fetched
from the LAMMPS website by typing "make fetch" in the doc directory.
Or they can be generated from the content provided in doc/src by
typing "make html" from the doc directory.
After initial cloning, as bug fixes and new features are added to
LAMMPS, as listed on "this page"_Errors_bugs.html, you can stay
up-to-date by typing the following Git commands from within the
"mylammps" directory:
git checkout unstable # not needed if you always stay in this branch
git checkout stable # use one of the 3 checkout commands
git checkout master
git pull :pre
Doing a "pull" will not change any files you have added to the LAMMPS
directory structure. It will also not change any existing LAMMPS
files you have edited, unless those files have changed in the
repository. In that case, Git will attempt to merge the new
repository file with your version of the file and tell you if there
are any conflicts. See the Git documentation for details.
If you want to access a particular previous release version of LAMMPS,
you can instead "checkout" any version with a published tag. See the
output of "git tag -l" for the list of tags. The Git command to do
this is as follows.
git checkout tagID :pre
Stable versions and what tagID to use for a particular stable version
are discussed on "this page"_Errors_bugs.html. Note that this command
will print some warnings, because in order to get back to the latest
revision and to be able to update with "git pull" again, you first
will need to first type "git checkout unstable" (or check out any
other desired branch).
Once you have updated your local files with a "git pull" (or "git
checkout"), you still need to re-build LAMMPS if any source files have
changed. To do this, you should cd to the src directory and type:
make purge # remove any deprecated src files
make package-update # sync package files with src files
make foo # re-build for your machine (mpi, serial, etc) :pre
just as described on the "Install patch"_Install_patch.html doc page,
after a patch has been installed.
IMPORTANT NOTE: If you wish to edit/change a src file that is from a
package, you should edit the version of the file inside the package
sub-directory with src, then re-install the package. The version in
the src dir is merely a copy and will be wiped out if you type "make
package-update".
IMPORTANT NOTE: The GitHub servers support both the "git://" and
"https://" access protocols for anonymous read-only access. If you
have a correspondingly configured GitHub account, you may also use SSH
with "git@github.com:/lammps/lammps.git".
The LAMMPS GitHub project is managed by Christoph Junghans (LANL,
junghans at lanl.gov), Axel Kohlmeyer (Temple U, akohlmey at
gmail.com) and Richard Berger (Temple U, richard.berger at
temple.edu).

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"Higher level section"_Install.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Download an executable for Linux :h3
Binaries are available for different versions of Linux:
"Pre-built Ubuntu Linux executables"_#ubuntu
"Pre-built Fedora Linux executables"_#fedora
"Pre-built EPEL Linux executables (RHEL, CentOS)"_#epel
"Pre-built OpenSuse Linux executables"_#opensuse
"Gentoo Linux executable"_#gentoo
"Arch Linux build-script"_#arch :all(b)
:line
Pre-built Ubuntu Linux executables :h4,link(ubuntu)
A pre-built LAMMPS executable suitable for running on the latest
Ubuntu Linux versions, can be downloaded as a Debian package. This
allows you to install LAMMPS with a single command, and stay
up-to-date with the current version of LAMMPS by simply updating your
operating system.
To install the appropriate personal-package archive (PPA), do the
following once:
sudo add-apt-repository ppa:gladky-anton/lammps
sudo apt-get update :pre
To install LAMMPS do the following once:
sudo apt-get install lammps-daily :pre
This downloads an executable named "lmp_daily" to your box, which
can then be used in the usual way to run input scripts:
lmp_daily -in in.lj :pre
To update LAMMPS to the most current version, do the following:
sudo apt-get update :pre
which will also update other packages on your system.
To get a copy of the current documentation and examples:
sudo apt-get install lammps-daily-doc :pre
which will download the doc files in
/usr/share/doc/lammps-daily-doc/doc and example problems in
/usr/share/doc/lammps-doc/examples.
Note that you may still wish to download the tarball to get potential
files and auxiliary tools.
To un-install LAMMPS, do the following:
sudo apt-get remove lammps-daily :pre
Note that the lammps-daily executable is built with the following
sequence of make commands, as if you had done the same with the
unpacked tarball files in the src directory:
make yes-all; make no-lib; make openmpi
Thus it builds with FFTW3 and OpenMPI.
Thanks to Anton Gladky (gladky.anton at gmail.com) for setting up this
Ubuntu package capability.
:line
Pre-built Fedora Linux executables :h4,link(fedora)
Pre-built LAMMPS packages for stable releases are available
in the Fedora Linux distribution as of version 28. The packages
can be installed via the dnf package manager. There are 3 basic
varieties (lammps = no MPI, lammps-mpich = MPICH MPI library,
lammps-openmpi = OpenMPI MPI library) and for each support for
linking to the C library interface (lammps-devel, lammps-mpich-devel,
lammps-openmpi-devel), the header for compiling programs using
the C library interface (lammps-headers), and the LAMMPS python
module for Python 3. All packages can be installed at the same
time and the name of the LAMMPS executable is {lmp} and {lmp_openmpi}
or {lmp_mpich} respectively. By default, {lmp} will refer to the
serial executable, unless one of the MPI environment modules is loaded
("module load mpi/mpich-x86_64" or "module load mpi/openmpi-x86_64").
Then the corresponding parallel LAMMPS executable can be used.
The same mechanism applies when loading the LAMMPS python module.
To install LAMMPS with OpenMPI and run an input in.lj with 2 CPUs do:
dnf install lammps-openmpi
module load mpi/openmpi-x86_64
mpirun -np 2 lmp -in in.lj :pre
The "dnf install" command is needed only once. In case of a new LAMMPS
stable release, "dnf update" will automatically update to the newer
version as soon at the RPM files are built and uploaded to the download
mirrors. The "module load" command is needed once per (shell) session
or shell terminal instance, unless it is automatically loaded from the
shell profile.
Please use "lmp -help" to see which compilation options, packages,
and styles are included in the binary.
Thanks to Christoph Junghans (LANL) for making LAMMPS available in Fedora.
:line
Pre-built EPEL Linux executable :h4,link(epel)
Pre-built LAMMPS packages for stable releases are available
in the "Extra Packages for Enterprise Linux (EPEL) repository"_https://fedoraproject.org/wiki/EPEL
for use with Red Hat Enterprise Linux (RHEL) or CentOS version 7.x
and compatible Linux distributions. Names of packages, executable,
and content are the same as described above for Fedora Linux.
But RHEL/CentOS 7.x uses the "yum" package manager instead of "dnf"
in Fedora 28.
Please use "lmp -help" to see which compilation options, packages,
and styles are included in the binary.
Thanks to Christoph Junghans (LANL) for making LAMMPS available in EPEL.
:line
Pre-built OpenSuse Linux executable :h4,link(opensuse)
A pre-built LAMMPS package for stable releases is available
in OpenSuse as of Leap 15.0. You can install the package with:
zypper install lammps :pre
This includes support for OpenMPI. The name of the LAMMPS executable
is {lmp}. Thus to run an input in parallel on 2 CPUs you would do:
mpirun -np 2 lmp -in in.lj :pre
Please use "lmp -help" to see which compilation options, packages,
and styles are included in the binary.
Thanks to Christoph Junghans (LANL) for making LAMMPS available in OpenSuse.
:line
Gentoo Linux executable :h4,link(gentoo)
LAMMPS is part of Gentoo's main package tree and can be installed by
typing:
% emerge --ask lammps :pre
Note that in Gentoo the LAMMPS source is downloaded and the package is
built on the your machine.
Certain LAMMPS packages can be enable via USE flags, type
% equery uses lammps :pre
for details.
Thanks to Nicolas Bock and Christoph Junghans (LANL) for setting up
this Gentoo capability.
:line
Archlinux build-script :h4,link(arch)
LAMMPS is available via Arch's unofficial Arch User repository (AUR).
There are three scripts available, named lammps, lammps-beta and lammps-git.
They respectively package the stable, patch and git releases.
To install, you will need to have the git package installed. You may use
any of the above names in-place of lammps.
$ git clone https://aur.archlinux.org/lammps.git :pre
$ cd lammps :pre
$ makepkg -s :pre
# makepkg -i :pre
To update, you may repeat the above, or change into the cloned directory,
and execute the following, after which, if there are any changes, you may
use makepkg as above.
$ git pull :pre
Alternatively, you may use an AUR helper to install these packages.
Note that the AUR provides build-scripts that download the source and
the build the package on your machine.

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"Higher level section"_Install.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Applying patches :h3
It is easy to stay current with the most recent LAMMPS patch releases
if you use Git or SVN to track LAMMPS development. Instructions for
how to stay current are on the "Install git"_Install_git.html and
"Install svn"_Install_svn.html doc pages.
If you prefer to download a tarball, as described on the "Install
git"_Install_tarball.html doc page, you can stay current by
downloading "patch files" when new patch releases are made. A link to
a patch file is posted on the "bug and feature
page"_http://lammps.sandia.gov/bug.html of the LAMMPS website, along
with a list of changed files and details about what is in the new patch
release. This page explains how to apply the patch file to your local
LAMMPS directory.
NOTE: You should not apply patch files to a local Git or SVN repo of
LAMMPS, only to an unpacked tarball. Use Git and SVN commands to
update repo versions of LAMMPS.
Here are the steps to apply a patch file. Note that if your version
of LAMMPS is several patch releases behind, you need to apply all the
intervening patch files in succession to bring your version of LAMMPS
up to date.
Download the patch file. You may have to shift-click in your browser
to download the file instead of display it. Patch files have names
like patch.12Dec16. :ulb,l
Put the patch file in your top-level LAMMPS directory, where the
LICENSE and README files are. :l
Apply the patch by typing the following command from your top-level
LAMMPS directory, where the redirected file is the name of the patch
file. :l
patch -bp1 < patch.12Dec16 :pre
A list of updated files print out to the screen. The -b switch
creates backup files of your originals (e.g. src/force.cpp.orig), so
you can manually undo the patch if something goes wrong. :l
Type the following from the src directory, to enforce consistency
between the src and package directories. This is OK to do even if you
don't use one or more packages. If you are applying several patches
successively, you only need to type this once at the end. The purge
command removes deprecated src files if any were removed by the patch
from package sub-directories. :l
make purge
make package-update :pre
Re-build LAMMPS via the "make" command. :l,ule
IMPORTANT NOTE: If you wish to edit/change a src file that is from a
package, you should edit the version of the file inside the package
sub-dir of src, then re-install the package. The version in the src
dir is merely a copy and will be wiped out if you type "make
package-update".

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"Higher level section"_Install.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Download source via SVN :h3
IMPORTANT NOTE: As of Oct 2016, SVN support is now implemented via a
git-to-subversion interface service on GitHub and no longer through a
mirror of the internal SVN repository at Sandia.
You must have the "Subversion (SVN) client software"_svn installed on
your system to communicate with the Git server in this mode.
:link(svn,http://subversion.apache.org)
You can follow LAMMPS development on 3 different SVN branches:
[stable] : this branch is updated with every stable release
[unstable] : this branch is updated with every patch release
[master] : this branch continuously follows ongoing development :ul
The corresponding command lines to do an initial checkout are as
follows. (Note that unlike Git, you must perform a separate checkout
into a unique directory for each of the 3 branches.)
svn checkout https://github.com/lammps/lammps.git/branches/unstable mylammps
svn checkout https://github.com/lammps/lammps.git/branches/stable mylammps
svn checkout https://github.com/lammps/lammps.git/trunk mylammps :pre
where "mylammps" is the name of the directory you wish to create on
your machine.
Once the command completes, your directory will contain the same files
as if you unpacked a current LAMMPS tarball, with the exception, that
the HTML documentation files are not included. They can be fetched
from the LAMMPS website by typing "make fetch" in the doc directory.
Or they can be generated from the content provided in doc/src by
typing "make html" from the doc directory.
After initial checkout, as bug fixes and new features are added to
LAMMPS, as listed on "this page"_Errors_bugs.html, you can stay
up-to-date by typing the following SVN commands from within the
"mylammps" directory:
svn update :pre
You can also check if there are any updates by typing:
svn -qu status :pre
Doing an "update" will not change any files you have added to the
LAMMPS directory structure. It will also not change any existing
LAMMPS files you have edited, unless those files have changed in the
repository. In that case, SVN will attempt to merge the new
repository file with your version of the file and tell you if there
are any conflicts. See the SVN documentation for details.
Please refer to the "subversion client support help pages on
GitHub"_https://help.github.com/articles/support-for-subversion-clients
if you want to use advanced features like accessing particular
previous release versions via tags.
Once you have updated your local files with an "svn update" (or "svn
co"), you still need to re-build LAMMPS if any source files have
changed. To do this, you should cd to the src directory and type:
make purge # remove any deprecated src files
make package-update # sync package files with src files
make foo # re-build for your machine (mpi, serial, etc) :pre
just as described on the "Install patch"_Install_patch.html doc page,
after a patch has been installed.
IMPORTANT NOTE: If you wish to edit/change a src file that is from a
package, you should edit the version of the file inside the package
sub-directory with src, then re-install the package. The version in
the src dir is merely a copy and will be wiped out if you type "make
package-update".
The LAMMPS GitHub project is managed by Christoph Junghans (LANL,
junghans at lanl.gov), Axel Kohlmeyer (Temple U, akohlmey at
gmail.com) and Richard Berger (Temple U, richard.berger at
temple.edu).

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"Higher level section"_Install.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Download source and documentation as a tarball :h3
You can download a current LAMMPS tarball from the "download page"_download
of the "LAMMPS website"_lws.
:link(download,http://lammps.sandia.gov/download.html)
:link(bug,http://lammps.sandia.gov/bug.html)
:link(older,http://lammps.sandia.gov/tars)
You have two choices of tarballs, either the most recent stable
release or the most current patch release. Stable releases occur a
few times per year, and undergo more testing before release. Patch
releases occur a couple times per month. The new contents in all
releases are listed on the "bug and feature page"_bug of the website.
Both tarballs include LAMMPS documentation (HTML and PDF files)
corresponding to that version. The download page also has an option
to download the current-version LAMMPS documentation by itself.
Older versions of LAMMPS can also be downloaded from "this
page"_older.
Once you have a tarball, unzip and untar it with the following
command:
tar -xzvf lammps*.tar.gz :pre
This will create a LAMMPS directory with the version date
in its name, e.g. lammps-23Jun18.
:line
You can also download a zip file via the "Clone or download" button on
the "LAMMPS GitHub site"_git. The file name will be lammps-master.zip
which can be unzipped with the following command, to create
a lammps-master dir:
unzip lammps*.zip :pre
This version is the most up-to-date LAMMPS development version. It
will have the date of the most recent patch release (see the file
src/version.h). But it will also include any new bug-fixes or
features added since the last patch release. They will be included in
the next patch release tarball.
:link(git,https://github.com/lammps/lammps)
:line
If you download a current LAMMPS tarball, one way to stay current as
new patch tarballs are released, is to download a patch file which you
can apply to your local directory to update it for each new patch
release. (Or of course you could just download the newest tarball
periodically.)
The patch files are posted on the "bug and feature page"_bug of the
website, along with a list of changed files and details about what is
in the new patch release. Instructions for applying a patch file are
on the "Install patch"_Install_patch.html doc page.

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"Higher level section"_Install.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Download an executable for Windows :h3
Pre-compiled Windows installers which install LAMMPS executables on a
Windows system can be downloaded from this site:
"http://packages.lammps.org/windows.html"_http://packages.lammps.org/windows.html
Note that each installer package has a date in its name, which
corresponds to the LAMMPS version of the same date. Installers for
current and older versions of LAMMPS are available. 32-bit and 64-bit
installers are available, and each installer contains both a serial
and parallel executable. The installer site also explains how to
install the Windows MPI package (MPICH2 from Argonne National Labs),
needed to run in parallel.
The LAMMPS binaries contain all optional packages included in the
source distribution except: KIM, KOKKOS, USER-INTEL, and USER-QMMM.
The serial version also does not include the MPIIO and
USER-LB packages. GPU support is provided for OpenCL.
The installer site also has instructions on how to run LAMMPS under
Windows, once it is installed, in both serial and parallel.
When you download the installer package, you run it on your Windows
machine. It will then prompt you with a dialog, where you can choose
the installation directory, unpack and copy several executables,
potential files, documentation pdfs, selected example files, etc. It
will then update a few system settings (e.g. PATH, LAMMPS_POTENTIALS)
and add an entry into the Start Menu (with references to the
documentation, LAMMPS homepage and more). From that menu, there is
also a link to an uninstaller that removes the files and undoes the
environment manipulations.
Note that to update to a newer version of LAMMPS, you should typically
uninstall the version you currently have, download a new installer,
and go through the install procedure described above. I.e. the same
procedure for installing/updating most Windows programs. You can
install multiple versions of LAMMPS (in different directories), but
only the executable for the last-installed package will be found
automatically, so this should only be done for debugging purposes.
Thanks to Axel Kohlmeyer (Temple U, akohlmey at gmail.com) for setting
up this Windows capability.

