forked from lijiext/lammps
118 lines
3.8 KiB
Plaintext
118 lines
3.8 KiB
Plaintext
.. index:: compute pe
|
|
|
|
compute pe command
|
|
==================
|
|
|
|
compute pe/cuda command
|
|
=======================
|
|
|
|
Syntax
|
|
""""""
|
|
|
|
.. parsed-literal::
|
|
|
|
compute ID group-ID pe keyword ...
|
|
|
|
* ID, group-ID are documented in :doc:`compute <compute>` command
|
|
* pe = style name of this compute command
|
|
* zero or more keywords may be appended
|
|
* keyword = *pair* or *bond* or *angle* or *dihedral* or *improper* or *kspace*
|
|
|
|
Examples
|
|
""""""""
|
|
|
|
.. parsed-literal::
|
|
|
|
compute 1 all pe
|
|
compute molPE all pe bond angle dihedral improper
|
|
|
|
Description
|
|
"""""""""""
|
|
|
|
Define a computation that calculates the potential energy of the
|
|
entire system of atoms. The specified group must be "all". See the
|
|
:doc:`compute pe/atom <compute_pe_atom>` command if you want per-atom
|
|
energies. These per-atom values could be summed for a group of atoms
|
|
via the :doc:`compute reduce <compute_reduce>` command.
|
|
|
|
The energy is calculated by the various pair, bond, etc potentials
|
|
defined for the simulation. If no extra keywords are listed, then the
|
|
potential energy is the sum of pair, bond, angle, dihedral, improper,
|
|
and kspace (long-range) energy. If any extra keywords are listed,
|
|
then only those components are summed to compute the potential energy.
|
|
|
|
The Kspace contribution requires 1 extra FFT each timestep the energy
|
|
is calculated, if using the PPPM solver via the :doc:`kspace_style pppm <kspace_style>` command. Thus it can increase the cost of the
|
|
PPPM calculation if it is needed on a large fraction of the simulation
|
|
timesteps.
|
|
|
|
Various fixes can contribute to the total potential energy of the
|
|
system. See the doc pages for :doc:`individual fixes <fix>` for
|
|
details. The *thermo* option of the
|
|
:doc:`compute_modify <compute_modify>` command determines whether these
|
|
contributions are added into the computed potential energy. If no
|
|
keywords are specified the default is *yes*. If any keywords are
|
|
specified, the default is *no*.
|
|
|
|
A compute of this style with the ID of "thermo_pe" is created when
|
|
LAMMPS starts up, as if this command were in the input script:
|
|
|
|
.. parsed-literal::
|
|
|
|
compute thermo_pe all pe
|
|
|
|
See the "thermo_style" command for more details.
|
|
|
|
|
|
----------
|
|
|
|
|
|
Styles with a *cuda*, *gpu*, *intel*, *kk*, *omp*, or *opt* suffix are
|
|
functionally the same as the corresponding style without the suffix.
|
|
They have been optimized to run faster, depending on your available
|
|
hardware, as discussed in :doc:`Section_accelerate <Section_accelerate>`
|
|
of the manual. The accelerated styles take the same arguments and
|
|
should produce the same results, except for round-off and precision
|
|
issues.
|
|
|
|
These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
|
|
KOKKOS, USER-OMP and OPT packages, respectively. They are only
|
|
enabled if LAMMPS was built with those packages. See the :ref:`Making LAMMPS <start_3>` section for more info.
|
|
|
|
You can specify the accelerated styles explicitly in your input script
|
|
by including their suffix, or you can use the :ref:`-suffix command-line switch <start_7>` when you invoke LAMMPS, or you can
|
|
use the :doc:`suffix <suffix>` command in your input script.
|
|
|
|
See :doc:`Section_accelerate <Section_accelerate>` of the manual for
|
|
more instructions on how to use the accelerated styles effectively.
|
|
|
|
|
|
----------
|
|
|
|
|
|
**Output info:**
|
|
|
|
This compute calculates a global scalar (the potential energy). This
|
|
value can be used by any command that uses a global scalar value from
|
|
a compute as input. See :ref:`Section_howto 15 <howto_15>` for an overview of LAMMPS output
|
|
options.
|
|
|
|
The scalar value calculated by this compute is "extensive". The
|
|
scalar value will be in energy :doc:`units <units>`.
|
|
|
|
Restrictions
|
|
""""""""""""
|
|
none
|
|
|
|
Related commands
|
|
""""""""""""""""
|
|
|
|
:doc:`compute pe/atom <compute_pe_atom>`
|
|
|
|
**Default:** none
|
|
|
|
|
|
.. _lws: http://lammps.sandia.gov
|
|
.. _ld: Manual.html
|
|
.. _lc: Section_commands.html#comm
|