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<div class="section" id="fix-temp-rescale-command">
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<span id="index-0"></span><h1>fix temp/rescale command<a class="headerlink" href="#fix-temp-rescale-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="fix-temp-rescale-cuda-command">
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<h1>fix temp/rescale/cuda command<a class="headerlink" href="#fix-temp-rescale-cuda-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="fix-temp-rescale-limit-cuda-command">
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<h1>fix temp/rescale/limit/cuda command<a class="headerlink" href="#fix-temp-rescale-limit-cuda-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/rescale N Tstart Tstop window fraction
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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/rescale = style name of this fix command</li>
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<li>N = perform rescaling every N steps</li>
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<li>Tstart,Tstop = desired temperature at start/end of run (temperature units)</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>window = only rescale if temperature is outside this window (temperature units)</li>
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<li>fraction = rescale to target temperature by this fraction</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 3 flow temp/rescale 100 1.0 1.1 0.02 0.5
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fix 3 boundary temp/rescale 1 1.0 1.5 0.05 1.0
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fix 3 boundary temp/rescale 1 1.0 1.5 0.05 1.0
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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>Reset the temperature of a group of atoms by explicitly rescaling
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their velocities.</p>
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<p>The rescaling is applied to only the translational degrees of freedom
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for the particles, which is an important consideration if finite-size
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particles which have rotational degrees of freedom are being
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thermostatted with this fix. The translational degrees of freedom can
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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>Rescaling is performed every N timesteps. The target temperature is a
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ramped value between the <em>Tstart</em> and <em>Tstop</em> temperatures at the
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beginning and end of the run.</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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<p>Rescaling is only performed if the difference between the current and
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desired temperatures is greater than the <em>window</em> value. The amount
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of rescaling that is applied is a <em>fraction</em> (from 0.0 to 1.0) of the
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difference between the actual and desired temperature. E.g. if
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<em>fraction</em> = 1.0, the temperature is reset to exactly the desired
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value.</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, this fix does NOT
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perform time integration. It only modifies 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, this fix should not normally
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be used on atoms that also have their temperature controlled by
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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>This fix computes a temperature each timestep. To do this, the fix
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creates its own compute of style “temp”, as if one of this command had
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been 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> for details. Note that the
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ID of the new compute is the fix-ID + underscore + “temp”, and the
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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, this fix 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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<hr class="docutils" />
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<p>Styles with a <em>cuda</em> suffix are functionally the same as the
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corresponding style without the suffix. They have been optimized to
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run faster, depending on your available hardware, as discussed in
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<a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></a> of the manual. The
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accelerated styles take the same arguments and should produce the same
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results, except for round-off and precision issues.</p>
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<p>These accelerated styles are part of the USER-CUDA package. They are
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only enabled if 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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<p>You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the <a class="reference internal" href="Section_start.html#start-7"><span>-suffix command-line switch</span></a> when you invoke LAMMPS, or you can
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use the <a class="reference internal" href="suffix.html"><em>suffix</em></a> command in your input script.</p>
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<p>See <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></a> of the manual for
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more instructions on how to use the accelerated styles effectively.</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 this fix is 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 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 implied by a velocity rescaling 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>.</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”.</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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</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>, <a class="reference internal" href="fix_nh.html"><em>fix nvt</em></a>,
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<a class="reference internal" href="fix_modify.html"><em>fix_modify</em></a></p>
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<p><strong>Default:</strong> none</p>
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</div>
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