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"Previous Section"_Manual.html - "LAMMPS WWW Site"_lws -
"LAMMPS Documentation"_ld - "LAMMPS Commands"_lc - "Next
Section"_Install.html :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands.html#comm)
:line
Introduction :h2
These pages provide a brief introduction to LAMMPS.
<!-- RST
.. toctree::
:maxdepth: 1
Intro_overview
Manual_version
Intro_features
Intro_nonfeatures
Intro_opensource
Intro_authors
Intro_website
END_RST -->
<!-- HTML_ONLY -->
"Overview of LAMMPS"_Intro_overview.html
"LAMMPS features"_Intro_features.html
"LAMMPS non-features"_Intro_nonfeatures.html
"LAMMPS open-source license"_Intro_license.html
"LAMMPS authors"_Intro_authors.html
"Additional website links"_Intro_website.html :all(b)
<!-- END_HTML_ONLY -->

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"Higher level section"_Intro.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Authors of LAMMPS :h3
The primary LAMMPS developers are at Sandia National Labs and Temple
University:
"Steve Plimpton"_sjp, sjplimp at sandia.gov
Aidan Thompson, athomps at sandia.gov
Stan Moore, stamoor at sandia.gov
Axel Kohlmeyer, akohlmey at gmail.com
Richard Berger, richard.berger at temple.edu :ul
:link(sjp,http://www.cs.sandia.gov/~sjplimp)
Past developers include Paul Crozier and Mark Stevens, both at Sandia,
and Ray Shan, now at Materials Design.
:line
The "Authors page"_http://lammps.sandia.gov/authors.html of the
"LAMMPS website"_lws has a comprehensive list of all the individuals
who have contributed code for a new feature or command or tool to
LAMMPS.
:line
The following folks deserve special recognition. Many of the packages
they have written are unique for an MD code and LAMMPS would not be as
general-purpose as it is without their expertise and efforts.
Metin Aktulga (MSU), USER-REAXC package for C version of ReaxFF
Mike Brown (Intel), GPU and USER-INTEL packages
Colin Denniston (U Western Ontario), USER-LB package
Georg Ganzenmuller (EMI), USER-SMD and USER-SPH packages
Andres Jaramillo-Botero (Caltech), USER-EFF package for electron force field
Reese Jones (Sandia) and colleagues, USER-ATC package for atom/continuum coupling
Christoph Kloss (DCS Computing), LIGGGHTS code for granular materials, built on top of LAMMPS
Rudra Mukherjee (JPL), POEMS package for articulated rigid body motion
Trung Ngyuen (Northwestern U), GPU and RIGID and BODY packages
Mike Parks (Sandia), PERI package for Peridynamics
Roy Pollock (LLNL), Ewald and PPPM solvers
Christian Trott (Sandia), USER-CUDA and KOKKOS packages
Ilya Valuev (JIHT), USER-AWPMD package for wave packet MD
Greg Wagner (Northwestern U), MEAM package for MEAM potential :ul
:line
As discussed on the "History
page"_http://lammps.sandia.gov/history.html of the website, LAMMPS
originated as a cooperative project between DOE labs and industrial
partners. Folks involved in the design and testing of the original
version of LAMMPS were the following:
John Carpenter (Mayo Clinic, formerly at Cray Research)
Terry Stouch (Lexicon Pharmaceuticals, formerly at Bristol Myers Squibb)
Steve Lustig (Dupont)
Jim Belak and Roy Pollock (LLNL) :ul

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"Higher level section"_Intro.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
LAMMPS features :h3
LAMMPS is a classical molecular dynamics (MD) code with these general
classes of functionality:
"General features"_#general
"Particle and model types"_#particle
"Interatomic potentials (force fields)"_#ff
"Atom creation"_#create
"Ensembles, constraints, and boundary conditions"_#ensemble
"Integrators"_#integrate
"Diagnostics"_#diag
"Output"_#output
"Multi-replica models"_#replica1
"Pre- and post-processing"_#prepost
"Specialized features (beyond MD itself)"_#special :ul
:line
General features :h4,link(general)
runs on a single processor or in parallel
distributed-memory message-passing parallelism (MPI)
spatial-decomposition of simulation domain for parallelism
open-source distribution
highly portable C++
optional libraries used: MPI and single-processor FFT
GPU (CUDA and OpenCL), Intel Xeon Phi, and OpenMP support for many code features
easy to extend with new features and functionality
runs from an input script
syntax for defining and using variables and formulas
syntax for looping over runs and breaking out of loops
run one or multiple simulations simultaneously (in parallel) from one script
build as library, invoke LAMMPS through library interface or provided Python wrapper
couple with other codes: LAMMPS calls other code, other code calls LAMMPS, umbrella code calls both :ul
Particle and model types :h4,link(particle)
("atom style"_atom_style.html command)
atoms
coarse-grained particles (e.g. bead-spring polymers)
united-atom polymers or organic molecules
all-atom polymers, organic molecules, proteins, DNA
metals
granular materials
coarse-grained mesoscale models
finite-size spherical and ellipsoidal particles
finite-size line segment (2d) and triangle (3d) particles
point dipole particles
rigid collections of particles
hybrid combinations of these :ul
Interatomic potentials (force fields) :h4,link(ff)
("pair style"_pair_style.html, "bond style"_bond_style.html,
"angle style"_angle_style.html, "dihedral style"_dihedral_style.html,
"improper style"_improper_style.html, "kspace style"_kspace_style.html
commands)
pairwise potentials: Lennard-Jones, Buckingham, Morse, Born-Mayer-Huggins, \
Yukawa, soft, class 2 (COMPASS), hydrogen bond, tabulated
charged pairwise potentials: Coulombic, point-dipole
many-body potentials: EAM, Finnis/Sinclair EAM, modified EAM (MEAM), \
embedded ion method (EIM), EDIP, ADP, Stillinger-Weber, Tersoff, \
REBO, AIREBO, ReaxFF, COMB, SNAP, Streitz-Mintmire, 3-body polymorphic
long-range interactions for charge, point-dipoles, and LJ dispersion: \
Ewald, Wolf, PPPM (similar to particle-mesh Ewald)
polarization models: "QEq"_fix_qeq.html, \
"core/shell model"_Howto_coreshell.html, \
"Drude dipole model"_Howto_drude.html
charge equilibration (QEq via dynamic, point, shielded, Slater methods)
coarse-grained potentials: DPD, GayBerne, REsquared, colloidal, DLVO
mesoscopic potentials: granular, Peridynamics, SPH
electron force field (eFF, AWPMD)
bond potentials: harmonic, FENE, Morse, nonlinear, class 2, \
quartic (breakable)
angle potentials: harmonic, CHARMM, cosine, cosine/squared, cosine/periodic, \
class 2 (COMPASS)
dihedral potentials: harmonic, CHARMM, multi-harmonic, helix, \
class 2 (COMPASS), OPLS
improper potentials: harmonic, cvff, umbrella, class 2 (COMPASS)
polymer potentials: all-atom, united-atom, bead-spring, breakable
water potentials: TIP3P, TIP4P, SPC
implicit solvent potentials: hydrodynamic lubrication, Debye
force-field compatibility with common CHARMM, AMBER, DREIDING, \
OPLS, GROMACS, COMPASS options
access to the "OpenKIM Repository"_http://openkim.org of potentials via \
"kim_init, kim_interactions, and kim_query"_kim_commands.html commands
hybrid potentials: multiple pair, bond, angle, dihedral, improper \
potentials can be used in one simulation
overlaid potentials: superposition of multiple pair potentials :ul
Atom creation :h4,link(create)
("read_data"_read_data.html, "lattice"_lattice.html,
"create_atoms"_create_atoms.html, "delete_atoms"_delete_atoms.html,
"displace_atoms"_displace_atoms.html, "replicate"_replicate.html commands)
read in atom coords from files
create atoms on one or more lattices (e.g. grain boundaries)
delete geometric or logical groups of atoms (e.g. voids)
replicate existing atoms multiple times
displace atoms :ul
Ensembles, constraints, and boundary conditions :h4,link(ensemble)
("fix"_fix.html command)
2d or 3d systems
orthogonal or non-orthogonal (triclinic symmetry) simulation domains
constant NVE, NVT, NPT, NPH, Parrinello/Rahman integrators
thermostatting options for groups and geometric regions of atoms
pressure control via Nose/Hoover or Berendsen barostatting in 1 to 3 dimensions
simulation box deformation (tensile and shear)
harmonic (umbrella) constraint forces
rigid body constraints
SHAKE bond and angle constraints
Monte Carlo bond breaking, formation, swapping
atom/molecule insertion and deletion
walls of various kinds
non-equilibrium molecular dynamics (NEMD)
variety of additional boundary conditions and constraints :ul
Integrators :h4,link(integrate)
("run"_run.html, "run_style"_run_style.html, "minimize"_minimize.html commands)
velocity-Verlet integrator
Brownian dynamics
rigid body integration
energy minimization via conjugate gradient or steepest descent relaxation
rRESPA hierarchical timestepping
rerun command for post-processing of dump files :ul
Diagnostics :h4,link(diag)
see various flavors of the "fix"_fix.html and "compute"_compute.html commands :ul
Output :h4,link(output)
("dump"_dump.html, "restart"_restart.html commands)
log file of thermodynamic info
text dump files of atom coords, velocities, other per-atom quantities
binary restart files
parallel I/O of dump and restart files
per-atom quantities (energy, stress, centro-symmetry parameter, CNA, etc)
user-defined system-wide (log file) or per-atom (dump file) calculations
spatial and time averaging of per-atom quantities
time averaging of system-wide quantities
atom snapshots in native, XYZ, XTC, DCD, CFG formats :ul
Multi-replica models :h4,link(replica1)
"nudged elastic band"_neb.html
"parallel replica dynamics"_prd.html
"temperature accelerated dynamics"_tad.html
"parallel tempering"_temper.html :ul
Pre- and post-processing :h4,link(prepost)
A handful of pre- and post-processing tools are packaged with LAMMPS,
some of which can convert input and output files to/from formats used
by other codes; see the "Toos"_Tools.html doc page. :ulb,l
Our group has also written and released a separate toolkit called
"Pizza.py"_pizza which provides tools for doing setup, analysis,
plotting, and visualization for LAMMPS simulations. Pizza.py is
written in "Python"_python and is available for download from "the
Pizza.py WWW site"_pizza. :l,ule
:link(pizza,http://www.sandia.gov/~sjplimp/pizza.html)
:link(python,http://www.python.org)
Specialized features :h4,link(special)
LAMMPS can be built with optional packages which implement a variety
of additional capabilities. See the "Packages"_Packages.html doc
page for details.
These are LAMMPS capabilities which you may not think of as typical
classical MD options:
"static"_balance.html and "dynamic load-balancing"_fix_balance.html
"generalized aspherical particles"_Howto_body.html
"stochastic rotation dynamics (SRD)"_fix_srd.html
"real-time visualization and interactive MD"_fix_imd.html
calculate "virtual diffraction patterns"_compute_xrd.html
"atom-to-continuum coupling"_fix_atc.html with finite elements
coupled rigid body integration via the "POEMS"_fix_poems.html library
"QM/MM coupling"_fix_qmmm.html
Monte Carlo via "GCMC"_fix_gcmc.html and "tfMC"_fix_tfmc.html and "atom swapping"_fix_atom_swap.html
"path-integral molecular dynamics (PIMD)"_fix_ipi.html and "this as well"_fix_pimd.html
"Direct Simulation Monte Carlo"_pair_dsmc.html for low-density fluids
"Peridynamics mesoscale modeling"_pair_peri.html
"Lattice Boltzmann fluid"_fix_lb_fluid.html
"targeted"_fix_tmd.html and "steered"_fix_smd.html molecular dynamics
"two-temperature electron model"_fix_ttm.html :ul

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"Higher level section"_Intro.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
LAMMPS non-features :h3
LAMMPS is designed to be a fast, parallel engine for molecular
dynamics (MD) simulations. It provides only a modest amount of
functionality for setting up simulations and analyzing their output.
Specifically, LAMMPS was not conceived and designed for:
being run through a GUI
building molecular systems, or building molecular topologies
assign force-field coefficients automagically
perform sophisticated analysis of your MD simulation
visualize your MD simulation interactively
plot your output data :ul
Although over the years these limitations have been somewhat
reduced through features added to LAMMPS or external tools
that either closely interface with LAMMPS or extend LAMMPS.
Here are suggestions on how to perform these tasks:
[GUI:] LAMMPS can be built as a library and a Python wrapper that wraps
the library interface is provided. Thus, GUI interfaces can be
written in Python (or C or C++ if desired) that run LAMMPS and
visualize or plot its output. Examples of this are provided in the
python directory and described on the "Python"_Python_head.html doc
page. Also, there are several external wrappers or GUI front ends. :ulb,l
[Builder:] Several pre-processing tools are packaged with LAMMPS. Some
of them convert input files in formats produced by other MD codes such
as CHARMM, AMBER, or Insight into LAMMPS input formats. Some of them
are simple programs that will build simple molecular systems, such as
linear bead-spring polymer chains. The moltemplate program is a true
molecular builder that will generate complex molecular models. See
the "Tools"_Tools.html doc page for details on tools packaged with
LAMMPS. The "Pre/post processing
page"_http:/lammps.sandia.gov/prepost.html of the LAMMPS website
describes a variety of 3rd party tools for this task. Furthermore,
some LAMMPS internal commands allow to reconstruct, or selectively add
topology information, as well as provide the option to insert molecule
templates instead of atoms for building bulk molecular systems. :l
[Force-field assignment:] The conversion tools described in the previous
bullet for CHARMM, AMBER, and Insight will also assign force field
coefficients in the LAMMPS format, assuming you provide CHARMM, AMBER,
or BIOVIA (formerly Accelrys) force field files. The tools
"ParmEd"_https://parmed.github.io/ParmEd/html/index.html and
"InterMol"_https://github.com/shirtsgroup/InterMol are particularly
powerful and flexible in converting force field and topology data
between various MD simulation programs. :l
[Simulation analysis:] If you want to perform analysis on-the-fly as
your simulation runs, see the "compute"_compute.html and
"fix"_fix.html doc pages, which list commands that can be used in a
LAMMPS input script. Also see the "Modify"_Modify.html doc page for
info on how to add your own analysis code or algorithms to LAMMPS.
For post-processing, LAMMPS output such as "dump file
snapshots"_dump.html can be converted into formats used by other MD or
post-processing codes. To some degree, that conversion can be done
directly inside of LAMMPS by interfacing to the VMD molfile plugins.
The "rerun"_rerun.html command also allows to do some post-processing
of existing trajectories, and through being able to read a variety
of file formats, this can also be used for analyzing trajectories
from other MD codes. Some post-processing tools packaged with
LAMMPS will do these conversions. Scripts provided in the
tools/python directory can extract and massage data in dump files to
make it easier to import into other programs. See the
"Tools"_Tools.html doc page for details on these various options. :l
[Visualization:] LAMMPS can produce NETPBM, JPG or PNG snapshot images
on-the-fly via its "dump image"_dump_image.html command and pass
them to an external program, "FFmpeg"_https://www.ffmpeg.org to generate
movies from them. For high-quality, interactive visualization there are
many excellent and free tools available. See the "Other Codes
page"_http://lammps.sandia.gov/viz.html page of the LAMMPS website for
visualization packages that can use LAMMPS output data. :l
[Plotting:] See the next bullet about Pizza.py as well as the
"Python"_Python_head.html doc page for examples of plotting LAMMPS
output. Scripts provided with the {python} tool in the tools
directory will extract and massage data in log and dump files to make
it easier to analyze and plot. See the "Tools"_Tools.html doc page
for more discussion of the various tools. :l
[Pizza.py:] Our group has also written a separate toolkit called
"Pizza.py"_http://pizza.sandia.gov which can do certain kinds of
setup, analysis, plotting, and visualization (via OpenGL) for LAMMPS
simulations. It thus provides some functionality for several of the
above bullets. Pizza.py is written in "Python"_http://www.python.org
and is available for download from "this
page"_http://www.cs.sandia.gov/~sjplimp/download.html. :l,ule

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"Higher level section"_Intro.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
LAMMPS open-source license :h3
LAMMPS is a freely-available open-source code, distributed under the
terms of the "GNU Public License"_gnu, which means you can use or
modify the code however you wish.
LAMMPS comes with no warranty of any kind. As each source file states
in its header, it is a copyrighted code that is distributed free-of-
charge, under the terms of the "GNU Public License"_gnu (GPL). This
is often referred to as open-source distribution - see
"www.gnu.org"_gnuorg or "www.opensource.org"_opensource. The legal
text of the GPL is in the LICENSE file included in the LAMMPS
distribution.
:link(gnu,http://www.gnu.org/copyleft/gpl.html)
:link(gnuorg,http://www.gnu.org)
:link(opensource,http://www.opensource.org)
Here is a summary of what the GPL means for LAMMPS users:
(1) Anyone is free to use, modify, or extend LAMMPS in any way they
choose, including for commercial purposes.
(2) If you distribute a modified version of LAMMPS, it must remain
open-source, meaning you distribute it under the terms of the GPL.
You should clearly annotate such a code as a derivative version of
LAMMPS.
(3) If you release any code that includes LAMMPS source code, then it
must also be open-sourced, meaning you distribute it under the terms
of the GPL.
(4) If you give LAMMPS files to someone else, the GPL LICENSE file and
source file headers (including the copyright and GPL notices) should
remain part of the code.

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"Higher level section"_Intro.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Overview of LAMMPS :h3
LAMMPS is a classical molecular dynamics (MD) code that models
ensembles of particles in a liquid, solid, or gaseous state. It can
model atomic, polymeric, biological, solid-state (metals, ceramics,
oxides), granular, coarse-grained, or macroscopic systems using a
variety of interatomic potentials (force fields) and boundary
conditions. It can model 2d or 3d systems with only a few particles
up to millions or billions.
LAMMPS can be built and run on a laptop or desktop machine, but is
designed for parallel computers. It will run on any parallel machine
that supports the "MPI"_mpi message-passing library. This includes
shared-memory boxes and distributed-memory clusters and
supercomputers.
:link(mpi,http://www-unix.mcs.anl.gov/mpi)
LAMMPS is written in C++. Earlier versions were written in F77 and
F90. See the "History page"_http://lammps.sandia.gov/history.html of
the website for details. All versions can be downloaded from the
"LAMMPS website"_lws.
LAMMPS is designed to be easy to modify or extend with new
capabilities, such as new force fields, atom types, boundary
conditions, or diagnostics. See the "Modify"_Modify.html doc page for
more details.
In the most general sense, LAMMPS integrates Newton's equations of
motion for a collection of interacting particles. A single particle
can be an atom or molecule or electron, a coarse-grained cluster of
atoms, or a mesoscopic or macroscopic clump of material. The
interaction models that LAMMPS includes are mostly short-range in
nature; some long-range models are included as well.
LAMMPS uses neighbor lists to keep track of nearby particles. The
lists are optimized for systems with particles that are repulsive at
short distances, so that the local density of particles never becomes
too large. This is in contrast to methods used for modeling plasma
or gravitational bodies (e.g. galaxy formation).
On parallel machines, LAMMPS uses spatial-decomposition techniques to
partition the simulation domain into small sub-domains of equal
computational cost, one of which is assigned to each processor.
Processors communicate and store "ghost" atom information for atoms
that border their sub-domain.

