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<li class="toctree-l1"><a class="reference internal" href="Section_intro.html">1. Introduction</a></li>
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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 class="toctree-l1"><a class="reference internal" href="Section_errors.html">12. Errors</a></li>
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<li>compute temp/ramp command</li>
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<div class="section" id="compute-temp-ramp-command">
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<span id="index-0"></span><h1>compute temp/ramp command</h1>
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<div class="section" id="syntax">
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<h2>Syntax</h2>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">compute</span> <span class="n">ID</span> <span class="n">group</span><span class="o">-</span><span class="n">ID</span> <span class="n">temp</span><span class="o">/</span><span class="n">ramp</span> <span class="n">vdim</span> <span class="n">vlo</span> <span class="n">vhi</span> <span class="n">dim</span> <span class="n">clo</span> <span class="n">chi</span> <span class="n">keyword</span> <span class="n">value</span> <span class="o">...</span>
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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"><span class="doc">compute</span></a> command</li>
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<li>temp/ramp = style name of this compute command</li>
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<li>vdim = <em>vx</em> or <em>vy</em> or <em>vz</em></li>
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<li>vlo,vhi = subtract velocities between vlo and vhi (velocity units)</li>
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<li>dim = <em>x</em> or <em>y</em> or <em>z</em></li>
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<li>clo,chi = lower and upper bound of domain to subtract from (distance units)</li>
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<li>zero or more keyword/value pairs may be appended</li>
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<li>keyword = <em>units</em></li>
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</ul>
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<pre class="literal-block">
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<em>units</em> value = <em>lattice</em> or <em>box</em>
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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</h2>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">compute</span> <span class="mi">2</span><span class="n">nd</span> <span class="n">middle</span> <span class="n">temp</span><span class="o">/</span><span class="n">ramp</span> <span class="n">vx</span> <span class="mi">0</span> <span class="mi">8</span> <span class="n">y</span> <span class="mi">2</span> <span class="mi">12</span> <span class="n">units</span> <span class="n">lattice</span>
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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</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 an ramped velocity profile before
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computing the kinetic energy. A compute of this style can be used by
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any command that computes a temperature,
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e.g. <a class="reference internal" href="thermo_modify.html"><span class="doc">thermo_modify</span></a>, <a class="reference internal" href="fix_temp_rescale.html"><span class="doc">fix temp/rescale</span></a>, <a class="reference internal" href="fix_nh.html"><span class="doc">fix npt</span></a>, etc.</p>
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<p>The meaning of the arguments for this command which define the
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velocity ramp are the same as for the <a class="reference internal" href="velocity.html"><span class="doc">velocity ramp</span></a>
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command which was presumably used to impose the velocity.</p>
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<p>After the ramp velocity has been subtracted from the specified
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dimension for each atom, the temperature is calculated by the formula
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KE = dim/2 N k T, where KE = total kinetic energy of the group of
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atoms (sum of 1/2 m v^2), dim = 2 or 3 = dimensionality of the
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simulation, N = number of atoms in the group, k = Boltzmann constant,
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and T = temperature.</p>
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<p>The <em>units</em> keyword determines the meaning of the distance units used
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for coordinates (c1,c2) and velocities (vlo,vhi). A <em>box</em> value
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selects standard distance units as defined by the <a class="reference internal" href="units.html"><span class="doc">units</span></a>
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command, e.g. Angstroms for units = real or metal. A <em>lattice</em> value
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means the distance units are in lattice spacings; e.g. velocity =
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lattice spacings / tau. The <a class="reference internal" href="lattice.html"><span class="doc">lattice</span></a> command must have
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been previously used to define the lattice spacing.</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"><span class="doc">compute_modify</span></a> command if this is not the case.</p>
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<p>The removal of the ramped velocity component by this fix is
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essentially computing the temperature after a “bias” has been removed
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from the velocity of the atoms. If this compute is used with a fix
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command that performs thermostatting then this bias will be subtracted
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from each atom, thermostatting of the remaining thermal velocity will
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be performed, and the bias will be added back in. Thermostatting
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fixes that work in this way include <a class="reference internal" href="fix_nh.html"><span class="doc">fix nvt</span></a>, <a class="reference internal" href="fix_temp_rescale.html"><span class="doc">fix temp/rescale</span></a>, <a class="reference internal" href="fix_temp_berendsen.html"><span class="doc">fix temp/berendsen</span></a>, and <a class="reference internal" href="fix_langevin.html"><span class="doc">fix langevin</span></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"><span class="doc">fix shake</span></a> and
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<a class="reference internal" href="fix_rigid.html"><span class="doc">fix rigid</span></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"><span class="doc">compute_modify</span></a> command.</p>
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<p>See <a class="reference internal" href="Section_howto.html#howto-16"><span class="std std-ref">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 class="std std-ref">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"><span class="doc">units</span></a>. The
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vector values will be in energy <a class="reference internal" href="units.html"><span class="doc">units</span></a>.</p>
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</div>
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<div class="section" id="restrictions">
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<h2>Restrictions</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</h2>
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<p><a class="reference internal" href="compute_temp.html"><span class="doc">compute temp</span></a>, <a class="reference internal" href="compute_temp_profile.html"><span class="doc">compute temp/profie</span></a>, <a class="reference internal" href="compute_temp_deform.html"><span class="doc">compute temp/deform</span></a>, <a class="reference internal" href="compute_pressure.html"><span class="doc">compute pressure</span></a></p>
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</div>
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<div class="section" id="default">
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<h2>Default</h2>
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<p>The option default is units = lattice.</p>
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