Homec4science
Diffusion lammps (lammps-icms) Browse

lammps/doc/html/fix_ti_rs.html
b013a4096541lammps-icms

Last Change
Raw File

fix_ti_rs.html
View Options

<!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">
<title>fix ti/rs command &mdash; LAMMPS documentation</title>
<link rel="stylesheet" href="_static/css/theme.css" type="text/css" />
<link rel="stylesheet" href="_static/sphinxcontrib-images/LightBox2/lightbox2/css/lightbox.css" type="text/css" />
<link rel="top" title="LAMMPS documentation" href="index.html"/>
<script src="_static/js/modernizr.min.js"></script>
</head>
<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 &amp; 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 &amp; 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>
&nbsp;
</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> &raquo;</li>
<li>fix ti/rs 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-ti-rs-command">
<span id="index-0"></span><h1>fix ti/rs command</h1>
<div class="section" id="syntax">
<h2>Syntax</h2>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">fix</span> <span class="n">ID</span> <span class="n">group</span><span class="o">-</span><span class="n">ID</span> <span class="n">ti</span><span class="o">/</span><span class="n">rs</span> <span class="n">lambda_initial</span> <span class="n">lambda_final</span> <span class="n">t_switch</span> <span class="n">t_equil</span> <span class="n">keyword</span> <span class="n">value</span> <span class="o">...</span>
</pre></div>
</div>
<ul class="simple">
<li>ID, group-ID are documented in <a class="reference internal" href="fix.html"><span class="doc">fix</span></a> command</li>
<li>ti/rs = style name of this fix command</li>
<li>lambda_initial/lambda_final = initial/final values of the coupling parameter</li>
<li>t_switch/t_equil = number of steps of the switching/equilibration procedure</li>
<li>keyword = <em>function</em></li>
</ul>
<pre class="literal-block">
<em>function</em> value = function-ID
function-ID = ID of the switching function (1, 2 or 3)
</pre>
<p><strong>Example:</strong></p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">fix</span> <span class="n">ref</span> <span class="nb">all</span> <span class="n">ti</span><span class="o">/</span><span class="n">rs</span> <span class="mf">50.0</span> <span class="mi">2000</span> <span class="mi">1000</span>
<span class="n">fix</span> <span class="n">vf</span> <span class="n">vacancy</span> <span class="n">ti</span><span class="o">/</span><span class="n">rs</span> <span class="mf">10.0</span> <span class="mi">70000</span> <span class="mi">50000</span> <span class="n">function</span> <span class="mi">2</span>
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>This fix allows you to compute the free energy temperature dependence
by performing a thermodynamic integration procedure known as
Reversible Scaling <a class="reference internal" href="#dekoning99"><span class="std std-ref">(de Koning99,</span></a> <a class="reference internal" href="#dekoning00a"><span class="std std-ref">de Koning00a)</span></a>. The thermodynamic integration is performed
using the nonequilibrium method of Adiabatic Switching
<a class="reference internal" href="fix_ti_spring.html#watanabe"><span class="std std-ref">(Watanabe,</span></a> <a class="reference internal" href="fix_ti_spring.html#dekoning96"><span class="std std-ref">de Koning96)</span></a>.</p>
<p>The forces on the atoms are dynamically scaled during the simulation,
the rescaling is done in the following manner:</p>
<img alt="_images/fix_ti_rs_force.jpg" class="align-center" src="_images/fix_ti_rs_force.jpg" />
<p>where F_int is the total force on the atoms due to the interatomic
potential and lambda is the coupling parameter of the thermodynamic
integration.</p>
<p>The fix acts as follows: during the first <em>t_equil</em> steps after the
fix is defined the value of lambda is <em>lambda_initial</em> , this is the
period to equilibrate the system in the lambda = <em>lambda_initial</em>
state. After this the value of lambda changes continuously from
<em>lambda_initial</em> to <em>lambda_final</em> according to the function defined
using the keyword <em>function</em> (described below), this is done in
<em>t_switch</em> steps. Then comes the second equilibration period of
<em>t_equil</em> to equilibrate the system in the lambda = <em>lambda_final</em>