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"Higher level section"_Intro.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Additional website links :h3
The "LAMMPS website"_lws has a variety of additional info about
LAMMPS, beyond what is in this manual. Some of the other pages in
this Intr are included in this list.
"Brief intro and recently added significant features"_lws
"List of features"_http://lammps.sandia.gov/features.html
"List of non-features"_http://lammps.sandia.gov/non_features.html
"Recent bug fixes and new features"_http://lammps.sandia.gov/bug.html :ul
"Download info"_http://lammps.sandia.gov/download.html
"GitHub site"_https://github.com/lammps/lammps
"SourceForge site"_https://sourceforge.net/projects/lammps
"LAMMPS open-source license"_http://lammps.sandia.gov/open_source.html :ul
"Glossary of MD terms relevant to LAMMPS"_http://lammps.sandia.gov/glossary.html
"LAMMPS highlights with images"_http://lammps.sandia.gov/pictures.html
"LAMMPS highlights with movies"_http://lammps.sandia.gov/movies.html
"Mail list"_http://lammps.sandia.gov/mail.html
"Workshops"_http://lammps.sandia.gov/workshops.html
"Tutorials"_http://lammps.sandia.gov/tutorials.html
"Developer guide"_http://lammps.sandia.gov/Developer.pdf :ul
"Pre- and post-processing tools for LAMMPS"_http://lammps.sandia.gov/prepost.html
"Other software usable with LAMMPS"_http://lammps.sandia.gov/offsite.html
"Viz tools usable with LAMMPS"_http://lammps.sandia.gov/viz.html :ul
"Benchmark performance"_http://lammps.sandia.gov/bench.html
"Publications that have cited LAMMPS"_http://lammps.sandia.gov/papers.html
"Authors of LAMMPS"_http://lammps.sandia.gov/authors.html
"History of LAMMPS development"_http://lammps.sandia.gov/history.html
"Funding for LAMMPS"_http://lammps.sandia.gov/funding.html :ul

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"Higher level section"_Manual.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
What does a LAMMPS version mean :h3
The LAMMPS "version" is the date when it was released, such as 1 May
2014. LAMMPS is updated continuously. Whenever we fix a bug or add a
feature, we release it in the next {patch} release, which are
typically made every couple of weeks. Info on patch releases are on
"this website page"_http://lammps.sandia.gov/bug.html. Every few
months, the latest patch release is subjected to more thorough testing
and labeled as a {stable} version.
Each version of LAMMPS contains all the features and bug-fixes up to
and including its version date.
The version date is printed to the screen and logfile every time you
run LAMMPS. It is also in the file src/version.h and in the LAMMPS
directory name created when you unpack a tarball. And it is on the
first page of the "manual"_Manual.html.
If you browse the HTML doc pages on the LAMMPS WWW site, they always
describe the most current patch release of LAMMPS. :ulb,l
If you browse the HTML doc pages included in your tarball, they
describe the version you have, which may be older. :l,ule

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"Previous Section"_Tools.html - "LAMMPS WWW Site"_lws -
"LAMMPS Documentation"_ld - "LAMMPS Commands"_lc - "Next
Section"_Python_head.html :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Modify & extend LAMMPS :h2
LAMMPS is designed in a modular fashion so as to be easy to modify and
extend with new functionality. In fact, about 95% of its source code
is add-on files. These doc pages give basic instructions on how to do
this.
If you add a new feature to LAMMPS and think it will be of interest to
general users, we encourage you to submit it for inclusion in LAMMPS
as a pull request on our "GitHub
site"_https://github.com/lammps/lammps, after reading the "Modify
contribute"_Modify_contribute.html doc page.
<!-- RST
.. toctree::
:maxdepth: 1
Modify_overview
Modify_contribute
.. toctree::
:maxdepth: 1
Modify_atom
Modify_pair
Modify_bond
Modify_compute
Modify_fix
Modify_command
Modify_dump
Modify_kspace
Modify_min
Modify_region
Modify_body
Modify_thermo
Modify_variable
END_RST -->
<!-- HTML_ONLY -->
"Overview"_Modify_overview.html
"Submitting new features for inclusion in LAMMPS"_Modify_contribute.html :all(b)
"Atom styles"_Modify_atom.html
"Pair styles"_Modify_pair.html
"Bond, angle, dihedral, improper styles"_Modify_bond.html
"Compute styles"_Modify_compute.html
"Fix styles"_Modify_fix.html
"Input script command styles"_Modify_command.html
"Dump styles"_Modify_dump.html
"Kspace styles"_Modify_kspace.html
"Minimization styles"_Modify_min.html
"Region styles"_Modify_region.html
"Body styles"_Modify_body.html
"Thermodynamic output options"_Modify_thermo.html
"Variable options"_Modify_variable.html :all(b)
<!-- END_HTML_ONLY -->

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"Higher level section"_Modify.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Atom styles :h3
Classes that define an "atom style"_atom_style.html are derived from
the AtomVec class and managed by the Atom class. The atom style
determines what attributes are associated with an atom. A new atom
style can be created if one of the existing atom styles does not
define all the attributes you need to store and communicate with
atoms.
Atom_vec_atomic.cpp is a simple example of an atom style.
Here is a brief description of methods you define in your new derived
class. See atom_vec.h for details.
init: one time setup (optional)
grow: re-allocate atom arrays to longer lengths (required)
grow_reset: make array pointers in Atom and AtomVec classes consistent (required)
copy: copy info for one atom to another atom's array locations (required)
pack_comm: store an atom's info in a buffer communicated every timestep (required)
pack_comm_vel: add velocity info to communication buffer (required)
pack_comm_hybrid: store extra info unique to this atom style (optional)
unpack_comm: retrieve an atom's info from the buffer (required)
unpack_comm_vel: also retrieve velocity info (required)
unpack_comm_hybrid: retrieve extra info unique to this atom style (optional)
pack_reverse: store an atom's info in a buffer communicating partial forces (required)
pack_reverse_hybrid: store extra info unique to this atom style (optional)
unpack_reverse: retrieve an atom's info from the buffer (required)
unpack_reverse_hybrid: retrieve extra info unique to this atom style (optional)
pack_border: store an atom's info in a buffer communicated on neighbor re-builds (required)
pack_border_vel: add velocity info to buffer (required)
pack_border_hybrid: store extra info unique to this atom style (optional)
unpack_border: retrieve an atom's info from the buffer (required)
unpack_border_vel: also retrieve velocity info (required)
unpack_border_hybrid: retrieve extra info unique to this atom style (optional)
pack_exchange: store all an atom's info to migrate to another processor (required)
unpack_exchange: retrieve an atom's info from the buffer (required)
size_restart: number of restart quantities associated with proc's atoms (required)
pack_restart: pack atom quantities into a buffer (required)
unpack_restart: unpack atom quantities from a buffer (required)
create_atom: create an individual atom of this style (required)
data_atom: parse an atom line from the data file (required)
data_atom_hybrid: parse additional atom info unique to this atom style (optional)
data_vel: parse one line of velocity information from data file (optional)
data_vel_hybrid: parse additional velocity data unique to this atom style (optional)
memory_usage: tally memory allocated by atom arrays (required) :tb(s=:)
The constructor of the derived class sets values for several variables
that you must set when defining a new atom style, which are documented
in atom_vec.h. New atom arrays are defined in atom.cpp. Search for
the word "customize" and you will find locations you will need to
modify.
NOTE: It is possible to add some attributes, such as a molecule ID, to
atom styles that do not have them via the "fix
property/atom"_fix_property_atom.html command. This command also
allows new custom attributes consisting of extra integer or
floating-point values to be added to atoms. See the "fix
property/atom"_fix_property_atom.html doc page for examples of cases
where this is useful and details on how to initialize, access, and
output the custom values.
New "pair styles"_pair_style.html, "fixes"_fix.html, or
"computes"_compute.html can be added to LAMMPS, as discussed below.
The code for these classes can use the per-atom properties defined by
fix property/atom. The Atom class has a find_custom() method that is
useful in this context:
int index = atom->find_custom(char *name, int &flag); :pre
The "name" of a custom attribute, as specified in the "fix
property/atom"_fix_property_atom.html command, is checked to verify
that it exists and its index is returned. The method also sets flag =
0/1 depending on whether it is an integer or floating-point attribute.
The vector of values associated with the attribute can then be
accessed using the returned index as
int *ivector = atom->ivector\[index\];
double *dvector = atom->dvector\[index\]; :pre
Ivector or dvector are vectors of length Nlocal = # of owned atoms,
which store the attributes of individual atoms.

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"Higher level section"_Modify.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Body styles :h3
Classes that define body particles are derived from the Body class.
Body particles can represent complex entities, such as surface meshes
of discrete points, collections of sub-particles, deformable objects,
etc.
See the "Howto body"_Howto_body.html doc page for an overview of using
body particles and the various body styles LAMMPS supports. New
styles can be created to add new kinds of body particles to LAMMPS.
Body_nparticle.cpp is an example of a body particle that is treated as
a rigid body containing N sub-particles.
Here is a brief description of methods you define in your new derived
class. See body.h for details.
data_body: process a line from the Bodies section of a data file
noutrow: number of sub-particles output is generated for
noutcol: number of values per-sub-particle output is generated for
output: output values for the Mth sub-particle
pack_comm_body: body attributes to communicate every timestep
unpack_comm_body: unpacking of those attributes
pack_border_body: body attributes to communicate when reneighboring is done
unpack_border_body: unpacking of those attributes :tb(s=:)

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"Higher level section"_Modify.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Bond, angle, dihedral, improper styles :h3
Classes that compute molecular interactions are derived from the Bond,
Angle, Dihedral, and Improper classes. New styles can be created to
add new potentials to LAMMPS.
Bond_harmonic.cpp is the simplest example of a bond style. Ditto for
the harmonic forms of the angle, dihedral, and improper style
commands.
Here is a brief description of common methods you define in your
new derived class. See bond.h, angle.h, dihedral.h, and improper.h
for details and specific additional methods.
init: check if all coefficients are set, calls {init_style} (optional)
init_style: check if style specific conditions are met (optional)
compute: compute the molecular interactions (required)
settings: apply global settings for all types (optional)
coeff: set coefficients for one type (required)
equilibrium_distance: length of bond, used by SHAKE (required, bond only)
equilibrium_angle: opening of angle, used by SHAKE (required, angle only)
write & read_restart: writes/reads coeffs to restart files (required)
single: force and energy of a single bond or angle (required, bond or angle only)
memory_usage: tally memory allocated by the style (optional) :tb(s=:)

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"Higher level section"_Modify.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Input script command style :h3
New commands can be added to LAMMPS input scripts by adding new
classes that have a "command" method. For example, the create_atoms,
read_data, velocity, and run commands are all implemented in this
fashion. When such a command is encountered in the LAMMPS input
script, LAMMPS simply creates a class with the corresponding name,
invokes the "command" method of the class, and passes it the arguments
from the input script. The command method can perform whatever
operations it wishes on LAMMPS data structures.
The single method your new class must define is as follows:
command: operations performed by the new command :tb(s=:)
Of course, the new class can define other methods and variables as
needed.

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"Higher level section"_Modify.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Compute styles :h3
Classes that compute scalar and vector quantities like temperature
and the pressure tensor, as well as classes that compute per-atom
quantities like kinetic energy and the centro-symmetry parameter
are derived from the Compute class. New styles can be created
to add new calculations to LAMMPS.
Compute_temp.cpp is a simple example of computing a scalar
temperature. Compute_ke_atom.cpp is a simple example of computing
per-atom kinetic energy.
Here is a brief description of methods you define in your new derived
class. See compute.h for details.
init: perform one time setup (required)
init_list: neighbor list setup, if needed (optional)
compute_scalar: compute a scalar quantity (optional)
compute_vector: compute a vector of quantities (optional)
compute_peratom: compute one or more quantities per atom (optional)
compute_local: compute one or more quantities per processor (optional)
pack_comm: pack a buffer with items to communicate (optional)
unpack_comm: unpack the buffer (optional)
pack_reverse: pack a buffer with items to reverse communicate (optional)
unpack_reverse: unpack the buffer (optional)
remove_bias: remove velocity bias from one atom (optional)
remove_bias_all: remove velocity bias from all atoms in group (optional)
restore_bias: restore velocity bias for one atom after remove_bias (optional)
restore_bias_all: same as before, but for all atoms in group (optional)
pair_tally_callback: callback function for {tally}-style computes (optional).
memory_usage: tally memory usage (optional) :tb(s=:)
Tally-style computes are a special case, as their computation is done
in two stages: the callback function is registered with the pair style
and then called from the Pair::ev_tally() function, which is called for
each pair after force and energy has been computed for this pair. Then
the tallied values are retrieved with the standard compute_scalar or
compute_vector or compute_peratom methods. The USER-TALLY package
provides {examples}_compute_tally.html for utilizing this mechanism.

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"Higher level section"_Modify.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Submitting new features for inclusion in LAMMPS :h3
We encourage users to submit new features or modifications for LAMMPS
to "the core developers"_http://lammps.sandia.gov/authors.html so they
can be added to the LAMMPS distribution. The preferred way to manage
and coordinate this is as of Fall 2016 via the LAMMPS project on
"GitHub"_https://github.com/lammps/lammps. An alternative is to
contact the LAMMPS developers or the indicated developer of a package
or feature directly and send in your contribution via e-mail.
For any larger modifications or programming project, you are
encouraged to contact the LAMMPS developers ahead of time, in order to
discuss implementation strategies and coding guidelines, that will
make it easier to integrate your contribution and result in less work
for everybody involved. You are also encouraged to search through the
list of "open issues on
GitHub"_https://github.com/lammps/lammps/issues and submit a new issue
for a planned feature, so you would not duplicate the work of others
(and possibly get scooped by them) or have your work duplicated by
others.
How quickly your contribution will be integrated depends largely on
how much effort it will cause to integrate and test it, how much it
requires changes to the core codebase, and of how much interest it is
to the larger LAMMPS community. Please see below for a checklist of
typical requirements. Once you have prepared everything, see the
"Using GitHub with LAMMPS Howto"_Howto_github.html doc page for instructions on how to
submit your changes or new files through a GitHub pull request. If you
prefer to submit patches or full files, you should first make certain,
that your code works correctly with the latest patch-level version of
LAMMPS and contains all bug fixes from it. Then create a gzipped tar
file of all changed or added files or a corresponding patch file using
'diff -u' or 'diff -c' and compress it with gzip. Please only use gzip
compression, as this works well on all platforms.
If the new features/files are broadly useful we may add them as core
files to LAMMPS or as part of a "standard
package"_Packages_standard.html. Else we will add them as a
user-contributed file or "user package"_Packages_user.html. Examples
of user packages are in src sub-directories that start with USER. The
USER-MISC package is simply a collection of (mostly) unrelated single
files, which is the simplest way to have your contribution quickly
added to the LAMMPS distribution. All the standard and user packages
are listed and described on the "Packages
details"_Packages_details.html doc page.
Note that by providing us files to release, you are agreeing to make
them open-source, i.e. we can release them under the terms of the GPL,
used as a license for the rest of LAMMPS. See the "Open
source"_http://lammps.sandia.gov/open_source.html page on the LAMMPS
website for details.
With user packages and files, all we are really providing (aside from
the fame and fortune that accompanies having your name in the source
code and on the "Authors page"_http://lammps.sandia.gov/authors.html
of the "LAMMPS WWW site"_lws), is a means for you to distribute your
work to the LAMMPS user community, and a mechanism for others to
easily try out your new feature. This may help you find bugs or make
contact with new collaborators. Note that you're also implicitly
agreeing to support your code which means answer questions, fix bugs,
and maintain it if LAMMPS changes in some way that breaks it (an
unusual event).
NOTE: If you prefer to actively develop and support your add-on
feature yourself, then you may wish to make it available for download
from your own website, as a user package that LAMMPS users can add to
their copy of LAMMPS. See the "Offsite LAMMPS packages and
tools"_http://lammps.sandia.gov/offsite.html page of the LAMMPS web
site for examples of groups that do this. We are happy to advertise
your package and web site from that page. Simply email the
"developers"_http://lammps.sandia.gov/authors.html with info about
your package and we will post it there.
The previous sections of this doc page describe how to add new "style"
files of various kinds to LAMMPS. Packages are simply collections of
one or more new class files which are invoked as a new style within a
LAMMPS input script. If designed correctly, these additions typically
do not require changes to the main core of LAMMPS; they are simply
add-on files. If you think your new feature requires non-trivial
changes in core LAMMPS files, you'll need to "communicate with the
developers"_http://lammps.sandia.gov/authors.html, since we may or may
not want to make those changes. An example of a trivial change is
making a parent-class method "virtual" when you derive a new child
class from it.
Here is a checklist of steps you need to follow to submit a single file
or user package for our consideration. Following these steps will save
both you and us time. See existing files in packages in the src dir for
examples. If you are uncertain, please ask.
All source files you provide must compile with the most current
version of LAMMPS with multiple configurations. In particular you
need to test compiling LAMMPS from scratch with -DLAMMPS_BIGBIG
set in addition to the default -DLAMMPS_SMALLBIG setting. Your code
will need to work correctly in serial and in parallel using MPI. :ulb,l
For consistency with the rest of LAMMPS and especially, if you want
your contribution(s) to be added to main LAMMPS code or one of its
standard packages, it needs to be written in a style compatible with
other LAMMPS source files. This means: 2-character indentation per
level, [no tabs], no lines over 80 characters. I/O is done via
the C-style stdio library (mixing of stdio and iostreams is generally
discouraged), class header files should not import any system headers
outside of <cstdio>, STL containers should be avoided in headers,
system header from the C library should use the C++-style names
(<cstdlib>, <cstdio>, or <cstring>) instead of the C-style names
<stdlib.h>, <stdio.h>, or <string.h>), and forward declarations
used where possible or needed to avoid including headers.
All added code should be placed into the LAMMPS_NS namespace or a
sub-namespace; global or static variables should be avoided, as they
conflict with the modular nature of LAMMPS and the C++ class structure.
Header files must [not] import namespaces with {using}.
This all is so the developers can more easily understand, integrate,
and maintain your contribution and reduce conflicts with other parts
of LAMMPS. This basically means that the code accesses data
structures, performs its operations, and is formatted similar to other
LAMMPS source files, including the use of the error class for error
and warning messages. :l
If you want your contribution to be added as a user-contributed
feature, and it's a single file (actually a *.cpp and *.h file) it can
rapidly be added to the USER-MISC directory. Send us the one-line
entry to add to the USER-MISC/README file in that dir, along with the
2 source files. You can do this multiple times if you wish to
contribute several individual features. :l
If you want your contribution to be added as a user-contribution and
it is several related features, it is probably best to make it a user
package directory with a name like USER-FOO. In addition to your new
files, the directory should contain a README text file. The README
should contain your name and contact information and a brief
description of what your new package does. If your files depend on
other LAMMPS style files also being installed (e.g. because your file
is a derived class from the other LAMMPS class), then an Install.sh
file is also needed to check for those dependencies. See other README
and Install.sh files in other USER directories as examples. Send us a
tarball of this USER-FOO directory. :l
Your new source files need to have the LAMMPS copyright, GPL notice,
and your name and email address at the top, like other
user-contributed LAMMPS source files. They need to create a class
that is inside the LAMMPS namespace. If the file is for one of the
USER packages, including USER-MISC, then we are not as picky about the
coding style (see above). I.e. the files do not need to be in the
same stylistic format and syntax as other LAMMPS files, though that
would be nice for developers as well as users who try to read your
code. :l
You [must] also create a [documentation] file for each new command or
style you are adding to LAMMPS. For simplicity and convenience, the
documentation of groups of closely related commands or styles may be
combined into a single file. This will be one file for a single-file
feature. For a package, it might be several files. These are simple
text files with a specific markup language, that are then auto-converted
to HTML and PDF. The tools for this conversion are included in the
source distribution, and the translation can be as simple as doing
"make html pdf" in the doc folder.
Thus the documentation source files must be in the same format and
style as other *.txt files in the lammps/doc/src directory for similar
commands and styles; use one or more of them as a starting point.
A description of the markup can also be found in
lammps/doc/utils/txt2html/README.html
As appropriate, the text files can include links to equations
(see doc/Eqs/*.tex for examples, we auto-create the associated JPG
files), or figures (see doc/JPG for examples), or even additional PDF
files with further details (see doc/PDF for examples). The doc page
should also include literature citations as appropriate; see the
bottom of doc/fix_nh.txt for examples and the earlier part of the same
file for how to format the cite itself. The "Restrictions" section of
the doc page should indicate that your command is only available if
LAMMPS is built with the appropriate USER-MISC or USER-FOO package.
See other user package doc files for examples of how to do this. The
prerequisite for building the HTML format files are Python 3.x and
virtualenv, the requirement for generating the PDF format manual
is the "htmldoc"_http://www.htmldoc.org/ software. Please run at least
"make html" and carefully inspect and proofread the resulting HTML format
doc page before submitting your code. :l
For a new package (or even a single command) you should include one or
more example scripts demonstrating its use. These should run in no
more than a couple minutes, even on a single processor, and not require
large data files as input. See directories under examples/USER for
examples of input scripts other users provided for their packages.
These example inputs are also required for validating memory accesses
and testing for memory leaks with valgrind :l
If there is a paper of yours describing your feature (either the
algorithm/science behind the feature itself, or its initial usage, or
its implementation in LAMMPS), you can add the citation to the *.cpp
source file. See src/USER-EFF/atom_vec_electron.cpp for an example.
A LaTeX citation is stored in a variable at the top of the file and a
single line of code that references the variable is added to the
constructor of the class. Whenever a user invokes your feature from
their input script, this will cause LAMMPS to output the citation to a
log.cite file and prompt the user to examine the file. Note that you
should only use this for a paper you or your group authored.
E.g. adding a cite in the code for a paper by Nose and Hoover if you
write a fix that implements their integrator is not the intended
usage. That kind of citation should just be in the doc page you
provide. :l
:ule
Finally, as a general rule-of-thumb, the more clear and
self-explanatory you make your documentation and README files, and the
easier you make it for people to get started, e.g. by providing example
scripts, the more likely it is that users will try out your new feature.

