2006-09-22 00:22:34 +08:00
2015-07-30 22:53:28 +08:00
<!DOCTYPE html>
<!-- [if IE 8]><html class="no - js lt - ie9" lang="en" > <![endif] -->
<!-- [if gt IE 8]><! --> < html class = "no-js" lang = "en" > <!-- <![endif] -->
< head >
< meta charset = "utf-8" >
< meta name = "viewport" content = "width=device-width, initial-scale=1.0" >
2015-12-21 23:20:41 +08:00
< title > fix addforce command — LAMMPS documentation< / title >
2015-07-30 22:53:28 +08:00
2006-09-22 00:22:34 +08:00
2015-07-30 22:53:28 +08:00
2006-09-22 00:22:34 +08:00
2015-07-30 22:53:28 +08:00
2006-09-22 00:22:34 +08:00
2015-07-30 22:53:28 +08:00
2006-09-22 00:22:34 +08:00
2015-07-30 22:53:28 +08:00
2006-09-22 00:22:34 +08:00
2015-07-30 22:53:28 +08:00
< link rel = "stylesheet" href = "_static/css/theme.css" type = "text/css" / >
2009-08-09 06:03:37 +08:00
2015-07-30 22:53:28 +08:00
< link rel = "stylesheet" href = "_static/sphinxcontrib-images/LightBox2/lightbox2/css/lightbox.css" type = "text/css" / >
2009-08-09 06:03:37 +08:00
2015-07-30 22:53:28 +08:00
2015-12-21 23:20:41 +08:00
< link rel = "top" title = "LAMMPS documentation" href = "index.html" / >
2009-08-09 06:03:37 +08:00
2015-07-30 22:53:28 +08:00
< script src = "_static/js/modernizr.min.js" > < / script >
2009-08-09 06:03:37 +08:00
2015-07-30 22:53:28 +08:00
< / head >
2009-08-09 06:03:37 +08:00
2015-07-30 22:53:28 +08:00
< body class = "wy-body-for-nav" role = "document" >
< div class = "wy-grid-for-nav" >
< nav data-toggle = "wy-nav-shift" class = "wy-nav-side" >
< div class = "wy-side-nav-search" >
< a href = "Manual.html" class = "icon icon-home" > LAMMPS
< / a >
< div role = "search" >
< form id = "rtd-search-form" class = "wy-form" action = "search.html" method = "get" >
< input type = "text" name = "q" placeholder = "Search docs" / >
< input type = "hidden" name = "check_keywords" value = "yes" / >
< input type = "hidden" name = "area" value = "default" / >
< / form >
< / div >
< / div >
< div class = "wy-menu wy-menu-vertical" data-spy = "affix" role = "navigation" aria-label = "main navigation" >
< ul >
< li class = "toctree-l1" > < a class = "reference internal" href = "Section_intro.html" > 1. Introduction< / a > < / li >
< li class = "toctree-l1" > < a class = "reference internal" href = "Section_start.html" > 2. Getting Started< / a > < / li >
< li class = "toctree-l1" > < a class = "reference internal" href = "Section_commands.html" > 3. Commands< / a > < / li >
< li class = "toctree-l1" > < a class = "reference internal" href = "Section_packages.html" > 4. Packages< / a > < / li >
< li class = "toctree-l1" > < a class = "reference internal" href = "Section_accelerate.html" > 5. Accelerating LAMMPS performance< / a > < / li >
< li class = "toctree-l1" > < a class = "reference internal" href = "Section_howto.html" > 6. How-to discussions< / a > < / li >
< li class = "toctree-l1" > < a class = "reference internal" href = "Section_example.html" > 7. Example problems< / a > < / li >
< li class = "toctree-l1" > < a class = "reference internal" href = "Section_perf.html" > 8. Performance & scalability< / a > < / li >
< li class = "toctree-l1" > < a class = "reference internal" href = "Section_tools.html" > 9. Additional tools< / a > < / li >
< li class = "toctree-l1" > < a class = "reference internal" href = "Section_modify.html" > 10. Modifying & extending LAMMPS< / a > < / li >
< li class = "toctree-l1" > < a class = "reference internal" href = "Section_python.html" > 11. Python interface to LAMMPS< / a > < / li >
< li class = "toctree-l1" > < a class = "reference internal" href = "Section_errors.html" > 12. Errors< / a > < / li >
< li class = "toctree-l1" > < a class = "reference internal" href = "Section_history.html" > 13. Future and history< / a > < / li >
