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