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"Higher level section"_Modify.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Dump styles :h3
Classes that dump per-atom info to files are derived from the Dump
class. To dump new quantities or in a new format, a new derived dump
class can be added, but it is typically simpler to modify the
DumpCustom class contained in the dump_custom.cpp file.
Dump_atom.cpp is a simple example of a derived dump class.
Here is a brief description of methods you define in your new derived
class. See dump.h for details.
write_header: write the header section of a snapshot of atoms
count: count the number of lines a processor will output
pack: pack a proc's output data into a buffer
write_data: write a proc's data to a file :tb(s=:)
See the "dump"_dump.html command and its {custom} style for a list of
keywords for atom information that can already be dumped by
DumpCustom. It includes options to dump per-atom info from Compute
classes, so adding a new derived Compute class is one way to calculate
new quantities to dump.
Note that new keywords for atom properties are not typically
added to the "dump custom"_dump.html command. Instead they are added
to the "compute property/atom"_compute_property_atom.html command.

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"Higher level section"_Modify.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Fix styles :h3
In LAMMPS, a "fix" is any operation that is computed during
timestepping that alters some property of the system. Essentially
everything that happens during a simulation besides force computation,
neighbor list construction, and output, is a "fix". This includes
time integration (update of coordinates and velocities), force
constraints or boundary conditions (SHAKE or walls), and diagnostics
(compute a diffusion coefficient). New styles can be created to add
new options to LAMMPS.
Fix_setforce.cpp is a simple example of setting forces on atoms to
prescribed values. There are dozens of fix options already in LAMMPS;
choose one as a template that is similar to what you want to
implement.
Here is a brief description of methods you can define in your new
derived class. See fix.h for details.
setmask: determines when the fix is called during the timestep (required)
init: initialization before a run (optional)
setup_pre_exchange: called before atom exchange in setup (optional)
setup_pre_force: called before force computation in setup (optional)
setup: called immediately before the 1st timestep and after forces are computed (optional)
min_setup_pre_force: like setup_pre_force, but for minimizations instead of MD runs (optional)
min_setup: like setup, but for minimizations instead of MD runs (optional)
initial_integrate: called at very beginning of each timestep (optional)
pre_exchange: called before atom exchange on re-neighboring steps (optional)
pre_neighbor: called before neighbor list build (optional)
pre_force: called before pair & molecular forces are computed (optional)
post_force: called after pair & molecular forces are computed and communicated (optional)
final_integrate: called at end of each timestep (optional)
end_of_step: called at very end of timestep (optional)
write_restart: dumps fix info to restart file (optional)
restart: uses info from restart file to re-initialize the fix (optional)
grow_arrays: allocate memory for atom-based arrays used by fix (optional)
copy_arrays: copy atom info when an atom migrates to a new processor (optional)
pack_exchange: store atom's data in a buffer (optional)
unpack_exchange: retrieve atom's data from a buffer (optional)
pack_restart: store atom's data for writing to restart file (optional)
unpack_restart: retrieve atom's data from a restart file buffer (optional)
size_restart: size of atom's data (optional)
maxsize_restart: max size of atom's data (optional)
setup_pre_force_respa: same as setup_pre_force, but for rRESPA (optional)
initial_integrate_respa: same as initial_integrate, but for rRESPA (optional)
post_integrate_respa: called after the first half integration step is done in rRESPA (optional)
pre_force_respa: same as pre_force, but for rRESPA (optional)
post_force_respa: same as post_force, but for rRESPA (optional)
final_integrate_respa: same as final_integrate, but for rRESPA (optional)
min_pre_force: called after pair & molecular forces are computed in minimizer (optional)
min_post_force: called after pair & molecular forces are computed and communicated in minimizer (optional)
min_store: store extra data for linesearch based minimization on a LIFO stack (optional)
min_pushstore: push the minimization LIFO stack one element down (optional)
min_popstore: pop the minimization LIFO stack one element up (optional)
min_clearstore: clear minimization LIFO stack (optional)
min_step: reset or move forward on line search minimization (optional)
min_dof: report number of degrees of freedom {added} by this fix in minimization (optional)
max_alpha: report maximum allowed step size during linesearch minimization (optional)
pack_comm: pack a buffer to communicate a per-atom quantity (optional)
unpack_comm: unpack a buffer to communicate a per-atom quantity (optional)
pack_reverse_comm: pack a buffer to reverse communicate a per-atom quantity (optional)
unpack_reverse_comm: unpack a buffer to reverse communicate a per-atom quantity (optional)
dof: report number of degrees of freedom {removed} by this fix during MD (optional)
compute_scalar: return a global scalar property that the fix computes (optional)
compute_vector: return a component of a vector property that the fix computes (optional)
compute_array: return a component of an array property that the fix computes (optional)
deform: called when the box size is changed (optional)
reset_target: called when a change of the target temperature is requested during a run (optional)
reset_dt: is called when a change of the time step is requested during a run (optional)
modify_param: called when a fix_modify request is executed (optional)
memory_usage: report memory used by fix (optional)
thermo: compute quantities for thermodynamic output (optional) :tb(s=:)
Typically, only a small fraction of these methods are defined for a
particular fix. Setmask is mandatory, as it determines when the fix
will be invoked during the timestep. Fixes that perform time
integration ({nve}, {nvt}, {npt}) implement initial_integrate() and
final_integrate() to perform velocity Verlet updates. Fixes that
constrain forces implement post_force().
Fixes that perform diagnostics typically implement end_of_step(). For
an end_of_step fix, one of your fix arguments must be the variable
"nevery" which is used to determine when to call the fix and you must
set this variable in the constructor of your fix. By convention, this
is the first argument the fix defines (after the ID, group-ID, style).
If the fix needs to store information for each atom that persists from
timestep to timestep, it can manage that memory and migrate the info
with the atoms as they move from processors to processor by
implementing the grow_arrays, copy_arrays, pack_exchange, and
unpack_exchange methods. Similarly, the pack_restart and
unpack_restart methods can be implemented to store information about
the fix in restart files. If you wish an integrator or force
constraint fix to work with rRESPA (see the "run_style"_run_style.html
command), the initial_integrate, post_force_integrate, and
final_integrate_respa methods can be implemented. The thermo method
enables a fix to contribute values to thermodynamic output, as printed
quantities and/or to be summed to the potential energy of the system.

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"Higher level section"_Modify.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Kspace styles :h3
Classes that compute long-range Coulombic interactions via K-space
representations (Ewald, PPPM) are derived from the KSpace class. New
styles can be created to add new K-space options to LAMMPS.
Ewald.cpp is an example of computing K-space interactions.
Here is a brief description of methods you define in your new derived
class. See kspace.h for details.
init: initialize the calculation before a run
setup: computation before the 1st timestep of a run
compute: every-timestep computation
memory_usage: tally of memory usage :tb(s=:)

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"Higher level section"_Modify.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Minimization styles :h3
Classes that perform energy minimization derived from the Min class.
New styles can be created to add new minimization algorithms to
LAMMPS.
Min_cg.cpp is an example of conjugate gradient minimization.
Here is a brief description of methods you define in your new derived
class. See min.h for details.
init: initialize the minimization before a run
run: perform the minimization
memory_usage: tally of memory usage :tb(s=:)

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"Higher level section"_Modify.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Overview :h3
The best way to add a new feature to LAMMPS is to find a similar
feature and look at the corresponding source and header files to figure
out what it does. You will need some knowledge of C++ to be able to
understand the hi-level structure of LAMMPS and its class
organization, but functions (class methods) that do actual
computations are written in vanilla C-style code and operate on simple
C-style data structures (vectors and arrays).
Most of the new features described on the "Modify"_Modify.html doc
page require you to write a new C++ derived class (except for
exceptions described below, where you can make small edits to existing
files). Creating a new class requires 2 files, a source code file
(*.cpp) and a header file (*.h). The derived class must provide
certain methods to work as a new option. Depending on how different
your new feature is compared to existing features, you can either
derive from the base class itself, or from a derived class that
already exists. Enabling LAMMPS to invoke the new class is as simple
as putting the two source files in the src dir and re-building LAMMPS.
The advantage of C++ and its object-orientation is that all the code
and variables needed to define the new feature are in the 2 files you
write, and thus shouldn't make the rest of LAMMPS more complex or
cause side-effect bugs.
Here is a concrete example. Suppose you write 2 files pair_foo.cpp
and pair_foo.h that define a new class PairFoo that computes pairwise
potentials described in the classic 1997 "paper"_#Foo by Foo, et al.
If you wish to invoke those potentials in a LAMMPS input script with a
command like
pair_style foo 0.1 3.5 :pre
then your pair_foo.h file should be structured as follows:
#ifdef PAIR_CLASS
PairStyle(foo,PairFoo)
#else
...
(class definition for PairFoo)
...
#endif :pre
where "foo" is the style keyword in the pair_style command, and
PairFoo is the class name defined in your pair_foo.cpp and pair_foo.h
files.
When you re-build LAMMPS, your new pairwise potential becomes part of
the executable and can be invoked with a pair_style command like the
example above. Arguments like 0.1 and 3.5 can be defined and
processed by your new class.
As illustrated by this pairwise example, many kinds of options are
referred to in the LAMMPS documentation as the "style" of a particular
command.
The "Modify page"_Modify.html lists all the common styles in LAMMPS,
and discusses the header file for the base class that these styles are
derived from. Public variables in that file are ones used and set by
the derived classes which are also used by the base class. Sometimes
they are also used by the rest of LAMMPS. Virtual functions in the
base class header file which are set = 0 are ones you must define in
your new derived class to give it the functionality LAMMPS expects.
Virtual functions that are not set to 0 are functions you can
optionally define.
Additionally, new output options can be added directly to the
thermo.cpp, dump_custom.cpp, and variable.cpp files. These are also
listed on the "Modify page"_Modify.html.
Here are additional guidelines for modifying LAMMPS and adding new
functionality:
Think about whether what you want to do would be better as a pre- or
post-processing step. Many computations are more easily and more
quickly done that way. :ulb,l
Don't do anything within the timestepping of a run that isn't
parallel. E.g. don't accumulate a bunch of data on a single processor
and analyze it. You run the risk of seriously degrading the parallel
efficiency. :l
If your new feature reads arguments or writes output, make sure you
follow the unit conventions discussed by the "units"_units.html
command. :l
:ule
:line
:link(Foo)
[(Foo)] Foo, Morefoo, and Maxfoo, J of Classic Potentials, 75, 345 (1997).

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"Higher level section"_Modify.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Pair styles :h3
Classes that compute pairwise interactions are derived from the Pair
class. In LAMMPS, pairwise calculation include many-body potentials
such as EAM or Tersoff where particles interact without a static bond
topology. New styles can be created to add new pair potentials to
LAMMPS.
Pair_lj_cut.cpp is a simple example of a Pair class, though it
includes some optional methods to enable its use with rRESPA.
Here is a brief description of the class methods in pair.h:
compute: workhorse routine that computes pairwise interactions
settings: reads the input script line with arguments you define
coeff: set coefficients for one i,j type pair
init_one: perform initialization for one i,j type pair
init_style: initialization specific to this pair style
write & read_restart: write/read i,j pair coeffs to restart files
write & read_restart_settings: write/read global settings to restart files
single: force and energy of a single pairwise interaction between 2 atoms
compute_inner/middle/outer: versions of compute used by rRESPA :tb(s=:)
The inner/middle/outer routines are optional.

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"Higher level section"_Modify.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Region styles :h3
Classes that define geometric regions are derived from the Region
class. Regions are used elsewhere in LAMMPS to group atoms, delete
atoms to create a void, insert atoms in a specified region, etc. New
styles can be created to add new region shapes to LAMMPS.
Region_sphere.cpp is an example of a spherical region.
Here is a brief description of methods you define in your new derived
class. See region.h for details.
inside: determine whether a point is in the region
surface_interior: determine if a point is within a cutoff distance inside of surface
surface_exterior: determine if a point is within a cutoff distance outside of surface
shape_update : change region shape if set by time-dependent variable :tb(s=:)

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"Higher level section"_Modify.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Thermodynamic output options :h3
There is one class that computes and prints thermodynamic information
to the screen and log file; see the file thermo.cpp.
There are two styles defined in thermo.cpp: "one" and "multi". There
is also a flexible "custom" style which allows the user to explicitly
list keywords for quantities to print when thermodynamic info is
output. See the "thermo_style"_thermo_style.html command for a list
of defined quantities.
The thermo styles (one, multi, etc) are simply lists of keywords.
Adding a new style thus only requires defining a new list of keywords.
Search for the word "customize" with references to "thermo style" in
thermo.cpp to see the two locations where code will need to be added.
New keywords can also be added to thermo.cpp to compute new quantities
for output. Search for the word "customize" with references to
"keyword" in thermo.cpp to see the several locations where code will
need to be added.
Note that the "thermo_style custom"_thermo.html command already allows
for thermo output of quantities calculated by "fixes"_fix.html,
"computes"_compute.html, and "variables"_variable.html. Thus, it may
be simpler to compute what you wish via one of those constructs, than
by adding a new keyword to the thermo command.

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"Higher level section"_Modify.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Variable options :h3
There is one class that computes and stores "variable"_variable.html
information in LAMMPS; see the file variable.cpp. The value
associated with a variable can be periodically printed to the screen
via the "print"_print.html, "fix print"_fix_print.html, or
"thermo_style custom"_thermo_style.html commands. Variables of style
"equal" can compute complex equations that involve the following types
of arguments:
thermo keywords = ke, vol, atoms, ...
other variables = v_a, v_myvar, ...
math functions = div(x,y), mult(x,y), add(x,y), ...
group functions = mass(group), xcm(group,x), ...
atom values = x\[123\], y\[3\], vx\[34\], ...
compute values = c_mytemp\[0\], c_thermo_press\[3\], ... :pre
Adding keywords for the "thermo_style custom"_thermo_style.html
command (which can then be accessed by variables) is discussed on the
"Modify thermo"_Modify_thermo.html doc page.
Adding a new math function of one or two arguments can be done by
editing one section of the Variable::evaluate() method. Search for
the word "customize" to find the appropriate location.
Adding a new group function can be done by editing one section of the
Variable::evaluate() method. Search for the word "customize" to find
the appropriate location. You may need to add a new method to the
Group class as well (see the group.cpp file).
Accessing a new atom-based vector can be done by editing one section
of the Variable::evaluate() method. Search for the word "customize"
to find the appropriate location.
Adding new "compute styles"_compute.html (whose calculated values can
then be accessed by variables) is discussed on the "Modify
compute"_Modify_compute.html doc page.

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"Previous Section"_Commands.html - "LAMMPS WWW Site"_lws -
"LAMMPS Documentation"_ld - "LAMMPS Commands"_lc - "Next
Section"_Speed.html :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Optional packages :h2
This section gives an overview of the optional packages that extend
LAMMPS functionality. Packages are groups of files that enable a
specific set of features. For example, force fields for molecular
systems or rigid-body constraints are in packages. You can see the
list of all packages and "make" commands to manage them by typing
"make package" from within the src directory of the LAMMPS
distribution. The "Build package"_Build_package.html doc page gives
general info on how to install and un-install packages as part of the
LAMMPS build process.
<!-- RST
.. toctree::
:maxdepth: 1
Packages_standard
Packages_user
Packages_details
END_RST -->
<!-- HTML_ONLY -->
"Standard packages"_Packages_standard.html
"User packages"_Packages_user.html
"Details on each package"_Packages_details.html :ul
<!-- END_HTML_ONLY -->