< / ul >
< / div >
< / nav >
< section data-toggle = "wy-nav-shift" class = "wy-nav-content-wrap" >
< nav class = "wy-nav-top" role = "navigation" aria-label = "top navigation" >
< i data-toggle = "wy-nav-top" class = "fa fa-bars" > < / i >
< a href = "Manual.html" > LAMMPS< / a >
< / nav >
< div class = "wy-nav-content" >
< div class = "rst-content" >
< div role = "navigation" aria-label = "breadcrumbs navigation" >
< ul class = "wy-breadcrumbs" >
< li > < a href = "Manual.html" > Docs< / a > » < / li >
< li > fix addforce command< / li >
< li class = "wy-breadcrumbs-aside" >
< a href = "http://lammps.sandia.gov" > Website< / a >
< a href = "Section_commands.html#comm" > Commands< / a >
< / li >
< / ul >
< hr / >
< / div >
< div role = "main" class = "document" itemscope = "itemscope" itemtype = "http://schema.org/Article" >
< div itemprop = "articleBody" >
< div class = "section" id = "fix-addforce-command" >
< span id = "index-0" > < / span > < h1 > fix addforce command< a class = "headerlink" href = "#fix-addforce-command" title = "Permalink to this headline" > ¶< / a > < / h1 >
< / div >
< div class = "section" id = "fix-addforce-cuda-command" >
< h1 > fix addforce/cuda command< a class = "headerlink" href = "#fix-addforce-cuda-command" title = "Permalink to this headline" > ¶< / a > < / h1 >
< div class = "section" id = "syntax" >
< h2 > Syntax< a class = "headerlink" href = "#syntax" title = "Permalink to this headline" > ¶< / a > < / h2 >
< div class = "highlight-python" > < div class = "highlight" > < pre > fix ID group-ID addforce fx fy fz keyword value ...
< / pre > < / div >
< / div >
< ul class = "simple" >
< li > ID, group-ID are documented in < a class = "reference internal" href = "fix.html" > < em > fix< / em > < / a > command< / li >
< li > addforce = style name of this fix command< / li >
< li > fx,fy,fz = force component values (force units)< / li >
< / ul >
< div class = "highlight-python" > < div class = "highlight" > < pre > any of fx,fy,fz can be a variable (see below)
< / pre > < / div >
< / div >
< ul class = "simple" >
< li > zero or more keyword/value pairs may be appended to args< / li >
< li > keyword = < em > every< / em > or < em > region< / em > or < em > energy< / em > < / li >
< / ul >
< pre class = "literal-block" >
< em > every< / em > value = Nevery
2015-07-31 00:49:30 +08:00
Nevery = add force every this many timesteps
< em > region< / em > value = region-ID
region-ID = ID of region atoms must be in to have added force
< em > energy< / em > value = v_name
v_name = variable with name that calculates the potential energy of each atom in the added force field
2015-07-30 22:53:28 +08:00
< / pre >
< / div >
< div class = "section" id = "examples" >
< h2 > Examples< a class = "headerlink" href = "#examples" title = "Permalink to this headline" > ¶< / a > < / h2 >
< div class = "highlight-python" > < div class = "highlight" > < pre > fix kick flow addforce 1.0 0.0 0.0
2010-04-23 22:24:18 +08:00
fix kick flow addforce 1.0 0.0 v_oscillate
2015-07-30 22:53:28 +08:00
fix ff boundary addforce 0.0 0.0 v_push energy v_espace
< / pre > < / div >
< / div >
< / div >
< div class = "section" id = "description" >
< h2 > Description< a class = "headerlink" href = "#description" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > Add fx,fy,fz to the corresponding component of force for each atom in
2006-09-22 00:22:34 +08:00
the group. This command can be used to give an additional push to
atoms in a simulation, such as for a simulation of Poiseuille flow in
2015-07-30 22:53:28 +08:00
a channel.< / p >
< p > Any of the 3 quantities defining the force components can be specified
