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<title>compute temp/rotate command — LAMMPS 15 May 2015 version documentation</title>
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<li class="toctree-l1"><a class="reference internal" href="Section_accelerate.html">5. Accelerating LAMMPS performance</a></li>
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<li>compute temp/rotate command</li>
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<div class="section" id="compute-temp-rotate-command">
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<span id="index-0"></span><h1>compute temp/rotate command<a class="headerlink" href="#compute-temp-rotate-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>compute ID group-ID temp/rotate
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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="compute.html"><em>compute</em></a> command</li>
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<li>temp/rotate = style name of this compute command</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>compute Tbead bead temp/rotate
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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>Define a computation that calculates the temperature of a group of
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atoms, after subtracting out the center-of-mass velocity and angular velocity of the group.
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This is useful if the group is expected to have a non-zero net
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velocity and/or global rotation motion for some reason. A compute of this style can be used by any
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command that computes a temperature,
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e.g. <a class="reference internal" href="thermo_modify.html"><em>thermo_modify</em></a>, <a class="reference internal" href="fix_temp_rescale.html"><em>fix temp/rescale</em></a>, <a class="reference internal" href="fix_nh.html"><em>fix npt</em></a>, etc.</p>
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<p>After the center-of-mass velocity and angular velocity has been subtracted from each atom,
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the temperature is calculated by the formula KE = dim/2 N k T, where
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KE = total kinetic energy of the group of atoms (sum of 1/2 m v^2),
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dim = 2 or 3 = dimensionality of the simulation, N = number of atoms
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in the group, k = Boltzmann constant, and T = temperature.</p>
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<p>A kinetic energy tensor, stored as a 6-element vector, is also
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calculated by this compute for use in the computation of a pressure
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tensor. The formula for the components of the tensor is the same as
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the above formula, except that v^2 is replaced by vx*vy for the xy
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component, etc. The 6 components of the vector are ordered xx, yy,
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zz, xy, xz, yz.</p>
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<p>The number of atoms contributing to the temperature is assumed to be
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constant for the duration of the run; use the <em>dynamic</em> option of the
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<a class="reference internal" href="compute_modify.html"><em>compute_modify</em></a> command if this is not the case.</p>
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<p>The removal of the center-of-mass velocity and angular velocity by this fix is essentially
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computing the temperature after a “bias” has been removed from the
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velocity of the atoms. If this compute is used with a fix command
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that performs thermostatting then this bias will be subtracted from
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each atom, thermostatting of the remaining thermal velocity will be
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performed, and the bias will be added back in. Thermostatting fixes
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that work in this way include <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_temp_berendsen.html"><em>fix temp/berendsen</em></a>, and <a class="reference internal" href="fix_langevin.html"><em>fix langevin</em></a>.</p>
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<p>This compute subtracts out degrees-of-freedom due to fixes that
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constrain molecular motion, such as <a class="reference internal" href="fix_shake.html"><em>fix shake</em></a> and
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<a class="reference internal" href="fix_rigid.html"><em>fix rigid</em></a>. This means the temperature of groups of
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atoms that include these constraints will be computed correctly. If
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needed, the subtracted degrees-of-freedom can be altered using the
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<em>extra</em> option of the <a class="reference internal" href="compute_modify.html"><em>compute_modify</em></a> command.</p>
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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><strong>Output info:</strong></p>
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<p>This compute calculates a global scalar (the temperature) and a global
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vector of length 6 (KE tensor), which can be accessed by indices 1-6.
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These values can be used by any command that uses global scalar or
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vector values from a compute as input. See <a class="reference internal" href="Section_howto.html#howto-15"><span>this section</span></a> for an overview of LAMMPS output
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options.</p>
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<p>The scalar value calculated by this compute is “intensive”. The
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vector values are “extensive”.</p>
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<p>The scalar value will be in temperature <a class="reference internal" href="units.html"><em>units</em></a>. The
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vector values will be in energy <a class="reference internal" href="units.html"><em>units</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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<p>This compute is part of the USER-MISC 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="compute_temp.html"><em>compute temp</em></a></p>
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<p><strong>Default:</strong> none</p>
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