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"Higher level section"_Packages.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Standard packages :h3
This is the list of standard packages in LAMMPS. The link for each
package name gives more details.
Standard packages are supported by the LAMMPS developers and are
written in a syntax and style consistent with the rest of LAMMPS.
This means the developers will answer questions about them, debug and
fix them if necessary, and keep them compatible with future changes to
LAMMPS.
The "Example" column is a sub-directory in the examples directory of
the distribution which has an input script that uses the package.
E.g. "peptide" refers to the examples/peptide directory; USER/atc
refers to the examples/USER/atc directory. The "Library" column
indicates whether an extra library is needed to build and use the
package:
no = no library
sys = system library: you likely have it on your machine
int = internal library: provided with LAMMPS, but you may need to build it
ext = external library: you will need to download and install it on your machine :ul
Package, Description, Doc page, Example, Library
"ASPHERE"_Packages_details.html#PKG-ASPHERE, aspherical particle models, "Howto spherical"_Howto_spherical.html, ellipse, no
"BODY"_Packages_details.html#PKG-BODY, body-style particles, "Howto body"_Howto_body.html, body, no
"CLASS2"_Packages_details.html#PKG-CLASS2, class 2 force fields, "pair_style lj/class2"_pair_class2.html, n/a, no
"COLLOID"_Packages_details.html#PKG-COLLOID, colloidal particles, "atom_style colloid"_atom_style.html, colloid, no
"COMPRESS"_Packages_details.html#PKG-COMPRESS, I/O compression, "dump */gz"_dump.html, n/a, sys
"CORESHELL"_Packages_details.html#PKG-CORESHELL, adiabatic core/shell model, "Howto coreshell"_Howto_coreshell.html, coreshell, no
"DIPOLE"_Packages_details.html#PKG-DIPOLE, point dipole particles, "pair_style dipole/cut"_pair_dipole.html, dipole, no
"GPU"_Packages_details.html#PKG-GPU, GPU-enabled styles, "Section gpu"_Speed_gpu.html, "Benchmarks"_http://lammps.sandia.gov/bench.html, int
"GRANULAR"_Packages_details.html#PKG-GRANULAR, granular systems, "Howto granular"_Howto_granular.html, pour, no
"KIM"_Packages_details.html#PKG-KIM, OpenKIM wrapper, "pair_style kim"_pair_kim.html, kim, ext
"KOKKOS"_Packages_details.html#PKG-KOKKOS, Kokkos-enabled styles, "Speed kokkos"_Speed_kokkos.html, "Benchmarks"_http://lammps.sandia.gov/bench.html, no
"KSPACE"_Packages_details.html#PKG-KSPACE, long-range Coulombic solvers, "kspace_style"_kspace_style.html, peptide, no
"LATTE"_Packages_details.html#PKG-LATTE, quantum DFTB forces via LATTE, "fix latte"_fix_latte.html, latte, ext
"MANYBODY"_Packages_details.html#PKG-MANYBODY, many-body potentials, "pair_style tersoff"_pair_tersoff.html, shear, no
"MC"_Packages_details.html#PKG-MC, Monte Carlo options, "fix gcmc"_fix_gcmc.html, n/a, no
"MESSAGE"_Packages_details.html#PKG-MESSAGE, client/server messaging, "message"_message.html, message, int
"MISC"_Packages_details.html#PKG-MISC, miscellaneous single-file commands, n/a, no, no
"MOLECULE"_Packages_details.html#PKG-MOLECULE, molecular system force fields, "Howto bioFF"_Howto_bioFF.html, peptide, no
"MPIIO"_Packages_details.html#PKG-MPIIO, MPI parallel I/O dump and restart, "dump"_dump.html, n/a, no
"MSCG"_Packages_details.html#PKG-MSCG, multi-scale coarse-graining wrapper, "fix mscg"_fix_mscg.html, mscg, ext
"OPT"_Packages_details.html#PKG-OPT, optimized pair styles, "Speed opt"_Speed_opt.html, "Benchmarks"_http://lammps.sandia.gov/bench.html, no
"PERI"_Packages_details.html#PKG-PERI, Peridynamics models, "pair_style peri"_pair_peri.html, peri, no
"POEMS"_Packages_details.html#PKG-POEMS, coupled rigid body motion, "fix poems"_fix_poems.html, rigid, int
"PYTHON"_Packages_details.html#PKG-PYTHON, embed Python code in an input script, "python"_python.html, python, sys
"QEQ"_Packages_details.html#PKG-QEQ, QEq charge equilibration, "fix qeq"_fix_qeq.html, qeq, no
"REPLICA"_Packages_details.html#PKG-REPLICA2, multi-replica methods, "Howto replica"_Howto_replica.html, tad, no
"RIGID"_Packages_details.html#PKG-RIGID, rigid bodies and constraints, "fix rigid"_fix_rigid.html, rigid, no
"SHOCK"_Packages_details.html#PKG-SHOCK, shock loading methods, "fix msst"_fix_msst.html, n/a, no
"SNAP"_Packages_details.html#PKG-SNAP, quantum-fitted potential, "pair_style snap"_pair_snap.html, snap, no
"SPIN"_Packages_details.html#PKG-SPIN, magnetic atomic spin dynamics, "Howto spins"_Howto_spins.html, SPIN, no
"SRD"_Packages_details.html#PKG-SRD, stochastic rotation dynamics, "fix srd"_fix_srd.html, srd, no
"VORONOI"_Packages_details.html#PKG-VORONOI, Voronoi tesselation, "compute voronoi/atom"_compute_voronoi_atom.html, n/a, ext :tb(ea=c,ca1=l)

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"Higher level section"_Packages.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
User packages :h3
This is a list of user packages in LAMMPS. The link for each package
name gives more details.
User packages have been contributed by users, and begin with the
"user" prefix. If a contribution is a single command (single file),
it is typically in the user-misc package. User packages don't
necessarily meet the requirements of the "standard
packages"_Packages_standard.html. This means the developers will try
to keep things working and usually can answer technical questions
about compiling the package. If you have problems using a specific
feature provided in a user package, you may need to contact the
contributor directly to get help. Information on how to submit
additions you make to LAMMPS as single files or as a standard or user
package is explained on the "Modify contribute"_Modify_contribute.html
doc page.
The "Example" column is a sub-directory in the examples directory of
the distribution which has an input script that uses the package.
E.g. "peptide" refers to the examples/peptide directory; USER/atc
refers to the examples/USER/atc directory. The "Library" column
indicates whether an extra library is needed to build and use the
package:
no = no library
sys = system library: you likely have it on your machine
int = internal library: provided with LAMMPS, but you may need to build it
ext = external library: you will need to download and install it on your machine :ul
Package, Description, Doc page, Example, Library
"USER-ADIOS"_Packages_details.html#PKG-USER-ADIOS, dump output via ADIOS, "dump adios"_dump_adios.html, USER/adios, ext
"USER-ATC"_Packages_details.html#PKG-USER-ATC, Atom-to-Continuum coupling, "fix atc"_fix_atc.html, USER/atc, int
"USER-AWPMD"_Packages_details.html#PKG-USER-AWPMD, wave packet MD, "pair_style awpmd/cut"_pair_awpmd.html, USER/awpmd, int
"USER-BOCS"_Packages_details.html#PKG-USER-BOCS, BOCS bottom up coarse graining, "fix bocs"_fix_bocs.html, USER/bocs, no
"USER-CGDNA"_Packages_details.html#PKG-USER-CGDNA, coarse-grained DNA force fields, src/USER-CGDNA/README, USER/cgdna, no
"USER-CGSDK"_Packages_details.html#PKG-USER-CGSDK, SDK coarse-graining model, "pair_style lj/sdk"_pair_sdk.html, USER/cgsdk, no
"USER-COLVARS"_Packages_details.html#PKG-USER-COLVARS, collective variables library, "fix colvars"_fix_colvars.html, USER/colvars, int
"USER-DIFFRACTION"_Packages_details.html#PKG-USER-DIFFRACTION, virtual x-ray and electron diffraction,"compute xrd"_compute_xrd.html, USER/diffraction, no
"USER-DPD"_Packages_details.html#PKG-USER-DPD, reactive dissipative particle dynamics, src/USER-DPD/README, USER/dpd, no
"USER-DRUDE"_Packages_details.html#PKG-USER-DRUDE, Drude oscillators, "Howto drude"_Howto_drude.html, USER/drude, no
"USER-EFF"_Packages_details.html#PKG-USER-EFF, electron force field,"pair_style eff/cut"_pair_eff.html, USER/eff, no
"USER-FEP"_Packages_details.html#PKG-USER-FEP, free energy perturbation,"compute fep"_compute_fep.html, USER/fep, no
"USER-H5MD"_Packages_details.html#PKG-USER-H5MD, dump output via HDF5,"dump h5md"_dump_h5md.html, n/a, ext
"USER-INTEL"_Packages_details.html#PKG-USER-INTEL, optimized Intel CPU and KNL styles,"Speed intel"_Speed_intel.html, "Benchmarks"_http://lammps.sandia.gov/bench.html, no
"USER-LB"_Packages_details.html#PKG-USER-LB, Lattice Boltzmann fluid,"fix lb/fluid"_fix_lb_fluid.html, USER/lb, no
"USER-MANIFOLD"_Packages_details.html#PKG-USER-MANIFOLD, motion on 2d surfaces,"fix manifoldforce"_fix_manifoldforce.html, USER/manifold, no
"USER-MEAMC"_Packages_details.html#PKG-USER-MEAMC, modified EAM potential (C++), "pair_style meam/c"_pair_meamc.html, meamc, no
"USER-MESO"_Packages_details.html#PKG-USER-MESO, mesoscale DPD models, "pair_style edpd"_pair_meso.html, USER/meso, no
"USER-MGPT"_Packages_details.html#PKG-USER-MGPT, fast MGPT multi-ion potentials, "pair_style mgpt"_pair_mgpt.html, USER/mgpt, no
"USER-MISC"_Packages_details.html#PKG-USER-MISC, single-file contributions, USER-MISC/README, USER/misc, no
"USER-MOFFF"_Packages_details.html#PKG-USER-MOFFF, styles for "MOF-FF"_MOFplus force field, "pair_style buck6d/coul/gauss"_pair_buck6d_coul_gauss.html, USER/mofff, no
"USER-MOLFILE"_Packages_details.html#PKG-USER-MOLFILE, "VMD"_https://www.ks.uiuc.edu/Research/vmd/ molfile plug-ins,"dump molfile"_dump_molfile.html, n/a, ext
"USER-NETCDF"_Packages_details.html#PKG-USER-NETCDF, dump output via NetCDF,"dump netcdf"_dump_netcdf.html, n/a, ext
"USER-OMP"_Packages_details.html#PKG-USER-OMP, OpenMP-enabled styles,"Speed omp"_Speed_omp.html, "Benchmarks"_http://lammps.sandia.gov/bench.html, no
"USER-PHONON"_Packages_details.html#PKG-USER-PHONON, phonon dynamical matrix,"fix phonon"_fix_phonon.html, USER/phonon, no
"USER-PLUMED"_Packages_details.html#PKG-USER-PLUMED, "PLUMED"_#PLUMED free energy library,"fix plumed"_fix_plumed.html, USER/plumed, ext
"USER-PTM"_Packages_details.html#PKG-USER-PTM, Polyhedral Template Matching,"compute ptm/atom"_compute_ptm_atom.html, n/a, no
"USER-QMMM"_Packages_details.html#PKG-USER-QMMM, QM/MM coupling,"fix qmmm"_fix_qmmm.html, USER/qmmm, ext
"USER-QTB"_Packages_details.html#PKG-USER-QTB, quantum nuclear effects,"fix qtb"_fix_qtb.html "fix qbmsst"_fix_qbmsst.html, qtb, no
"USER-QUIP"_Packages_details.html#PKG-USER-QUIP, QUIP/libatoms interface,"pair_style quip"_pair_quip.html, USER/quip, ext
"USER-REAXC"_Packages_details.html#PKG-USER-REAXC, ReaxFF potential (C/C++) ,"pair_style reaxc"_pair_reaxc.html, reax, no
"USER-SCAFACOS"_Packages_details.html#PKG-USER-SCAFACOS, wrapper on ScaFaCoS solver,"kspace_style scafacos"_kspace_style.html, USER/scafacos, ext
"USER-SDPD"_Packages_details.html#PKG-USER-SDPD, smoothed dissipative particle dynamics,"pair_style sdpd/taitwater/isothermal"_pair_sdpd_taitwater_isothermal.html, USER/sdpd, no
"USER-SMD"_Packages_details.html#PKG-USER-SMD, smoothed Mach dynamics,"SMD User Guide"_PDF/SMD_LAMMPS_userguide.pdf, USER/smd, ext
"USER-SMTBQ"_Packages_details.html#PKG-USER-SMTBQ, second moment tight binding QEq potential,"pair_style smtbq"_pair_smtbq.html, USER/smtbq, no
"USER-SPH"_Packages_details.html#PKG-USER-SPH, smoothed particle hydrodynamics,"SPH User Guide"_PDF/SPH_LAMMPS_userguide.pdf, USER/sph, no
"USER-TALLY"_Packages_details.html#PKG-USER-TALLY, pairwise tally computes,"compute XXX/tally"_compute_tally.html, USER/tally, no
"USER-UEF"_Packages_details.html#PKG-USER-UEF, extensional flow,"fix nvt/uef"_fix_nh_uef.html, USER/uef, no
"USER-VTK"_Packages_details.html#PKG-USER-VTK, dump output via VTK, "compute vtk"_dump_vtk.html, n/a, ext
"USER-YAFF"_Packages_details.html#PKG-USER-YAFF, additional styles implemented in YAFF, "angle_style cross"_angle_cross.html, USER/yaff, no :tb(ea=c,ca1=l)
:link(MOFplus,https://www.mofplus.org/content/show/MOF-FF)
:link(PLUMED,http://www.plumed.org)

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"Higher level section"_Python_head.html - "LAMMPS WWW Site"_lws -
"LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Call Python from a LAMMPS input script :h3
LAMMPS has several commands which can be used to invoke Python
code directly from an input script:
"python"_python.html
"variable python"_variable.html
"fix python/invoke"_fix_python_invoke.html
"pair_style python"_pair_python.html :ul
The "python"_python.html command which can be used to define and
execute a Python function that you write the code for. The Python
function can also be assigned to a LAMMPS python-style variable via
the "variable"_variable.html command. Each time the variable is
evaluated, either in the LAMMPS input script itself, or by another
LAMMPS command that uses the variable, this will trigger the Python
function to be invoked.
The Python code for the function can be included directly in the input
script or in an auxiliary file. The function can have arguments which
are mapped to LAMMPS variables (also defined in the input script) and
it can return a value to a LAMMPS variable. This is thus a mechanism
for your input script to pass information to a piece of Python code,
ask Python to execute the code, and return information to your input
script.
Note that a Python function can be arbitrarily complex. It can import
other Python modules, instantiate Python classes, call other Python
functions, etc. The Python code that you provide can contain more
code than the single function. It can contain other functions or
Python classes, as well as global variables or other mechanisms for
storing state between calls from LAMMPS to the function.
The Python function you provide can consist of "pure" Python code that
only performs operations provided by standard Python. However, the
Python function can also "call back" to LAMMPS through its
Python-wrapped library interface, in the manner described in the
"Python run"_Python_run.html doc page. This means it can issue LAMMPS
input script commands or query and set internal LAMMPS state. As an
example, this can be useful in an input script to create a more
complex loop with branching logic, than can be created using the
simple looping and branching logic enabled by the "next"_next.html and
"if"_if.html commands.
See the "python"_python.html doc page and the "variable"_variable.html
doc page for its python-style variables for more info, including
examples of Python code you can write for both pure Python operations
and callbacks to LAMMPS.
The "fix python/invoke"_fix_python_invoke.html command can execute
Python code at selected timesteps during a simulation run.
The "pair_style python"_pair_python.html command allows you to define
pairwise potentials as python code which encodes a single pairwise
interaction. This is useful for rapid development and debugging of a
new potential.
To use any of these commands, you only need to build LAMMPS with the
PYTHON package installed:
make yes-python
make machine :pre
Note that this will link LAMMPS with the Python library on your
system, which typically requires several auxiliary system libraries to
also be linked. The list of these libraries and the paths to find
them are specified in the lib/python/Makefile.lammps file. You need
to insure that file contains the correct information for your version
of Python and your machine to successfully build LAMMPS. See the
lib/python/README file for more info.
If you want to write Python code with callbacks to LAMMPS, then you
must also follow the steps summarized in the "Python
run"_Python_run.html doc page. I.e. you must build LAMMPS as a shared
library and insure that Python can find the python/lammps.py file and
the shared library.

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"Higher level section"_Python_head.html - "LAMMPS WWW Site"_lws -
"LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Example Python scripts that use LAMMPS :h3
These are the Python scripts included as demos in the python/examples
directory of the LAMMPS distribution, to illustrate the kinds of
things that are possible when Python wraps LAMMPS. If you create your
own scripts, send them to us and we can include them in the LAMMPS
distribution.
trivial.py, read/run a LAMMPS input script through Python,
demo.py, invoke various LAMMPS library interface routines,
simple.py, run in parallel, similar to examples/COUPLE/simple/simple.cpp,
split.py, same as simple.py but running in parallel on a subset of procs,
gui.py, GUI go/stop/temperature-slider to control LAMMPS,
plot.py, real-time temperature plot with GnuPlot via Pizza.py,
viz_tool.py, real-time viz via some viz package,
vizplotgui_tool.py, combination of viz_tool.py and plot.py and gui.py :tb(c=2)
:line
For the viz_tool.py and vizplotgui_tool.py commands, replace "tool"
with "gl" or "atomeye" or "pymol" or "vmd", depending on what
visualization package you have installed.
Note that for GL, you need to be able to run the Pizza.py GL tool,
which is included in the pizza sub-directory. See the "Pizza.py doc
pages"_pizza for more info:
:link(pizza,http://www.sandia.gov/~sjplimp/pizza.html)
Note that for AtomEye, you need version 3, and there is a line in the
scripts that specifies the path and name of the executable. See the
AtomEye WWW pages "here"_atomeye or "here"_atomeye3 for more details:
http://mt.seas.upenn.edu/Archive/Graphics/A
http://mt.seas.upenn.edu/Archive/Graphics/A3/A3.html :pre
:link(atomeye,http://mt.seas.upenn.edu/Archive/Graphics/A)
:link(atomeye3,http://mt.seas.upenn.edu/Archive/Graphics/A3/A3.html)
The latter link is to AtomEye 3 which has the scripting
capability needed by these Python scripts.
Note that for PyMol, you need to have built and installed the
open-source version of PyMol in your Python, so that you can import it
from a Python script. See the PyMol WWW pages "here"_pymolhome or
"here"_pymolopen for more details:
http://www.pymol.org
http://sourceforge.net/scm/?type=svn&group_id=4546 :pre
:link(pymolhome,http://www.pymol.org)
:link(pymolopen,http://sourceforge.net/scm/?type=svn&group_id=4546)
The latter link is to the open-source version.
Note that for VMD, you need a fairly current version (1.8.7 works for
me) and there are some lines in the pizza/vmd.py script for 4 PIZZA
variables that have to match the VMD installation on your system.
:line
See the python/README file for instructions on how to run them and the
source code for individual scripts for comments about what they do.
Here are screenshots of the vizplotgui_tool.py script in action for
different visualization package options. Click to see larger images:
:image(JPG/screenshot_gl_small.jpg,JPG/screenshot_gl.jpg)
:image(JPG/screenshot_atomeye_small.jpg,JPG/screenshot_atomeye.jpg)
:image(JPG/screenshot_pymol_small.jpg,JPG/screenshot_pymol.jpg)
:image(JPG/screenshot_vmd_small.jpg,JPG/screenshot_vmd.jpg)

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"Previous Section"_Modify.html - "LAMMPS WWW Site"_lws -
"LAMMPS Documentation"_ld - "LAMMPS Commands"_lc - "Next
Section"_Errors.html :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Use Python with LAMMPS :h2
These doc pages describe various ways that LAMMPS and Python can be
used together.
<!-- RST
.. toctree::
:maxdepth: 1
Python_overview
Python_run
Python_shlib
Python_install
Python_mpi
Python_test
Python_library
Python_pylammps
Python_examples
Python_call
END_RST -->
<!-- HTML_ONLY -->
"Overview of Python and LAMMPS"_Python_overview.html
"Run LAMMPS from Python"_Python_run.html
"Build LAMMPS as a shared library"_Python_shlib.html
"Install LAMMPS in Python"_Python_install.html
"Extend Python to run in parallel"_Python_mpi.html
"Test the Python/LAMMPS interface"_Python_test.html
"Python library interface"_Python_library.html
"PyLammps interface"_Python_pylammps.html
"Example Python scripts that use LAMMPS"_Python_examples.html
"Call Python from a LAMMPS input script"_Python_call.html :all(b)
<!-- END_HTML_ONLY -->
If you're not familiar with "Python"_http://www.python.org, it's a
powerful scripting and programming language which can do most
everything that lower-level languages like C or C++ can do in fewer
lines of code. The only drawback is slower execution speed. Python
is also easy to use as a "glue" language to drive a program through
its library interface, or to hook multiple pieces of software
together, such as a simulation code plus a visualization tool, or to
run a coupled multiscale or multiphysics model.
See the "Howto_couple"_Howto_couple.html doc page for more ideas about
coupling LAMMPS to other codes. See the "Howto
library"_Howto_library.html doc page for a description of the LAMMPS
library interface provided in src/library.h and src/library.h. That
interface is exposed to Python either when calling LAMMPS from Python
or when calling Python from a LAMMPS input script and then calling
back to LAMMPS from Python code. The library interface is designed to
be easy to add functionality to. Thus the Python interface to LAMMPS
is also easy to extend as well.
If you create interesting Python scripts that run LAMMPS or
interesting Python functions that can be called from a LAMMPS input
script, that you think would be generally useful, please post them as
a pull request to our "GitHub site"_https://github.com/lammps/lammps,
and they can be added to the LAMMPS distribution or webpage.

