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<div class="section" id="fix-temp-csvr-command">
<span id="index-0"></span><h1>fix temp/csvr command<a class="headerlink" href="#fix-temp-csvr-command" title="Permalink to this headline"></a></h1>
</div>
<div class="section" id="fix-temp-csld-command">
<h1>fix temp/csld command<a class="headerlink" href="#fix-temp-csld-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 temp/csvr Tstart Tstop Tdamp seed
</pre></div>
</div>
<div class="highlight-python"><div class="highlight"><pre>fix ID group-ID temp/csld Tstart Tstop Tdamp seed
</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>temp/csvr or temp/csld = style name of this fix command</li>
<li>Tstart,Tstop = desired temperature at start/end of run</li>
</ul>
<div class="highlight-python"><div class="highlight"><pre>Tstart can be a variable (see below)
</pre></div>
</div>
<ul class="simple">
<li>Tdamp = temperature damping parameter (time units)</li>
<li>seed = random number seed to use for white noise (positive integer)</li>
</ul>
</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 1 all temp/csvr 300.0 300.0 100.0 54324
</pre></div>
</div>
<div class="highlight-python"><div class="highlight"><pre>fix 1 all temp/csld 100.0 300.0 10.0 123321
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline"></a></h2>
<p>Adjust the temperature with a canonical sampling thermostat that uses
global velocity rescaling with Hamiltonian dynamics (<em>temp/csvr</em>)
<a class="reference internal" href="#bussi1"><span>(Bussi1)</span></a>, or Langevin dynamics (<em>temp/csld</em>)
<a class="reference internal" href="#bussi2"><span>(Bussi2)</span></a>. In the case of <em>temp/csvr</em> the thermostat is
similar to the empirical Berendsen thermostat in
<a class="reference internal" href="fix_temp_berendsen.html"><em>temp/berendsen</em></a>, but chooses the actual
scaling factor from a suitably chosen (gaussian) distribution rather
than having it determined from the time constant directly. In the case
of <em>temp/csld</em> the velocities are updated to a linear combination of
the current velocities with a gaussian distribution of velocities at
the desired temperature. Both termostats are applied every timestep.</p>
<p>The thermostat is applied to only the translational degrees of freedom
for the particles, which is an important consideration for finite-size
particles which have rotational degrees of freedom are being
thermostatted with these fixes. The translational degrees of freedom
can also have a bias velocity removed from them before thermostatting
takes place; see the description below.</p>
<p>The desired temperature at each timestep is a ramped value during the
run from <em>Tstart</em> to <em>Tstop</em>. The <em>Tdamp</em> parameter is specified in
time units and determines how rapidly the temperature is relaxed. For
example, a value of 100.0 means to relax the temperature in a timespan
of (roughly) 100 time units (tau or fmsec or psec - see the
<a class="reference internal" href="units.html"><em>units</em></a> command).</p>
<p><em>Tstart</em> can be specified as an equal-style <a class="reference internal" href="variable.html"><em>variable</em></a>.
In this case, the <em>Tstop</em> setting is ignored. If the value is a
variable, it should be specified as v_name, where name is the variable
name. In this case, the variable will be evaluated each timestep, and
its value used to determine the target temperature.</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
keywords for the simulation box parameters and timestep and elapsed
time. Thus it is easy to specify a time-dependent temperature.</p>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p class="last">Unlike the <a class="reference internal" href="fix_nh.html"><em>fix nvt</em></a> command which
performs Nose/Hoover thermostatting AND time integration, these fixes
do NOT perform time integration. They only modify velocities to effect
thermostatting. Thus you must use a separate time integration fix,
like <a class="reference internal" href="fix_nve.html"><em>fix nve</em></a> to actually update the positions of atoms
using the modified velocities. Likewise, these fixes should not
normally be used on atoms that also have their temperature controlled
by another fix - e.g. by <a class="reference internal" href="fix_nh.html"><em>fix nvt</em></a> or <a class="reference internal" href="fix_langevin.html"><em>fix langevin</em></a> commands.</p>
</div>
<p>See <a class="reference internal" href="Section_howto.html#howto-16"><span>this howto section</span></a> of the manual for
a discussion of different ways to compute temperature and perform
thermostatting.</p>
<p>These fixes compute a temperature each timestep. To do this, the fix
creates its own compute of style &#8220;temp&#8221;, as if this command had been
issued:</p>
<div class="highlight-python"><div class="highlight"><pre>compute fix-ID_temp group-ID temp
</pre></div>
</div>
<p>See the <a class="reference internal" href="compute_temp.html"><em>compute temp</em></a> command for details. Note
that the ID of the new compute is the fix-ID + underscore + &#8220;temp&#8221;,
and the group for the new compute is the same as the fix group.</p>
<p>Note that this is NOT the compute used by thermodynamic output (see
the <a class="reference internal" href="thermo_style.html"><em>thermo_style</em></a> command) with ID = <em>thermo_temp</em>.