as an equal-style or atom-style < a class = "reference internal" href = "variable.html" > < em > variable< / em > < / a > , namely < em > fx< / em > ,
< em > fy< / em > , < em > fz< / em > . If the value is a variable, it should be specified as
2010-08-13 07:10:38 +08:00
v_name, where name is the variable name. In this case, the variable
2013-01-09 04:26:00 +08:00
will be evaluated each timestep, and its value(s) used to determine
2015-07-30 22:53:28 +08:00
the force component.< / p >
< p > Equal-style variables can specify formulas with various mathematical
functions, and include < a class = "reference internal" href = "thermo_style.html" > < em > thermo_style< / em > < / a > command
2010-04-23 22:24:18 +08:00
keywords for the simulation box parameters and timestep and elapsed
2015-07-30 22:53:28 +08:00
time. Thus it is easy to specify a time-dependent force field.< / p >
< p > Atom-style variables can specify the same formulas as equal-style
2010-04-23 22:24:18 +08:00
variables but can also include per-atom values, such as atom
coordinates. Thus it is easy to specify a spatially-dependent force
2015-07-30 22:53:28 +08:00
field with optional time-dependence as well.< / p >
< p > If the < em > every< / em > keyword is used, the < em > Nevery< / em > setting determines how
2014-09-06 00:58:30 +08:00
often the forces are applied. The default value is 1, for every
2015-07-30 22:53:28 +08:00
timestep.< / p >
< p > If the < em > region< / em > keyword is used, the atom must also be in the
specified geometric < a class = "reference internal" href = "region.html" > < em > region< / em > < / a > in order to have force added
to it.< / p >
< hr class = "docutils" / >
< p > Adding a force to atoms implies a change in their potential energy as
they move due to the applied force field. For dynamics via the “ run”
command, this energy can be optionally added to the system’ s potential
2010-04-23 22:24:18 +08:00
energy for thermodynamic output (see below). For energy minimization
2015-07-30 22:53:28 +08:00
via the “ minimize” command, this energy must be added to the system’ s
2010-04-23 22:24:18 +08:00
potential energy to formulate a self-consistent minimization problem
2015-07-30 22:53:28 +08:00
(see below).< / p >
< p > The < em > energy< / em > keyword is not allowed if the added force is a constant
2010-04-23 22:24:18 +08:00
vector F = (fx,fy,fz), with all components defined as numeric
constants and not as variables. This is because LAMMPS can compute
the energy for each atom directly as E = -x dot F = -(x*fx + y*fy +
2015-07-30 22:53:28 +08:00
z*fz), so that -Grad(E) = F.< / p >
< p > The < em > energy< / em > keyword is optional if the added force is defined with
2010-04-23 22:24:18 +08:00
one or more variables, and if you are performing dynamics via the
2015-07-30 22:53:28 +08:00
< a class = "reference internal" href = "run.html" > < em > run< / em > < / a > command. If the keyword is not used, LAMMPS will set
the energy to 0.0, which is typically fine for dynamics.< / p >
< p > The < em > energy< / em > keyword is required if the added force is defined with
2010-04-23 22:24:18 +08:00
one or more variables, and you are performing energy minimization via
2015-07-30 22:53:28 +08:00
the “ minimize” command. The keyword specifies the name of an
atom-style < a class = "reference internal" href = "variable.html" > < em > variable< / em > < / a > which is used to compute the
2010-08-13 07:10:38 +08:00
energy of each atom as function of its position. Like variables used
2015-07-30 22:53:28 +08:00
for < em > fx< / em > , < em > fy< / em > , < em > fz< / em > , the energy variable is specified as v_name,
where name is the variable name.< / p >