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"Higher level section"_Python_head.html - "LAMMPS WWW Site"_lws -
"LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Installing LAMMPS in Python :h3
For Python to invoke LAMMPS, there are 2 files it needs to know about:
python/lammps.py
liblammps.so or liblammps.dylib :ul
The python source code in lammps.py is the Python wrapper on the
LAMMPS library interface. The liblammps.so or liblammps.dylib file
is the shared LAMMPS library that Python loads dynamically.
You can achieve that Python can find these files in one of two ways:
set two environment variables pointing to the location in the source tree
run "make install-python" or run the python/install.py script explicitly :ul
When calling "make install-python" LAMMPS will try to install the
python module and the shared library into the python site-packages folders;
either the system-wide ones, or the local users ones (in case of insufficient
permissions for the global install). Python will then find the module
and shared library file automatically. The exact location of these folders
depends on your python version and your operating system.
If you set the paths to these files as environment variables, you only
have to do it once. For the csh or tcsh shells, add something like
this to your ~/.cshrc file, one line for each of the two files:
setenv PYTHONPATH $\{PYTHONPATH\}:/home/sjplimp/lammps/python
setenv LD_LIBRARY_PATH $\{LD_LIBRARY_PATH\}:/home/sjplimp/lammps/src :pre
On MacOSX you may also need to set DYLD_LIBRARY_PATH accordingly.
For Bourne/Korn shells accordingly into the corresponding files using
the "export" shell builtin.
If you use "make install-python" or the python/install.py script, you need
to invoke it every time you rebuild LAMMPS (as a shared library) or
make changes to the python/lammps.py file, so that the site-packages
files are updated with the new version.
If the default settings of "make install-python" are not what you want,
you can invoke install.py from the python directory manually as
% python install.py -m \<python module\> -l <shared library> -v <version.h file> \[-d \<pydir\>\] :pre
The -m flag points to the lammps.py python module file to be installed,
the -l flag points to the LAMMPS shared library file to be installed,
the -v flag points to the version.h file in the LAMMPS source
and the optional -d flag to a custom (legacy) installation folder :ul
If you use a legacy installation folder, you will need to set your
PYTHONPATH and LD_LIBRARY_PATH (and/or DYLD_LIBRARY_PATH) environment
variables accordingly, as described above.
Note that if you want Python to be able to load different versions of
the LAMMPS shared library (see "this section"_Python_shlib.html), you will
need to manually copy files like liblammps_g++.so into the appropriate
system directory. This is not needed if you set the LD_LIBRARY_PATH
environment variable as described above.

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"Higher level section"_Python_head.html - "LAMMPS WWW Site"_lws -
"LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Extending Python to run in parallel :h3
If you wish to run LAMMPS in parallel from Python, you need to extend
your Python with an interface to MPI. This also allows you to
make MPI calls directly from Python in your script, if you desire.
We recommend use of mpi4py:
"PyPar"_https://github.com/daleroberts/pypar :ul
As of version 2.0.0 it allows passing a custom MPI communicator to
the LAMMPS constructor, which means one can easily run one or more
LAMMPS instances on subsets of the total MPI ranks.
To install mpi4py (version mpi4py-2.0.0 as of Oct 2015), unpack it
and from its main directory, type
python setup.py build
sudo python setup.py install :pre
Again, the "sudo" is only needed if required to copy mpi4py files into
your Python distribution's site-packages directory. To install with
user privilege into the user local directory type
python setup.py install --user :pre
If you have successfully installed mpi4py, you should be able to run
Python and type
from mpi4py import MPI :pre
without error. You should also be able to run python in parallel
on a simple test script
% mpirun -np 4 python test.py :pre
where test.py contains the lines
from mpi4py import MPI
comm = MPI.COMM_WORLD
print "Proc %d out of %d procs" % (comm.Get_rank(),comm.Get_size()) :pre
and see one line of output for each processor you run on.
NOTE: To use mpi4py and LAMMPS in parallel from Python, you must
insure both are using the same version of MPI. If you only have one
MPI installed on your system, this is not an issue, but it can be if
you have multiple MPIs. Your LAMMPS build is explicit about which MPI
it is using, since you specify the details in your lo-level
src/MAKE/Makefile.foo file. Mpi4py uses the "mpicc" command to find
information about the MPI it uses to build against. And it tries to
load "libmpi.so" from the LD_LIBRARY_PATH. This may or may not find
the MPI library that LAMMPS is using. If you have problems running
both mpi4py and LAMMPS together, this is an issue you may need to
address, e.g. by moving other MPI installations so that mpi4py finds
the right one.

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"Previous Section"_Examples.html - "LAMMPS WWW Site"_lws -
"LAMMPS Documentation"_ld - "LAMMPS Commands"_lc - "Next
Section"_Tools.html :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands.html#comm)
:line
Overview of Python and LAMMPS :h3
LAMMPS can work together with Python in three ways. First, Python can
wrap LAMMPS through the its "library interface"_Howto_library.html, so
that a Python script can create one or more instances of LAMMPS and
launch one or more simulations. In Python lingo, this is called
"extending" Python with a LAMMPS module.
Second, a lower-level Python interface can be used indirectly through
the provided PyLammps and IPyLammps wrapper classes, written in Python.
These wrappers try to simplify the usage of LAMMPS in Python by
providing an object-based interface to common LAMMPS functionality.
They also reduces the amount of code necessary to parameterize LAMMPS
scripts through Python and make variables and computes directly
accessible.
Third, LAMMPS can use the Python interpreter, so that a LAMMPS
input script or styles can invoke Python code directly, and pass
information back-and-forth between the input script and Python
functions you write. This Python code can also callback to LAMMPS
to query or change its attributes through the LAMMPS Python module
mentioned above. In Python lingo, this is "embedding" Python in
LAMMPS. When used in this mode, Python can perform script operations
that the simple LAMMPS input script syntax can not.

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"Higher level section"_Python_head.html - "LAMMPS WWW Site"_lws -
"LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
PyLammps interface :h3
PyLammps is a Python wrapper class which can be created on its own or
use an existing lammps Python object. It has its own "Howto
pylammps"_Howto_pylammps.html doc page.

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"Higher level section"_Python_head.html - "LAMMPS WWW Site"_lws -
"LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Run LAMMPS from Python :h3
The LAMMPS distribution includes a python directory with all you need
to run LAMMPS from Python. The python/lammps.py file wraps the LAMMPS
library interface, with one wrapper function per LAMMPS library
function. This file makes it is possible to do the following either
from a Python script, or interactively from a Python prompt: create
one or more instances of LAMMPS, invoke LAMMPS commands or give it an
input script, run LAMMPS incrementally, extract LAMMPS results, an
modify internal LAMMPS variables. From a Python script you can do
this in serial or parallel. Running Python interactively in parallel
does not generally work, unless you have a version of Python that
extends Python to enable multiple instances of Python to read what you
type.
To do all of this, you must first build LAMMPS as a shared library,
then insure that your Python can find the python/lammps.py file and
the shared library.
Two advantages of using Python to run LAMMPS are how concise the
language is, and that it can be run interactively, enabling rapid
development and debugging. If you use it to mostly invoke costly
operations within LAMMPS, such as running a simulation for a
reasonable number of timesteps, then the overhead cost of invoking
LAMMPS through Python will be negligible.
The Python wrapper for LAMMPS uses the "ctypes" package in Python,
which auto-generates the interface code needed between Python and a
set of C-style library functions. Ctypes is part of standard Python
for versions 2.5 and later. You can check which version of Python you
have by simply typing "python" at a shell prompt.

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"Higher level section"_Python_head.html - "LAMMPS WWW Site"_lws -
"LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Build LAMMPS as a shared library :h3
Build LAMMPS as a shared library using make :h4
Instructions on how to build LAMMPS as a shared library are given on
the "Build_basics"_Build_basics.html doc page. A shared library is
one that is dynamically loadable, which is what Python requires to
wrap LAMMPS. On Linux this is a library file that ends in ".so", not
".a".
From the src directory, type
make foo mode=shlib :pre
where foo is the machine target name, such as mpi or serial.
This should create the file liblammps_foo.so in the src directory, as
well as a soft link liblammps.so, which is what the Python wrapper will
load by default. Note that if you are building multiple machine
versions of the shared library, the soft link is always set to the
most recently built version.
NOTE: If you are building LAMMPS with an MPI or FFT library or other
auxiliary libraries (used by various packages), then all of these
extra libraries must also be shared libraries. If the LAMMPS
shared-library build fails with an error complaining about this, see
the "Build_basics"_Build_basics.html doc page.
Build LAMMPS as a shared library using CMake :h4
When using CMake the following two options are necessary to generate the LAMMPS
shared library:
-D BUILD_LIB=on # enable building LAMMPS as a library
-D BUILD_SHARED_LIBS=on # enable building of LAMMPS shared library (both options are needed!) :pre
What this does is create a liblammps.so which contains the majority of LAMMPS
code. The generated lmp binary also dynamically links to this library. This
means that either this liblammps.so file has to be in the same directory, a system
library path (e.g. /usr/lib64/) or in the LD_LIBRARY_PATH.
If you want to use the shared library with Python the recommended way is to create a virtualenv and use it as
CMAKE_INSTALL_PREFIX.
# create virtualenv
virtualenv --python=$(which python3) myenv3
source myenv3/bin/activate :pre
# build library
mkdir build
cd build
cmake -D PKG_PYTHON=on -D BUILD_LIB=on -D BUILD_SHARED_LIBS=on -D CMAKE_INSTALL_PREFIX=$VIRTUAL_ENV ../cmake
make -j 4 :pre
# install into prefix
make install :pre
This will also install the Python module into your virtualenv. Since virtualenv
doesn't change your LD_LIBRARY_PATH, you still need to add its lib64 folder to
it, which contains the installed liblammps.so.
export LD_LIBRARY_PATH=$VIRTUAL_ENV/lib64:$LD_LIBRARY_PATH :pre
Starting Python outside (!) of your build directory, but with the virtualenv
enabled and with the LD_LIBRARY_PATH set gives you access to LAMMPS via Python.

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"Higher level section"_Python_head.html - "LAMMPS WWW Site"_lws -
"LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Test the Python/LAMMPS interface :h3
To test if LAMMPS is callable from Python, launch Python interactively
and type:
>>> from lammps import lammps
>>> lmp = lammps() :pre
If you get no errors, you're ready to use LAMMPS from Python. If the
2nd command fails, the most common error to see is
OSError: Could not load LAMMPS dynamic library :pre
which means Python was unable to load the LAMMPS shared library. This
typically occurs if the system can't find the LAMMPS shared library or
one of the auxiliary shared libraries it depends on, or if something
about the library is incompatible with your Python. The error message
should give you an indication of what went wrong.
You can also test the load directly in Python as follows, without
first importing from the lammps.py file:
>>> from ctypes import CDLL
>>> CDLL("liblammps.so") :pre
If an error occurs, carefully go through the steps on the
"Build_basics"_Build_basics.html doc page about building a shared
library and the "Python_install"_Python_install.html doc page about
insuring Python can find the necessary two files it needs.
[Test LAMMPS and Python in serial:] :h4
To run a LAMMPS test in serial, type these lines into Python
interactively from the bench directory:
>>> from lammps import lammps
>>> lmp = lammps()
>>> lmp.file("in.lj") :pre
Or put the same lines in the file test.py and run it as
% python test.py :pre
Either way, you should see the results of running the in.lj benchmark
on a single processor appear on the screen, the same as if you had
typed something like:
lmp_g++ -in in.lj :pre
[Test LAMMPS and Python in parallel:] :h4
To run LAMMPS in parallel, assuming you have installed the
"PyPar"_https://github.com/daleroberts/pypar package as discussed
above, create a test.py file containing these lines:
import pypar
from lammps import lammps
lmp = lammps()
lmp.file("in.lj")
print "Proc %d out of %d procs has" % (pypar.rank(),pypar.size()),lmp
pypar.finalize() :pre
To run LAMMPS in parallel, assuming you have installed the
"mpi4py"_https://bitbucket.org/mpi4py/mpi4py package as discussed
above, create a test.py file containing these lines:
from mpi4py import MPI
from lammps import lammps
lmp = lammps()
lmp.file("in.lj")
me = MPI.COMM_WORLD.Get_rank()
nprocs = MPI.COMM_WORLD.Get_size()
print "Proc %d out of %d procs has" % (me,nprocs),lmp
MPI.Finalize() :pre
You can either script in parallel as:
% mpirun -np 4 python test.py :pre
and you should see the same output as if you had typed
% mpirun -np 4 lmp_g++ -in in.lj :pre
Note that if you leave out the 3 lines from test.py that specify PyPar
commands you will instantiate and run LAMMPS independently on each of
the P processors specified in the mpirun command. In this case you
should get 4 sets of output, each showing that a LAMMPS run was made
on a single processor, instead of one set of output showing that
LAMMPS ran on 4 processors. If the 1-processor outputs occur, it
means that PyPar is not working correctly.
Also note that once you import the PyPar module, PyPar initializes MPI
for you, and you can use MPI calls directly in your Python script, as
described in the PyPar documentation. The last line of your Python
script should be pypar.finalize(), to insure MPI is shut down
correctly.
[Running Python scripts:] :h4
Note that any Python script (not just for LAMMPS) can be invoked in
one of several ways:
% python foo.script
% python -i foo.script
% foo.script :pre
The last command requires that the first line of the script be
something like this:
#!/usr/local/bin/python
#!/usr/local/bin/python -i :pre
where the path points to where you have Python installed, and that you
have made the script file executable:
% chmod +x foo.script :pre
Without the "-i" flag, Python will exit when the script finishes.
With the "-i" flag, you will be left in the Python interpreter when
the script finishes, so you can type subsequent commands. As
mentioned above, you can only run Python interactively when running
Python on a single processor, not in parallel.

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"Higher level section"_Run_head.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Basics of running LAMMPS :h3
LAMMPS is run from the command line, reading commands from a
file via the -in command line flag, or from standard input.
Using the "-in in.file" variant is recommended:
lmp_serial < in.file
lmp_serial -in in.file
/path/to/lammps/src/lmp_serial < in.file
mpirun -np 4 lmp_mpi -in in.file
mpirun -np 8 /path/to//lammps/src/lmp_mpi -in in.file
mpirun -np 6 /usr/local/bin/lmp -in in.file :pre
You normally run the LAMMPS command in the directory where your
input script is located. That is also where output files are
produced by default, unless you provide specific other paths in
your input script or on the command line. As in some of the
examples above, the LAMMPS executable itself can be placed elsewhere.
NOTE: The redirection operator "<" will not always work when running
in parallel with mpirun; for those systems the -in form is required.
As LAMMPS runs it prints info to the screen and a logfile named
log.lammps. More info about output is given on the "Run
output"_Run_output.html doc page.
If LAMMPS encounters errors in the input script or while running a
simulation it will print an ERROR message and stop or a WARNING
message and continue. See the "Errors"_Errors.html doc page for a
discussion of the various kinds of errors LAMMPS can or can't detect,
a list of all ERROR and WARNING messages, and what to do about them.
:line
LAMMPS can run the same problem on any number of processors, including
a single processor. In theory you should get identical answers on any
number of processors and on any machine. In practice, numerical
round-off can cause slight differences and eventual divergence of
molecular dynamics phase space trajectories. See the "Errors
common"_Errors_common.html doc page for discussion of this.
LAMMPS can run as large a problem as will fit in the physical memory
of one or more processors. If you run out of memory, you must run on
more processors or define a smaller problem.
If you run LAMMPS in parallel via mpirun, you should be aware of the
"processors"_processors.html command which controls how MPI tasks are
mapped to the simulation box, as well as mpirun options that control
how MPI tasks are assigned to physical cores of the node(s) of the
machine you are running on. These settings can improve performance,
though the defaults are often adequate.
For example, it is often important to bind MPI tasks (processes) to
physical cores (processor affinity), so that the operating system does
not migrate them during a simulation. If this is not the default
behavior on your machine, the mpirun option "--bind-to core" (OpenMPI)
or "-bind-to core" (MPICH) can be used.
If the LAMMPS command(s) you are using support multi-threading, you
can set the number of threads per MPI task via the environment
variable OMP_NUM_THREADS, before you launch LAMMPS:
export OMP_NUM_THREADS=2 # bash
setenv OMP_NUM_THREADS 2 # csh or tcsh :pre
This can also be done via the "package"_package.html command or via
the "-pk command-line switch"_Run_options.html which invokes the
package command. See the "package"_package.html command or
"Speed"_Speed.html doc pages for more details about which accelerator
packages and which commands support multi-threading.
:line
You can experiment with running LAMMPS using any of the input scripts
provided in the examples or bench directory. Input scripts are named
in.* and sample outputs are named log.*.P where P is the number of
processors it was run on.
Some of the examples or benchmarks require LAMMPS to be built with
optional packages.