This means you can change the attributes of this fix&#8217;s temperature
(e.g. its degrees-of-freedom) via the
<a class="reference internal" href="compute_modify.html"><em>compute_modify</em></a> command or print this temperature
during thermodynamic output via the <a class="reference internal" href="thermo_style.html"><em>thermo_style custom</em></a> command using the appropriate compute-ID.
It also means that changing attributes of <em>thermo_temp</em> will have no
effect on this fix.</p>
<p>Like other fixes that perform thermostatting, these fixes can be used
with <a class="reference internal" href="compute.html"><em>compute commands</em></a> that calculate a temperature
after removing a &#8220;bias&#8221; from the atom velocities. E.g. removing the
center-of-mass velocity from a group of atoms or only calculating
temperature on the x-component of velocity or only calculating
temperature for atoms in a geometric region. This is not done by
default, but only if the <a class="reference internal" href="fix_modify.html"><em>fix_modify</em></a> command is used
to assign a temperature compute to this fix that includes such a bias
term. See the doc pages for individual <a class="reference internal" href="compute.html"><em>compute commands</em></a> to determine which ones include a bias. In
this case, the thermostat works in the following manner: the current
temperature is calculated taking the bias into account, bias is
removed from each atom, thermostatting is performed on the remaining
thermal degrees of freedom, and the bias is added back in.</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 these fixes are 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>temp</em> option is supported by these
fixes. You can use it to assign a temperature <a class="reference internal" href="compute.html"><em>compute</em></a>
you have defined to these fixes which will be used in its thermostatting
procedure, as described above. For consistency, the group used by
these fixes and by the compute should be the same.</p>
<p>These fixes can ramp its target temperature over multiple runs, using
the <em>start</em> and <em>stop</em> keywords of the <a class="reference internal" href="run.html"><em>run</em></a> command. See the
<a class="reference internal" href="run.html"><em>run</em></a> command for details of how to do this.</p>
<p>These fixes are not invoked during <a class="reference internal" href="minimize.html"><em>energy minimization</em></a>.</p>
<p>These fixes compute a global scalar 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
cummulative energy change due to the fix. The scalar value
calculated by this fix is &#8220;extensive&#8221;.</p>
</div>
<div class="section" id="restrictions">
<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline"></a></h2>
<p>These fixes are not compatible with <a class="reference internal" href="fix_shake.html"><em>fix shake</em></a>.</p>
<p>The fix can be used with dynamic groups as defined by the
<a class="reference internal" href="group.html"><em>group</em></a> command. Likewise it can be used with groups to
which atoms are added or deleted over time, e.g. a deposition
simulation. However, the conservation properties of the thermostat
and barostat are defined for systems with a static set of atoms. You
may observe odd behavior if the atoms in a group vary dramatically
over time or the atom count becomes very small.</p>
</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_nve.html"><em>fix nve</em></a>, <a class="reference internal" href="fix_nh.html"><em>fix nvt</em></a>, <a class="reference internal" href="fix_temp_rescale.html"><em>fix temp/rescale</em></a>, <a class="reference internal" href="fix_langevin.html"><em>fix langevin</em></a>,
<a class="reference internal" href="fix_modify.html"><em>fix_modify</em></a>, <a class="reference internal" href="compute_temp.html"><em>compute temp</em></a>,
<a class="reference internal" href="fix_temp_berendsen.html"><em>fix temp/berendsen</em></a></p>
<p><strong>Default:</strong> none</p>
<hr class="docutils" />
<p id="bussi2"><span id="bussi1"></span><strong>(Bussi1)</strong> Bussi, Donadio and Parrinello, J. Chem. Phys. 126, 014101(2007)</p>
<p><strong>(Bussi2)</strong> Bussi and Parrinello, Phys. Rev. E 75, 056707 (2007)</p>
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