< p > Note that when the < em > energy< / em > keyword is used during an energy
2010-04-23 22:24:18 +08:00
minimization, you must insure that the formula defined for the
2015-07-30 22:53:28 +08:00
atom-style < a class = "reference internal" href = "variable.html" > < em > variable< / em > < / a > is consistent with the force
2010-04-23 22:25:37 +08:00
variable formulas, i.e. that -Grad(E) = F. For example, if the force
were a spring-like F = kx, then the energy formula should be E =
2015-07-30 22:53:28 +08:00
-0.5kx^2. If you don’ t do this correctly, the minimization will not
converge properly.< / p >
< hr class = "docutils" / >
< p > Styles with a < em > cuda< / em > suffix are functionally the same as the
2011-06-09 05:46:03 +08:00
corresponding style without the suffix. They have been optimized to
run faster, depending on your available hardware, as discussed in
2015-07-30 22:53:28 +08:00
< a class = "reference internal" href = "Section_accelerate.html" > < em > Section_accelerate< / em > < / a > of the manual. The
2011-12-14 04:35:35 +08:00
accelerated styles take the same arguments and should produce the same
2015-07-30 22:53:28 +08:00
results, except for round-off and precision issues.< / p >
< p > These accelerated styles are part of the USER-CUDA package. They are
only enabled if LAMMPS was built with that package. See the < a class = "reference internal" href = "Section_start.html#start-3" > < span > Making LAMMPS< / span > < / a > section for more info.< / p >
< p > You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the < a class = "reference internal" href = "Section_start.html#start-7" > < span > -suffix command-line switch< / span > < / a > when you invoke LAMMPS, or you can
use the < a class = "reference internal" href = "suffix.html" > < em > suffix< / em > < / a > command in your input script.< / p >
< p > See < a class = "reference internal" href = "Section_accelerate.html" > < em > Section_accelerate< / em > < / a > of the manual for
more instructions on how to use the accelerated styles effectively.< / p >
< / div >
< hr class = "docutils" / >
< div class = "section" id = "restart-fix-modify-output-run-start-stop-minimize-info" >
< h2 > Restart, fix_modify, output, run start/stop, minimize info< a class = "headerlink" href = "#restart-fix-modify-output-run-start-stop-minimize-info" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > No information about this fix is written to < a class = "reference internal" href = "restart.html" > < em > binary restart files< / em > < / a > .< / p >
< p > The < a class = "reference internal" href = "fix_modify.html" > < em > fix_modify< / em > < / a > < em > energy< / em > option is supported by this
fix to add the potential “ energy” inferred by the added force to the
system’ s potential energy as part of < a class = "reference internal" href = "thermo_style.html" > < em > thermodynamic output< / em > < / a > . This is a fictitious quantity but is
needed so that the < a class = "reference internal" href = "minimize.html" > < em > minimize< / em > < / a > command can include the
2008-08-01 23:10:00 +08:00
forces added by this fix in a consistent manner. I.e. there is a
decrease in potential energy when atoms move in the direction of the
2015-07-30 22:53:28 +08:00
added force.< / p >
< p > This fix computes a global scalar and a global 3-vector of forces,
which can be accessed by various < a class = "reference internal" href = "Section_howto.html#howto-15" > < span > output commands< / span > < / a > . The scalar is the potential
2011-08-26 01:01:01 +08:00
energy discussed above. The vector is the total force on the group of
atoms before the forces on individual atoms are changed by the fix.