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"Previous Section"_Build.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc - "Next
Section"_Commands.html :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Run LAMMPS :h2
These pages explain how to run LAMMPS once you have "installed an
executable"_Install.html or "downloaded the source code"_Install.html
and "built an executable"_Build.html. The "Commands"_Commands.html
doc page describes how input scripts are structured and the commands
they can contain.
<!-- RST
.. toctree::
:maxdepth: 1
Run_basics
Run_options
Run_output
Run_windows
END_RST -->
<!-- HTML_ONLY -->
"Basics of running LAMMPS"_Run_basics.html
"Command-line options"_Run_options.html
"Screen and logfile output"_Run_output.html
"Running LAMMPS on Windows"_Run_windows.html :all(b)
<!-- END_HTML_ONLY -->

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"Higher level section"_Run_head.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Command-line options :h3
At run time, LAMMPS recognizes several optional command-line switches
which may be used in any order. Either the full word or a one-or-two
letter abbreviation can be used:
"-e or -echo"_#echo
"-h or -help"_#help
"-i or -in"_#file
"-k or -kokkos"_#run-kokkos
"-l or -log"_#log
"-m or -mpicolor"_#mpicolor
"-nc or -nocite"_#nocite
"-pk or -package"_#package
"-p or -partition"_#partition
"-pl or -plog"_#plog
"-ps or -pscreen"_#pscreen
"-ro or -reorder"_#reorder
"-r2data or -restart2data"_#restart2data
"-r2dump or -restart2dump"_#restart2dump
"-sc or -screen"_#screen
"-sf or -suffix"_#suffix
"-v or -var"_#var :ul
For example, the lmp_mpi executable might be launched as follows:
mpirun -np 16 lmp_mpi -v f tmp.out -l my.log -sc none -i in.alloy
mpirun -np 16 lmp_mpi -var f tmp.out -log my.log -screen none -in in.alloy :pre
:line
[-echo style] :link(echo)
Set the style of command echoing. The style can be {none} or {screen}
or {log} or {both}. Depending on the style, each command read from
the input script will be echoed to the screen and/or logfile. This
can be useful to figure out which line of your script is causing an
input error. The default value is {log}. The echo style can also be
set by using the "echo"_echo.html command in the input script itself.
:line
[-help] :link(help)
Print a brief help summary and a list of options compiled into this
executable for each LAMMPS style (atom_style, fix, compute,
pair_style, bond_style, etc). This can tell you if the command you
want to use was included via the appropriate package at compile time.
LAMMPS will print the info and immediately exit if this switch is
used.
:line
[-in file] :link(file)
Specify a file to use as an input script. This is an optional switch
when running LAMMPS in one-partition mode. If it is not specified,
LAMMPS reads its script from standard input, typically from a script
via I/O redirection; e.g. lmp_linux < in.run. I/O redirection should
also work in parallel, but if it does not (in the unlikely case that
an MPI implementation does not support it), then use the -in flag.
Note that this is a required switch when running LAMMPS in
multi-partition mode, since multiple processors cannot all read from
stdin.
:line
[-kokkos on/off keyword/value ...] :link(run-kokkos)
Explicitly enable or disable KOKKOS support, as provided by the KOKKOS
package. Even if LAMMPS is built with this package, as described
in "Speed kokkos"_Speed_kokkos.html, this switch must be set to enable
running with KOKKOS-enabled styles the package provides. If the
switch is not set (the default), LAMMPS will operate as if the KOKKOS
package were not installed; i.e. you can run standard LAMMPS or with
the GPU or USER-OMP packages, for testing or benchmarking purposes.
Additional optional keyword/value pairs can be specified which
determine how Kokkos will use the underlying hardware on your
platform. These settings apply to each MPI task you launch via the
"mpirun" or "mpiexec" command. You may choose to run one or more MPI
tasks per physical node. Note that if you are running on a desktop
machine, you typically have one physical node. On a cluster or
supercomputer there may be dozens or 1000s of physical nodes.
Either the full word or an abbreviation can be used for the keywords.
Note that the keywords do not use a leading minus sign. I.e. the
keyword is "t", not "-t". Also note that each of the keywords has a
default setting. Examples of when to use these options and what
settings to use on different platforms is given on the "Speed
kokkos"_Speed_kokkos.html doc page.
d or device
g or gpus
t or threads
n or numa :ul
device Nd :pre
This option is only relevant if you built LAMMPS with CUDA=yes, you
have more than one GPU per node, and if you are running with only one
MPI task per node. The Nd setting is the ID of the GPU on the node to
run on. By default Nd = 0. If you have multiple GPUs per node, they
have consecutive IDs numbered as 0,1,2,etc. This setting allows you
to launch multiple independent jobs on the node, each with a single
MPI task per node, and assign each job to run on a different GPU.
gpus Ng Ns :pre
This option is only relevant if you built LAMMPS with CUDA=yes, you
have more than one GPU per node, and you are running with multiple MPI
tasks per node (up to one per GPU). The Ng setting is how many GPUs
you will use. The Ns setting is optional. If set, it is the ID of a
GPU to skip when assigning MPI tasks to GPUs. This may be useful if
your desktop system reserves one GPU to drive the screen and the rest
are intended for computational work like running LAMMPS. By default
Ng = 1 and Ns is not set.
Depending on which flavor of MPI you are running, LAMMPS will look for
one of these 4 environment variables
SLURM_LOCALID (various MPI variants compiled with SLURM support)
MPT_LRANK (HPE MPI)
MV2_COMM_WORLD_LOCAL_RANK (Mvapich)
OMPI_COMM_WORLD_LOCAL_RANK (OpenMPI) :pre
which are initialized by the "srun", "mpirun" or "mpiexec" commands.
The environment variable setting for each MPI rank is used to assign a
unique GPU ID to the MPI task.
threads Nt :pre
This option assigns Nt number of threads to each MPI task for
performing work when Kokkos is executing in OpenMP or pthreads mode.
The default is Nt = 1, which essentially runs in MPI-only mode. If
there are Np MPI tasks per physical node, you generally want Np*Nt =
the number of physical cores per node, to use your available hardware
optimally. This also sets the number of threads used by the host when
LAMMPS is compiled with CUDA=yes.
numa Nm :pre
This option is only relevant when using pthreads with hwloc support.
In this case Nm defines the number of NUMA regions (typically sockets)
on a node which will be utilized by a single MPI rank. By default Nm
= 1. If this option is used the total number of worker-threads per
MPI rank is threads*numa. Currently it is always almost better to
assign at least one MPI rank per NUMA region, and leave numa set to
its default value of 1. This is because letting a single process span
multiple NUMA regions induces a significant amount of cross NUMA data
traffic which is slow.
:line
[-log file] :link(log)
Specify a log file for LAMMPS to write status information to. In
one-partition mode, if the switch is not used, LAMMPS writes to the
file log.lammps. If this switch is used, LAMMPS writes to the
specified file. In multi-partition mode, if the switch is not used, a
log.lammps file is created with hi-level status information. Each
partition also writes to a log.lammps.N file where N is the partition
ID. If the switch is specified in multi-partition mode, the hi-level
logfile is named "file" and each partition also logs information to a
file.N. For both one-partition and multi-partition mode, if the
specified file is "none", then no log files are created. Using a
"log"_log.html command in the input script will override this setting.
Option -plog will override the name of the partition log files file.N.
:line
[-mpicolor] color :link(mpicolor)
If used, this must be the first command-line argument after the LAMMPS
executable name. It is only used when LAMMPS is launched by an mpirun
command which also launches another executable(s) at the same time.
(The other executable could be LAMMPS as well.) The color is an
integer value which should be different for each executable (another
application may set this value in a different way). LAMMPS and the
other executable(s) perform an MPI_Comm_split() with their own colors
to shrink the MPI_COMM_WORLD communication to be the subset of
processors they are actually running on.
Currently, this is only used in LAMMPS to perform client/server
messaging with another application. LAMMPS can act as either a client
or server (or both). More details are given on the "Howto
client/server"_Howto_client_server.html doc page.
Specifically, this refers to the "mpi/one" mode of messaging provided
by the "message"_message.html command and the CSlib library LAMMPS
links with from the lib/message directory. See the
"message"_message.html command for more details.
:line
[-nocite] :link(nocite)
Disable writing the log.cite file which is normally written to list
references for specific cite-able features used during a LAMMPS run.
See the "citation page"_http://lammps.sandia.gov/cite.html for more
details.
:line
[-package style args ....] :link(package)
Invoke the "package"_package.html command with style and args. The
syntax is the same as if the command appeared at the top of the input
script. For example "-package gpu 2" or "-pk gpu 2" is the same as
"package gpu 2"_package.html in the input script. The possible styles
and args are documented on the "package"_package.html doc page. This
switch can be used multiple times, e.g. to set options for the
USER-INTEL and USER-OMP packages which can be used together.
Along with the "-suffix" command-line switch, this is a convenient
mechanism for invoking accelerator packages and their options without
having to edit an input script.
:line
[-partition 8x2 4 5 ...] :link(partition)
Invoke LAMMPS in multi-partition mode. When LAMMPS is run on P
processors and this switch is not used, LAMMPS runs in one partition,
i.e. all P processors run a single simulation. If this switch is
used, the P processors are split into separate partitions and each
partition runs its own simulation. The arguments to the switch
specify the number of processors in each partition. Arguments of the
form MxN mean M partitions, each with N processors. Arguments of the
form N mean a single partition with N processors. The sum of
processors in all partitions must equal P. Thus the command
"-partition 8x2 4 5" has 10 partitions and runs on a total of 25
processors.
Running with multiple partitions can be useful for running
"multi-replica simulations"_Howto_replica.html, where each replica
runs on one or a few processors. Note that with MPI installed on a
machine (e.g. your desktop), you can run on more (virtual) processors
than you have physical processors.
To run multiple independent simulations from one input script, using
multiple partitions, see the "Howto multiple"_Howto_multiple.html doc
page. World- and universe-style "variables"_variable.html are useful
in this context.
:line
[-plog file] :link(plog)
Specify the base name for the partition log files, so partition N
writes log information to file.N. If file is none, then no partition
log files are created. This overrides the filename specified in the
-log command-line option. This option is useful when working with
large numbers of partitions, allowing the partition log files to be
suppressed (-plog none) or placed in a sub-directory (-plog
replica_files/log.lammps) If this option is not used the log file for
partition N is log.lammps.N or whatever is specified by the -log
command-line option.
:line
[-pscreen file] :link(pscreen)
Specify the base name for the partition screen file, so partition N
writes screen information to file.N. If file is none, then no
partition screen files are created. This overrides the filename
specified in the -screen command-line option. This option is useful
when working with large numbers of partitions, allowing the partition
screen files to be suppressed (-pscreen none) or placed in a
sub-directory (-pscreen replica_files/screen). If this option is not
used the screen file for partition N is screen.N or whatever is
specified by the -screen command-line option.
:line
[-reorder] :link(reorder)
This option has 2 forms:
-reorder nth N
-reorder custom filename :pre
Reorder the processors in the MPI communicator used to instantiate
LAMMPS, in one of several ways. The original MPI communicator ranks
all P processors from 0 to P-1. The mapping of these ranks to
physical processors is done by MPI before LAMMPS begins. It may be
useful in some cases to alter the rank order. E.g. to insure that
cores within each node are ranked in a desired order. Or when using
the "run_style verlet/split"_run_style.html command with 2 partitions
to insure that a specific Kspace processor (in the 2nd partition) is
matched up with a specific set of processors in the 1st partition.
See the "Speed tips"_Speed_tips.html doc page for more details.
If the keyword {nth} is used with a setting {N}, then it means every
Nth processor will be moved to the end of the ranking. This is useful
when using the "run_style verlet/split"_run_style.html command with 2
partitions via the -partition command-line switch. The first set of
processors will be in the first partition, the 2nd set in the 2nd
partition. The -reorder command-line switch can alter this so that
the 1st N procs in the 1st partition and one proc in the 2nd partition
will be ordered consecutively, e.g. as the cores on one physical node.
This can boost performance. For example, if you use "-reorder nth 4"
and "-partition 9 3" and you are running on 12 processors, the
processors will be reordered from
0 1 2 3 4 5 6 7 8 9 10 11 :pre
to
0 1 2 4 5 6 8 9 10 3 7 11 :pre
so that the processors in each partition will be
0 1 2 4 5 6 8 9 10
3 7 11 :pre
See the "processors" command for how to insure processors from each
partition could then be grouped optimally for quad-core nodes.
If the keyword is {custom}, then a file that specifies a permutation
of the processor ranks is also specified. The format of the reorder
file is as follows. Any number of initial blank or comment lines
(starting with a "#" character) can be present. These should be
followed by P lines of the form:
I J :pre
where P is the number of processors LAMMPS was launched with. Note
that if running in multi-partition mode (see the -partition switch
above) P is the total number of processors in all partitions. The I
and J values describe a permutation of the P processors. Every I and
J should be values from 0 to P-1 inclusive. In the set of P I values,
every proc ID should appear exactly once. Ditto for the set of P J
values. A single I,J pairing means that the physical processor with
rank I in the original MPI communicator will have rank J in the
reordered communicator.
Note that rank ordering can also be specified by many MPI
implementations, either by environment variables that specify how to
order physical processors, or by config files that specify what
physical processors to assign to each MPI rank. The -reorder switch
simply gives you a portable way to do this without relying on MPI
itself. See the "processors out"_processors.html command for how
to output info on the final assignment of physical processors to
the LAMMPS simulation domain.
:line
[-restart2data restartfile \[remap\] datafile keyword value ...]
:link(restart2data)
Convert the restart file into a data file and immediately exit. This
is the same operation as if the following 2-line input script were
run:
read_restart restartfile \[remap\]
write_data datafile keyword value ... :pre
The specified restartfile and/or datafile name may contain the wild-card
character "*". The restartfile name may also contain the wild-card
character "%". The meaning of these characters is explained on the
"read_restart"_read_restart.html and "write_data"_write_data.html doc
pages. The use of "%" means that a parallel restart file can be read.
Note that a filename such as file.* may need to be enclosed in quotes or
the "*" character prefixed with a backslash ("\") to avoid shell
expansion of the "*" character.
Following restartfile argument, the optional word "remap" may be used.
This has the same effect like adding it to a
"read_restart"_read_restart.html command, and operates as explained on
its doc page. This is useful if reading the restart file triggers an
error that atoms have been lost. In that case, use of the remap flag
should allow the data file to still be produced.
The syntax following restartfile (or remap), namely
datafile keyword value ... :pre
is identical to the arguments of the "write_data"_write_data.html
command. See its doc page for details. This includes its
optional keyword/value settings.
:line
[-restart2dump restartfile \[remap\] group-ID dumpstyle dumpfile arg1 arg2 ...] :link(restart2dump)
Convert the restart file into a dump file and immediately exit. This
is the same operation as if the following 2-line input script were
run:
read_restart restartfile \[remap\]
write_dump group-ID dumpstyle dumpfile arg1 arg2 ... :pre
Note that the specified restartfile and dumpfile names may contain
wild-card characters ("*","%") as explained on the
"read_restart"_read_restart.html and "write_dump"_write_dump.html doc
pages. The use of "%" means that a parallel restart file and/or
parallel dump file can be read and/or written. Note that a filename
such as file.* may need to be enclosed in quotes or the "*" character
prefixed with a backslash ("\") to avoid shell expansion of the "*"
character.
Note that following the restartfile argument, the optional word "remap"
can be used. This has the effect as adding it to the
"read_restart"_read_restart.html command, as explained on its doc page.
This is useful if reading the restart file triggers an error that atoms
have been lost. In that case, use of the remap flag should allow the
dump file to still be produced.
The syntax following restartfile (or remap), namely
group-ID dumpstyle dumpfile arg1 arg2 ... :pre
is identical to the arguments of the "write_dump"_write_dump.html
command. See its doc page for details. This includes what per-atom
fields are written to the dump file and optional dump_modify settings,
including ones that affect how parallel dump files are written, e.g.
the {nfile} and {fileper} keywords. See the
"dump_modify"_dump_modify.html doc page for details.
:line
[-screen file] :link(screen)
Specify a file for LAMMPS to write its screen information to. In
one-partition mode, if the switch is not used, LAMMPS writes to the
screen. If this switch is used, LAMMPS writes to the specified file
instead and you will see no screen output. In multi-partition mode,
if the switch is not used, hi-level status information is written to
the screen. Each partition also writes to a screen.N file where N is
the partition ID. If the switch is specified in multi-partition mode,
the hi-level screen dump is named "file" and each partition also
writes screen information to a file.N. For both one-partition and
multi-partition mode, if the specified file is "none", then no screen
output is performed. Option -pscreen will override the name of the
partition screen files file.N.
:line
[-suffix style args] :link(suffix)
Use variants of various styles if they exist. The specified style can
be {gpu}, {intel}, {kk}, {omp}, {opt}, or {hybrid}. These
refer to optional packages that LAMMPS can be built with, as described
in "Accelerate performance"_Speed.html. The "gpu" style corresponds to the
GPU package, the "intel" style to the USER-INTEL package, the "kk"
style to the KOKKOS package, the "opt" style to the OPT package, and
the "omp" style to the USER-OMP package. The hybrid style is the only
style that accepts arguments. It allows for two packages to be
specified. The first package specified is the default and will be used
if it is available. If no style is available for the first package,
the style for the second package will be used if available. For
example, "-suffix hybrid intel omp" will use styles from the
USER-INTEL package if they are installed and available, but styles for
the USER-OMP package otherwise.
Along with the "-package" command-line switch, this is a convenient
mechanism for invoking accelerator packages and their options without
having to edit an input script.
As an example, all of the packages provide a "pair_style
lj/cut"_pair_lj.html variant, with style names lj/cut/gpu,
lj/cut/intel, lj/cut/kk, lj/cut/omp, and lj/cut/opt. A variant style
can be specified explicitly in your input script, e.g. pair_style
lj/cut/gpu. If the -suffix switch is used the specified suffix
(gpu,intel,kk,omp,opt) is automatically appended whenever your input
script command creates a new "atom"_atom_style.html,
"pair"_pair_style.html, "fix"_fix.html, "compute"_compute.html, or
"run"_run_style.html style. If the variant version does not exist,
the standard version is created.
For the GPU package, using this command-line switch also invokes the
default GPU settings, as if the command "package gpu 1" were used at
the top of your input script. These settings can be changed by using
the "-package gpu" command-line switch or the "package
gpu"_package.html command in your script.
For the USER-INTEL package, using this command-line switch also
invokes the default USER-INTEL settings, as if the command "package
intel 1" were used at the top of your input script. These settings
can be changed by using the "-package intel" command-line switch or
the "package intel"_package.html command in your script. If the
USER-OMP package is also installed, the hybrid style with "intel omp"
arguments can be used to make the omp suffix a second choice, if a
requested style is not available in the USER-INTEL package. It will
also invoke the default USER-OMP settings, as if the command "package
omp 0" were used at the top of your input script. These settings can
be changed by using the "-package omp" command-line switch or the
"package omp"_package.html command in your script.
For the KOKKOS package, using this command-line switch also invokes
the default KOKKOS settings, as if the command "package kokkos" were
used at the top of your input script. These settings can be changed
by using the "-package kokkos" command-line switch or the "package
kokkos"_package.html command in your script.
For the OMP package, using this command-line switch also invokes the
default OMP settings, as if the command "package omp 0" were used at
the top of your input script. These settings can be changed by using
the "-package omp" command-line switch or the "package
omp"_package.html command in your script.
The "suffix"_suffix.html command can also be used within an input
script to set a suffix, or to turn off or back on any suffix setting
made via the command line.
:line
[-var name value1 value2 ...] :link(var)
Specify a variable that will be defined for substitution purposes when
the input script is read. This switch can be used multiple times to
define multiple variables. "Name" is the variable name which can be a
single character (referenced as $x in the input script) or a full
string (referenced as $\{abc\}). An "index-style
variable"_variable.html will be created and populated with the
subsequent values, e.g. a set of filenames. Using this command-line
option is equivalent to putting the line "variable name index value1
value2 ..." at the beginning of the input script. Defining an index
variable as a command-line argument overrides any setting for the same
index variable in the input script, since index variables cannot be
re-defined.
See the "variable"_variable.html command for more info on defining
index and other kinds of variables and the "Commands
parse"_Commands_parse.html page for more info on using variables in
input scripts.
NOTE: Currently, the command-line parser looks for arguments that
start with "-" to indicate new switches. Thus you cannot specify
multiple variable values if any of them start with a "-", e.g. a
negative numeric value. It is OK if the first value1 starts with a
"-", since it is automatically skipped.

