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<li>fix langevin/eff command</li>
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<div class="section" id="fix-langevin-eff-command">
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<span id="index-0"></span><h1>fix langevin/eff command<a class="headerlink" href="#fix-langevin-eff-command" title="Permalink to this headline">¶</a></h1>
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<div class="section" id="syntax">
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<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>fix ID group-ID langevin/eff Tstart Tstop damp seed keyword values ...
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</pre></div>
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</div>
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<ul class="simple">
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<li>ID, group-ID are documented in <a class="reference internal" href="fix.html"><em>fix</em></a> command</li>
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<li>langevin/eff = style name of this fix command</li>
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<li>Tstart,Tstop = desired temperature at start/end of run (temperature units)</li>
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<li>damp = damping parameter (time units)</li>
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<li>seed = random number seed to use for white noise (positive integer)</li>
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<li>zero or more keyword/value pairs may be appended</li>
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</ul>
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<pre class="literal-block">
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keyword = <em>scale</em> or <em>tally</em> or <em>zero</em>
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<em>scale</em> values = type ratio
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type = atom type (1-N)
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ratio = factor by which to scale the damping coefficient
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<em>tally</em> values = <em>no</em> or <em>yes</em>
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<em>no</em> = do not tally the energy added/subtracted to atoms
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<em>yes</em> = do tally the energy added/subtracted to atoms
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</pre>
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<pre class="literal-block">
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<em>zero</em> value = <em>no</em> or <em>yes</em>
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<em>no</em> = do not set total random force to zero
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<em>yes</em> = set total random force to zero
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</pre>
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</div>
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<div class="section" id="examples">
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<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>fix 3 boundary langevin/eff 1.0 1.0 10.0 699483
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fix 1 all langevin/eff 1.0 1.1 10.0 48279 scale 3 1.5
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</pre></div>
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</div>
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</div>
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<div class="section" id="description">
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<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
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<p>Apply a Langevin thermostat as described in <a class="reference internal" href="#schneider"><span>(Schneider)</span></a>
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to a group of nuclei and electrons in the <a class="reference internal" href="pair_eff.html"><em>electron force field</em></a> model. Used with <a class="reference internal" href="fix_nve_eff.html"><em>fix nve/eff</em></a>,
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this command performs Brownian dynamics (BD), since the total force on
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each atom will have the form:</p>
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<div class="highlight-python"><div class="highlight"><pre>F = Fc + Ff + Fr
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Ff = - (m / damp) v
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Fr is proportional to sqrt(Kb T m / (dt damp))
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</pre></div>
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</div>
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<p>Fc is the conservative force computed via the usual inter-particle
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interactions (<a class="reference internal" href="pair_style.html"><em>pair_style</em></a>).</p>
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<p>The Ff and Fr terms are added by this fix on a per-particle basis.</p>
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<p>The operation of this fix is exactly like that described by the <a class="reference internal" href="fix_langevin.html"><em>fix langevin</em></a> command, except that the thermostatting
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is also applied to the radial electron velocity for electron
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particles.</p>
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</div>
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<div class="section" id="restart-fix-modify-output-run-start-stop-minimize-info">
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<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>
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<p>No information about this fix is written to <a class="reference internal" href="restart.html"><em>binary restart files</em></a>. Because the state of the random number generator
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is not saved in restart files, this means you cannot do “exact”
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restarts with this fix, where the simulation continues on the same as
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if no restart had taken place. However, in a statistical sense, a
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restarted simulation should produce the same behavior.</p>
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<p>The <a class="reference internal" href="fix_modify.html"><em>fix_modify</em></a> <em>temp</em> option is supported by this
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fix. You can use it to assign a temperature <a class="reference internal" href="compute.html"><em>compute</em></a>
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you have defined to this fix which will be used in its thermostatting
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procedure, as described above. For consistency, the group used by
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this fix and by the compute should be the same.</p>
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<p>The <a class="reference internal" href="fix_modify.html"><em>fix_modify</em></a> <em>energy</em> option is supported by this
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fix to add the energy change induced by Langevin thermostatting to the
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system’s potential energy as part of <a class="reference internal" href="thermo_style.html"><em>thermodynamic output</em></a>. Note that use of this option requires
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setting the <em>tally</em> keyword to <em>yes</em>.</p>
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<p>This fix computes a global scalar which can be accessed by various
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<a class="reference internal" href="Section_howto.html#howto-15"><span>output commands</span></a>. The scalar is the
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cummulative energy change due to this fix. The scalar value
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calculated by this fix is “extensive”. Note that calculation of this
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quantity requires setting the <em>tally</em> keyword to <em>yes</em>.</p>
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<p>This fix can ramp its target temperature over multiple runs, using the
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<em>start</em> and <em>stop</em> keywords of the <a class="reference internal" href="run.html"><em>run</em></a> command. See the
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<a class="reference internal" href="run.html"><em>run</em></a> command for details of how to do this.</p>
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<p>This fix is not invoked during <a class="reference internal" href="minimize.html"><em>energy minimization</em></a>.</p>
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</div>
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<div class="section" id="restrictions">
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<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
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<blockquote>
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<div>none</div></blockquote>
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<p>This fix is part of the USER-EFF package. It is only enabled if
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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>
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</div>
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<div class="section" id="related-commands">
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<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
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<p><a class="reference internal" href="fix_langevin.html"><em>fix langevin</em></a></p>
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</div>
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<div class="section" id="default">
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<h2>Default<a class="headerlink" href="#default" title="Permalink to this headline">¶</a></h2>
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<p>The option defaults are scale = 1.0 for all types and tally = no.</p>
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<hr class="docutils" />
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<p id="dunweg"><strong>(Dunweg)</strong> Dunweg and Paul, Int J of Modern Physics C, 2, 817-27 (1991).</p>
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<p id="schneider"><strong>(Schneider)</strong> Schneider and Stoll, Phys Rev B, 17, 1302 (1978).</p>
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