2015-07-30 22:53:28 +08:00
The scalar and vector values calculated by this fix are “ extensive” .< / p >
< p > No parameter of this fix can be used with the < em > start/stop< / em > keywords of
the < a class = "reference internal" href = "run.html" > < em > run< / em > < / a > command.< / p >
< p > The forces due to this fix are imposed during an energy minimization,
invoked by the < a class = "reference internal" href = "minimize.html" > < em > minimize< / em > < / a > command. You should not
2010-04-23 22:24:18 +08:00
specify force components with a variable that has time-dependence for
use with a minimizer, since the minimizer increments the timestep as
2015-07-30 22:53:28 +08:00
the iteration count during the minimization.< / p >
2015-12-11 01:23:56 +08:00
< div class = "admonition note" >
< p class = "first admonition-title" > Note< / p >
< p class = "last" > If you want the fictitious potential energy associated with the
added forces to be included in the total potential energy of the
system (the quantity being minimized), you MUST enable the
2015-07-30 22:53:28 +08:00
< a class = "reference internal" href = "fix_modify.html" > < em > fix_modify< / em > < / a > < em > energy< / em > option for this fix.< / p >
< / div >
< / div >
< div class = "section" id = "restrictions" >
< h2 > Restrictions< a class = "headerlink" href = "#restrictions" title = "Permalink to this headline" > ¶< / a > < / h2 >
< blockquote >
< div > none< / div > < / blockquote >
< / div >
< div class = "section" id = "related-commands" >
< h2 > Related commands< a class = "headerlink" href = "#related-commands" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > < a class = "reference internal" href = "fix_setforce.html" > < em > fix setforce< / em > < / a > , < a class = "reference internal" href = "fix_aveforce.html" > < em > fix aveforce< / em > < / a > < / p >
< / div >
< div class = "section" id = "default" >
< h2 > Default< a class = "headerlink" href = "#default" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > The option default for the every keyword is every = 1.< / p >
< / div >
< / div >
< / div >
< / div >
< footer >
< hr / >
< div role = "contentinfo" >
< p >
2015-12-11 01:23:56 +08:00
© Copyright 2013 Sandia Corporation.
2015-07-30 22:53:28 +08:00
< / p >
< / div >
Built with < a href = "http://sphinx-doc.org/" > Sphinx< / a > using a < a href = "https://github.com/snide/sphinx_rtd_theme" > theme< / a > provided by < a href = "https://readthedocs.org" > Read the Docs< / a > .
< / footer >
< / div >
< / div >
< / section >
< / div >
< script type = "text/javascript" >
var DOCUMENTATION_OPTIONS = {
URL_ROOT:'./',
2015-12-21 23:20:41 +08:00
VERSION:'',
2015-07-30 22:53:28 +08:00
COLLAPSE_INDEX:false,
FILE_SUFFIX:'.html',
HAS_SOURCE: true
};
< / script >
< script type = "text/javascript" src = "_static/jquery.js" > < / script >
< script type = "text/javascript" src = "_static/underscore.js" > < / script >
< script type = "text/javascript" src = "_static/doctools.js" > < / script >
< script type = "text/javascript" src = "https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML" > < / script >
< script type = "text/javascript" src = "_static/sphinxcontrib-images/LightBox2/lightbox2/js/jquery-1.11.0.min.js" > < / script >
< script type = "text/javascript" src = "_static/sphinxcontrib-images/LightBox2/lightbox2/js/lightbox.min.js" > < / script >
< script type = "text/javascript" src = "_static/sphinxcontrib-images/LightBox2/lightbox2-customize/jquery-noconflict.js" > < / script >
< script type = "text/javascript" src = "_static/js/theme.js" > < / script >
< script type = "text/javascript" >
jQuery(function () {
SphinxRtdTheme.StickyNav.enable();
});
< / script >
< / body >
< / html >