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"Higher level section"_Run_head.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Screen and logfile output :h3
As LAMMPS reads an input script, it prints information to both the
screen and a log file about significant actions it takes to setup a
simulation. When the simulation is ready to begin, LAMMPS performs
various initializations, and prints info about the run it is about to
perform, including the amount of memory (in MBytes per processor) that
the simulation requires. It also prints details of the initial
thermodynamic state of the system. During the run itself,
thermodynamic information is printed periodically, every few
timesteps. When the run concludes, LAMMPS prints the final
thermodynamic state and a total run time for the simulation. It also
appends statistics about the CPU time and storage requirements for the
simulation. An example set of statistics is shown here:
Loop time of 2.81192 on 4 procs for 300 steps with 2004 atoms :pre
Performance: 18.436 ns/day 1.302 hours/ns 106.689 timesteps/s
97.0% CPU use with 4 MPI tasks x no OpenMP threads :pre
MPI task timings breakdown:
Section | min time | avg time | max time |%varavg| %total
---------------------------------------------------------------
Pair | 1.9808 | 2.0134 | 2.0318 | 1.4 | 71.60
Bond | 0.0021894 | 0.0060319 | 0.010058 | 4.7 | 0.21
Kspace | 0.3207 | 0.3366 | 0.36616 | 3.1 | 11.97
Neigh | 0.28411 | 0.28464 | 0.28516 | 0.1 | 10.12
Comm | 0.075732 | 0.077018 | 0.07883 | 0.4 | 2.74
Output | 0.00030518 | 0.00042665 | 0.00078821 | 1.0 | 0.02
Modify | 0.086606 | 0.086631 | 0.086668 | 0.0 | 3.08
Other | | 0.007178 | | | 0.26 :pre
Nlocal: 501 ave 508 max 490 min
Histogram: 1 0 0 0 0 0 1 1 0 1
Nghost: 6586.25 ave 6628 max 6548 min
Histogram: 1 0 1 0 0 0 1 0 0 1
Neighs: 177007 ave 180562 max 170212 min
Histogram: 1 0 0 0 0 0 0 1 1 1 :pre
Total # of neighbors = 708028
Ave neighs/atom = 353.307
Ave special neighs/atom = 2.34032
Neighbor list builds = 26
Dangerous builds = 0 :pre
:line
The first section provides a global loop timing summary. The {loop
time} is the total wall-clock time for the simulation to run. The
{Performance} line is provided for convenience to help predict how
long it will take to run a desired physical simulation. The {CPU use}
line provides the CPU utilization per MPI task; it should be close to
100% times the number of OpenMP threads (or 1 of not using OpenMP).
Lower numbers correspond to delays due to file I/O or insufficient
thread utilization.
:line
The {MPI task} section gives the breakdown of the CPU run time (in
seconds) into major categories:
{Pair} = non-bonded force computations
{Bond} = bonded interactions: bonds, angles, dihedrals, impropers
{Kspace} = long-range interactions: Ewald, PPPM, MSM
{Neigh} = neighbor list construction
{Comm} = inter-processor communication of atoms and their properties
{Output} = output of thermodynamic info and dump files
{Modify} = fixes and computes invoked by fixes
{Other} = all the remaining time :ul
For each category, there is a breakdown of the least, average and most
amount of wall time any processor spent on this category of
computation. The "%varavg" is the percentage by which the max or min
varies from the average. This is an indication of load imbalance. A
percentage close to 0 is perfect load balance. A large percentage is
imbalance. The final "%total" column is the percentage of the total
loop time is spent in this category.
When using the "timer full"_timer.html setting, an additional column
is added that also prints the CPU utilization in percent. In addition,
when using {timer full} and the "package omp"_package.html command are
active, a similar timing summary of time spent in threaded regions to
monitor thread utilization and load balance is provided. A new {Thread
timings} section is also added, which lists the time spent in reducing
the per-thread data elements to the storage for non-threaded
computation. These thread timings are measured for the first MPI rank
only and thus, because the breakdown for MPI tasks can change from
MPI rank to MPI rank, this breakdown can be very different for
individual ranks. Here is an example output for this section:
Thread timings breakdown (MPI rank 0):
Total threaded time 0.6846 / 90.6%
Section | min time | avg time | max time |%varavg| %total
---------------------------------------------------------------
Pair | 0.5127 | 0.5147 | 0.5167 | 0.3 | 75.18
Bond | 0.0043139 | 0.0046779 | 0.0050418 | 0.5 | 0.68
Kspace | 0.070572 | 0.074541 | 0.07851 | 1.5 | 10.89
Neigh | 0.084778 | 0.086969 | 0.089161 | 0.7 | 12.70
Reduce | 0.0036485 | 0.003737 | 0.0038254 | 0.1 | 0.55 :pre
:line
The third section above lists the number of owned atoms (Nlocal),
ghost atoms (Nghost), and pair-wise neighbors stored per processor.
The max and min values give the spread of these values across
processors with a 10-bin histogram showing the distribution. The total
number of histogram counts is equal to the number of processors.
:line
The last section gives aggregate statistics (across all processors)
for pair-wise neighbors and special neighbors that LAMMPS keeps track
of (see the "special_bonds"_special_bonds.html command). The number
of times neighbor lists were rebuilt is tallied, as is the number of
potentially {dangerous} rebuilds. If atom movement triggered neighbor
list rebuilding (see the "neigh_modify"_neigh_modify.html command),
then dangerous reneighborings are those that were triggered on the
first timestep atom movement was checked for. If this count is
non-zero you may wish to reduce the delay factor to insure no force
interactions are missed by atoms moving beyond the neighbor skin
distance before a rebuild takes place.
:line
If an energy minimization was performed via the
"minimize"_minimize.html command, additional information is printed,
e.g.
Minimization stats:
Stopping criterion = linesearch alpha is zero
Energy initial, next-to-last, final =
-6372.3765206 -8328.46998942 -8328.46998942
Force two-norm initial, final = 1059.36 5.36874
Force max component initial, final = 58.6026 1.46872
Final line search alpha, max atom move = 2.7842e-10 4.0892e-10
Iterations, force evaluations = 701 1516 :pre
The first line prints the criterion that determined minimization was
converged. The next line lists the initial and final energy, as well
as the energy on the next-to-last iteration. The next 2 lines give a
measure of the gradient of the energy (force on all atoms). The
2-norm is the "length" of this 3N-component force vector; the largest
component (x, y, or z) of force (infinity-norm) is also given. Then
information is provided about the line search and statistics on how
many iterations and force-evaluations the minimizer required.
Multiple force evaluations are typically done at each iteration to
perform a 1d line minimization in the search direction. See the
"minimize"_minimize.html doc page for more details.
:line
If a "kspace_style"_kspace_style.html long-range Coulombics solver
that performs FFTs was used during the run (PPPM, Ewald), then
additional information is printed, e.g.
FFT time (% of Kspce) = 0.200313 (8.34477)
FFT Gflps 3d 1d-only = 2.31074 9.19989 :pre
The first line is the time spent doing 3d FFTs (several per timestep)
and the fraction it represents of the total KSpace time (listed
above). Each 3d FFT requires computation (3 sets of 1d FFTs) and
communication (transposes). The total flops performed is 5Nlog_2(N),
where N is the number of points in the 3d grid. The FFTs are timed
with and without the communication and a Gflop rate is computed. The
3d rate is with communication; the 1d rate is without (just the 1d
FFTs). Thus you can estimate what fraction of your FFT time was spent
in communication, roughly 75% in the example above.

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"Higher level section"_Run_head.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Running LAMMPS on Windows :h3
To run a serial (non-MPI) executable, follow these steps:
Get a command prompt by going to Start->Run... ,
then typing "cmd". :ulb,l
Move to the directory where you have your input script,
(e.g. by typing: cd "Documents"). :l
At the command prompt, type "lmp_serial -in in.file", where
in.file is the name of your LAMMPS input script. :l,ule
Note that the serial executable includes support for multi-threading
parallelization from the styles in the USER-OMP packages. To run with
4 threads, you can type this:
lmp_serial -in in.lj -pk omp 4 -sf omp :pre
:line
For the MPI executable, which allows you to run LAMMPS under Windows
in parallel, follow these steps.
Download and install a compatible MPI library binary package:
for 32-bit Windows: "mpich2-1.4.1p1-win-ia32.msi"_http://download.lammps.org/thirdparty/mpich2-1.4.1p1-win-ia32.msi
for 64-bit Windows: "mpich2-1.4.1p1-win-x86-64.msi"_http://download.lammps.org/thirdparty/mpich2-1.4.1p1-win-x86-64.msi :ul
The LAMMPS Windows installer packages will automatically adjust your
path for the default location of this MPI package. After the
installation of the MPICH2 software, it needs to be integrated into
the system. For this you need to start a Command Prompt in
{Administrator Mode} (right click on the icon and select it). Change
into the MPICH2 installation directory, then into the sub-directory
[bin] and execute [smpd.exe -install]. Exit the command window.
Get a new, regular command prompt by going to Start->Run... ,
then typing "cmd". :ulb,l
Move to the directory where you have your input file
(e.g. by typing: cd "Documents"). :l,ule
Then type something like this:
mpiexec -localonly 4 lmp_mpi -in in.file
mpiexec -np 4 lmp_mpi -in in.file :pre
where in.file is the name of your LAMMPS input script. For the latter
case, you may be prompted to enter your password.
In this mode, output may not immediately show up on the screen, so if
your input script takes a long time to execute, you may need to be
patient before the output shows up.
The parallel executable can also run on a single processor by typing
something like this:
lmp_mpi -in in.lj :pre
Note that the parallel executable also includes OpenMP
multi-threading, which can be combined with MPI using something like:
mpiexec -localonly 2 lmp_mpi -in in.lj -pk omp 2 -sf omp :pre

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"Previous Section"_Package.html - "LAMMPS WWW Site"_lws -
"LAMMPS Documentation"_ld - "LAMMPS Commands"_lc - "Next
Section"_Howto.html :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Accelerate performance :h2
This section describes various methods for improving LAMMPS
performance for different classes of problems running on different
kinds of machines.
There are two thrusts to the discussion that follows. The first is
using code options that implement alternate algorithms that can
speed-up a simulation. The second is to use one of the several
accelerator packages provided with LAMMPS that contain code optimized
for certain kinds of hardware, including multi-core CPUs, GPUs, and
Intel Xeon Phi co-processors.
The "Benchmark page"_http://lammps.sandia.gov/bench.html of the LAMMPS
web site gives performance results for the various accelerator
packages discussed on the "Speed packages"_Speed_packages.html doc
page, for several of the standard LAMMPS benchmark problems, as a
function of problem size and number of compute nodes, on different
hardware platforms.
<!-- RST
.. toctree::
:maxdepth: 1
Speed_bench
Speed_measure
Speed_tips
Speed_packages
Speed_compare
END_RST -->
<!-- HTML_ONLY -->
"Benchmarks"_Speed_bench.html
"Measuring performance"_Speed_measure.html
"General tips"_Speed_tips.html
"Accelerator packages"_Speed_packages.html
"GPU package"_Speed_gpu.html
"USER-INTEL package"_Speed_intel.html
"KOKKOS package"_Speed_kokkos.html
"USER-OMP package"_Speed_omp.html
"OPT package"_Speed_opt.html
"Comparison of accelerator packages"_Speed_compare.html :all(b)
<!-- END_HTML_ONLY -->

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"Higher level section"_Speed.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Benchmarks :h3
Current LAMMPS performance is discussed on the "Benchmarks
page"_http://lammps.sandia.gov/bench.html of the "LAMMPS website"_lws
where timings and parallel efficiency are listed. The page has
several sections, which are briefly described below:
CPU performance on 5 standard problems, strong and weak scaling
GPU and Xeon Phi performance on same and related problems
Comparison of cost of interatomic potentials
Performance of huge, billion-atom problems :ul
The 5 standard problems are as follow:
LJ = atomic fluid, Lennard-Jones potential with 2.5 sigma cutoff (55
neighbors per atom), NVE integration :olb,l
Chain = bead-spring polymer melt of 100-mer chains, FENE bonds and LJ
pairwise interactions with a 2^(1/6) sigma cutoff (5 neighbors per
atom), NVE integration :l
EAM = metallic solid, Cu EAM potential with 4.95 Angstrom cutoff (45
neighbors per atom), NVE integration :l
Chute = granular chute flow, frictional history potential with 1.1
sigma cutoff (7 neighbors per atom), NVE integration :l
Rhodo = rhodopsin protein in solvated lipid bilayer, CHARMM force
field with a 10 Angstrom LJ cutoff (440 neighbors per atom),
particle-particle particle-mesh (PPPM) for long-range Coulombics, NPT
integration :l
:ole
Input files for these 5 problems are provided in the bench directory
of the LAMMPS distribution. Each has 32,000 atoms and runs for 100
timesteps. The size of the problem (number of atoms) can be varied
using command-line switches as described in the bench/README file.
This is an easy way to test performance and either strong or weak
scalability on your machine.
The bench directory includes a few log.* files that show performance
of these 5 problems on 1 or 4 cores of Linux desktop. The bench/FERMI
and bench/KEPLER dirs have input files and scripts and instructions
for running the same (or similar) problems using OpenMP or GPU or Xeon
Phi acceleration options. See the README files in those dirs and the
"Speed packages"_Speed_packages.html doc pages for instructions on how
to build LAMMPS and run on that kind of hardware.
The bench/POTENTIALS directory has input files which correspond to the
table of results on the
"Potentials"_http://lammps.sandia.gov/bench.html#potentials section of
the Benchmarks web page. So you can also run those test problems on
your machine.
The "billion-atom"_http://lammps.sandia.gov/bench.html#billion section
of the Benchmarks web page has performance data for very large
benchmark runs of simple Lennard-Jones (LJ) models, which use the
bench/in.lj input script.
:line
For all the benchmarks, a useful metric is the CPU cost per atom per
timestep. Since performance scales roughly linearly with problem size
and timesteps for all LAMMPS models (i.e. interatomic or coarse-grained
potentials), the run time of any problem using the same model (atom
style, force field, cutoff, etc) can then be estimated.
Performance on a parallel machine can also be predicted from one-core
or one-node timings if the parallel efficiency can be estimated. The
communication bandwidth and latency of a particular parallel machine
affects the efficiency. On most machines LAMMPS will give a parallel
efficiency on these benchmarks above 50% so long as the number of
atoms/core is a few 100 or greater, and closer to 100% for large
numbers of atoms/core. This is for all-MPI mode with one MPI task per
core. For nodes with accelerator options or hardware (OpenMP, GPU,
Phi), you should first measure single node performance. Then you can
estimate parallel performance for multi-node runs using the same logic
as for all-MPI mode, except that now you will typically need many more
atoms/node to achieve good scalability.

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"Higher level section"_Speed.html - "LAMMPS WWW Site"_lws - "LAMMPS
Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)
:line
Comparison of various accelerator packages :h3
The next section compares and contrasts the various accelerator
options, since there are multiple ways to perform OpenMP threading,
run on GPUs, optimize for vector units on CPUs and run on Intel
Xeon Phi (co-)processors.
All of these packages can accelerate a LAMMPS calculation taking
advantage of hardware features, but they do it in different ways
and acceleration is not always guaranteed.
As a consequence, for a particular simulation on specific hardware,
one package may be faster than the other. We give some guidelines
below, but the best way to determine which package is faster for your
input script is to try multiple of them on your machine and experiment
with available performance tuning settings. See the benchmarking
section below for examples where this has been done.
[Guidelines for using each package optimally:]
Both, the GPU and the KOKKOS package allows you to assign multiple
MPI ranks (= CPU cores) to the same GPU. For the GPU package, this
can lead to a speedup through better utilization of the GPU (by
overlapping computation and data transfer) and more efficient
computation of the non-GPU accelerated parts of LAMMPS through MPI
parallelization, as all system data is maintained and updated on
the host. For KOKKOS, there is less to no benefit from this, due
to its different memory management model, which tries to retain
data on the GPU.
:ulb,l
The GPU package moves per-atom data (coordinates, forces, and
(optionally) neighbor list data, if not computed on the GPU) between
the CPU and GPU at every timestep. The KOKKOS/CUDA package only does
this on timesteps when a CPU calculation is required (e.g. to invoke
a fix or compute that is non-GPU-ized). Hence, if you can formulate
your input script to only use GPU-ized fixes and computes, and avoid
doing I/O too often (thermo output, dump file snapshots, restart files),
then the data transfer cost of the KOKKOS/CUDA package can be very low,
causing it to run faster than the GPU package. :l
The GPU package is often faster than the KOKKOS/CUDA package, when the
number of atoms per GPU is on the smaller side. The crossover point,
in terms of atoms/GPU at which the KOKKOS/CUDA package becomes faster
depends strongly on the pair style. For example, for a simple Lennard Jones
system the crossover (in single precision) is often about 50K-100K
atoms per GPU. When performing double precision calculations the
crossover point can be significantly smaller. :l
Both KOKKOS and GPU package compute bonded interactions (bonds, angles,
etc) on the CPU. If the GPU package is running with several MPI processes
assigned to one GPU, the cost of computing the bonded interactions is
spread across more CPUs and hence the GPU package can run faster in these
cases. :l
When using LAMMPS with multiple MPI ranks assigned to the same GPU, its
performance depends to some extent on the available bandwidth between
the CPUs and the GPU. This can differ significantly based on the
available bus technology, capability of the host CPU and mainboard,
the wiring of the buses and whether switches are used to increase the
number of available bus slots, or if GPUs are housed in an external
enclosure. This can become quite complex. :l
To achieve significant acceleration through GPUs, both KOKKOS and GPU
package require capable GPUs with fast on-device memory and efficient
data transfer rates. This requests capable upper mid-level to high-end
(desktop) GPUs. Using lower performance GPUs (e.g. on laptops) may
result in a slowdown instead. :l
For the GPU package, specifically when running in parallel with MPI,
if it often more efficient to exclude the PPPM kspace style from GPU
acceleration and instead run it - concurrently with a GPU accelerated
pair style - on the CPU. This can often be easily achieved with placing
a {suffix off} command before and a {suffix on} command after the
{kspace_style pppm} command. :l
The KOKKOS/OpenMP and USER-OMP package have different thread management
strategies, which should result in USER-OMP being more efficient for a
small number of threads with increasing overhead as the number of threads
per MPI rank grows. The KOKKOS/OpenMP kernels have less overhead in that
case, but have lower performance with few threads. :l
The USER-INTEL package contains many options and settings for achieving
additional performance on Intel hardware (CPU and accelerator cards), but
to unlock this potential, an Intel compiler is required. The package code
will compile with GNU gcc, but it will not be as efficient. :l
:ule
[Differences between the GPU and KOKKOS packages:]
The GPU package accelerates only pair force, neighbor list, and (parts
of) PPPM calculations. The KOKKOS package attempts to run most of the
calculation on the GPU, but can transparently support non-accelerated
code (with a performance penalty due to having data transfers between
host and GPU). :ulb,l
The GPU package requires neighbor lists to be built on the CPU when using
exclusion lists, or a triclinic simulation box. :l
The GPU package can be compiled for CUDA or OpenCL and thus supports
both, Nvidia and AMD GPUs well. On Nvidia hardware, using CUDA is typically
resulting in equal or better performance over OpenCL. :l
OpenCL in the GPU package does theoretically also support Intel CPUs or
Intel Xeon Phi, but the native support for those in KOKKOS (or USER-INTEL)
is superior. :l
:ule

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