state. After that the switching back to the lambda = <em>lambda_initial</em>
state is done using <em>t_switch</em> timesteps and following the same
switching function. After this period the value of lambda is kept
equal to <em>lambda_initial</em> indefinitely or until a <a class="reference internal" href="unfix.html"><span class="doc">unfix</span></a>
erase the fix.</p>
<p>The description of thermodynamic integration in both directions is
done in <a class="reference internal" href="#dekoning00b"><span class="std std-ref">de Koning00b</span></a>, the main reason is to try to
eliminate the dissipated heat due to the nonequilibrium process.</p>
<p>The <em>function</em> keyword allows the use of three different switching
rates. The option <em>1</em> results in a constant rescaling where the lambda
parameter changes at a constant rate during the switching time
according to the switching function</p>
<img alt="_images/fix_ti_rs_function_1.jpg" class="align-center" src="_images/fix_ti_rs_function_1.jpg" />
<p>where tau is the scaled time variable t/t_switch. This switching
function has the characteristic that the temperature scaling is faster
at temperatures closer to the final temperature of the procedure. The
option number <em>2</em> performs the switching at a rate defined by the
following switching function</p>
<img alt="_images/fix_ti_rs_function_2.jpg" class="align-center" src="_images/fix_ti_rs_function_2.jpg" />
<p>This switching function has the characteristic that the temperature
scaling occurs at a constant rate during all the procedure. The option
number <em>3</em> performs the switching at a rate defined by the following
switching function</p>
<img alt="_images/fix_ti_rs_function_3.jpg" class="align-center" src="_images/fix_ti_rs_function_3.jpg" />
<p>This switching function has the characteristic that the temperature
scaling is faster at temperatures closer to the initial temperature of
the procedure.</p>
<p>An example script using this command is provided in the
examples/USER/misc/ti directory.</p>
</div>
<div class="section" id="restart-fix-modify-output-run-start-stop-minimize-info">
<h2>Restart, fix_modify, output, run start/stop, minimize info</h2>
<p>No information about this fix is written to <a class="reference internal" href="restart.html"><span class="doc">binary restart files</span></a>.</p>
<p>This fix computes a global vector quantitie which can be accessed by
various <a class="reference internal" href="Section_howto.html#howto-15"><span class="std std-ref">output commands</span></a>. The vector has
2 positions, the first one is the coupling parameter lambda and the
second one is the time derivative of lambda. The scalar and vector
values calculated by this fix are &#8220;extensive&#8221;.</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"><span class="doc">run</span></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"><span class="doc">minimize</span></a> command.</p>
</div>
<div class="section" id="related-commands">
<h2>Related commands</h2>
<p><a class="reference internal" href="fix_ti_spring.html"><span class="doc">fix ti/spring</span></a></p>
</div>
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<p>This command is part of the USER-MISC package. It is only enabled if
LAMMPS was built with those packages. See the <a class="reference internal" href="Section_start.html#start-3"><span class="std std-ref">Making LAMMPS</span></a> section for more info.</p>
</div>
<div class="section" id="default">
<h2>Default</h2>
<p>The keyword default is function = 1.</p>
<hr class="docutils" />
<p id="dekoning99"><strong>(de Koning 99)</strong> M. de Koning, A. Antonelli and S. Yip, Phys Rev Lett, 83, 3973 (1999).</p>
<p id="watanabe"><strong>(Watanabe)</strong> M. Watanabe and W. P. Reinhardt, Phys Rev Lett, 65, 3301 (1990).</p>
<p id="dekoning96"><strong>(de Koning 96)</strong> M. de Koning and A. Antonelli, Phys Rev E, 53, 465 (1996).</p>
<p id="dekoning00a"><strong>(de Koning 00a)</strong> M. de Koning, A. Antonelli and S. Yip, J Chem Phys, 115, 11025 (2000).</p>
<p id="dekoning00b"><strong>(de Koning 00b)</strong> M. de Koning et al., Computing in Science &amp; Engineering, 2, 88 (2000).</p>
</div>
</div>
</div>
</div>
<footer>
<hr/>
<div role="contentinfo">
<p>
&copy; Copyright 2013 Sandia Corporation.
</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:'./',
VERSION:'',
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>
c4science · Help