<h2>Description<aclass="headerlink"href="#description"title="Permalink to this headline">¶</a></h2>
<p>Applies Generalized Langevin Dynamics to a group of atoms, as
described in <aclass="reference internal"href="#baczewski"><span>(Baczewski)</span></a>. This is intended to model the
effect of an implicit solvent with a temporally non-local dissipative
force and a colored Gaussian random force, consistent with the
Fluctuation-Dissipation Theorem. The functional form of the memory
kernel associated with the temporally non-local force is constrained
to be a Prony series.</p>
<divclass="admonition warning">
<pclass="first admonition-title">Warning</p>
<pclass="last">While this fix bears many similarities to <aclass="reference internal"href="fix_langevin.html"><em>fix langevin</em></a>, it has one significant
difference. Namely, <aclass="reference internal"href=""><em>fix gld</em></a> performs time integration,
whereas <aclass="reference internal"href="fix_langevin.html"><em>fix langevin</em></a> does NOT. To this end, the
specification of another fix to perform time integration, such as <aclass="reference internal"href="fix_nve.html"><em>fix nve</em></a>, is NOT necessary.</p>
</div>
<p>With this fix active, the force on the <ahref="#id1"><spanclass="problematic"id="id2">*</span></a>j*th atom is given as</p>
<p>The desired temperature at each timestep is ramped from <em>Tstart</em> to
<em>Tstop</em> over the course of the next run.</p>
<p>The random # <em>seed</em> must be a positive integer. A Marsaglia random
number generator is used. Each processor uses the input seed to
generate its own unique seed and its own stream of random
numbers. Thus the dynamics of the system will not be identical on two
runs on different numbers of processors.</p>
<hrclass="docutils"/>
<p>The keyword/value option pairs are used in the following ways.</p>
<p>The keyword <em>frozen</em> can be used to specify how the extended variables
associated with the GLD memory kernel are initialized. Specifying no
(the default), the initial values are drawn at random from an
equilibrium distribution at <em>Tstart</em>, consistent with the
Fluctuation-Dissipation Theorem. Specifying yes, initializes the
extended variables to zero.</p>
<p>The keyword <em>zero</em> can be used to eliminate drift due to the
thermostat. Because the random forces on different atoms are
independent, they do not sum exactly to zero. As a result, this fix
applies a small random force to the entire system, and the
center-of-mass of the system undergoes a slow random walk. If the
keyword <em>zero</em> is set to <em>yes</em>, the total random force is set exactly
to zero by subtracting off an equal part of it from each atom in the
group. As a result, the center-of-mass of a system with zero initial
momentum will not drift over time.</p>
<hrclass="docutils"/>
<p><strong>Restart, run start/stop, minimize info:</strong></p>
<p>The instantaneous values of the extended variables are written to
<aclass="reference internal"href="restart.html"><em>binary restart files</em></a>. Because the state of the random
number generator is not saved in restart files, this means you cannot
do “exact” restarts with this fix, where the simulation continues on
the same as if no restart had taken place. However, in a statistical
sense, a restarted simulation should produce the same behavior.</p>
<p>None of the <aclass="reference internal"href="fix_modify.html"><em>fix_modify</em></a> options are relevant to this
fix. No global or per-atom quantities are stored by this fix for
access by various <aclass="reference internal"href="Section_howto.html#howto-15"><span>output commands</span></a>.</p>
<p>This fix can ramp its target temperature over multiple runs, using the
<em>start</em> and <em>stop</em> keywords of the <aclass="reference internal"href="run.html"><em>run</em></a> command. See the
<aclass="reference internal"href="run.html"><em>run</em></a> command for details of how to do this.</p>
<p>This fix is not invoked during <aclass="reference internal"href="minimize.html"><em>energy minimization</em></a>.</p>
</div>
<divclass="section"id="restrictions">
<h2>Restrictions<aclass="headerlink"href="#restrictions"title="Permalink to this headline">¶</a></h2>
<p>This fix is part of the MISC package. It is only enabled if LAMMPS
was built with that package. See the <aclass="reference internal"href="Section_start.html#start-3"><span>Making LAMMPS</span></a> section for more info.</p>
</div>
<divclass="section"id="related-commands">
<h2>Related commands<aclass="headerlink"href="#related-commands"title="Permalink to this headline">¶</a></h2>
Built with <ahref="http://sphinx-doc.org/">Sphinx</a> using a <ahref="https://github.com/snide/sphinx_rtd_theme">theme</a> provided by <ahref="https://readthedocs.org">Read the Docs</a>.