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<li>fix nvt/sphere command</li>
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<div class="section" id="fix-nvt-sphere-command">
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<span id="index-0"></span><h1>fix nvt/sphere command</h1>
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</div>
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<div class="section" id="fix-nvt-sphere-omp-command">
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<h1>fix nvt/sphere/omp 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">fix</span> <span class="n">ID</span> <span class="n">group</span><span class="o">-</span><span class="n">ID</span> <span class="n">nvt</span><span class="o">/</span><span class="n">sphere</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="fix.html"><span class="doc">fix</span></a> command</li>
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<li>nvt/sphere = style name of this fix command</li>
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<li>additional thermostat related keyword/value pairs from the <a class="reference internal" href="fix_nh.html"><span class="doc">fix nvt</span></a> command can be appended</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</h2>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">fix</span> <span class="mi">1</span> <span class="nb">all</span> <span class="n">nvt</span><span class="o">/</span><span class="n">sphere</span> <span class="n">temp</span> <span class="mf">300.0</span> <span class="mf">300.0</span> <span class="mf">100.0</span>
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<span class="n">fix</span> <span class="mi">1</span> <span class="nb">all</span> <span class="n">nvt</span><span class="o">/</span><span class="n">sphere</span> <span class="n">temp</span> <span class="mf">300.0</span> <span class="mf">300.0</span> <span class="mf">100.0</span> <span class="n">drag</span> <span class="mf">0.2</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>Perform constant NVT integration to update position, velocity, and
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angular velocity each timestep for finite-size spherical particles in
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the group using a Nose/Hoover temperature thermostat. V is volume; T
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is temperature. This creates a system trajectory consistent with the
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canonical ensemble.</p>
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<p>This fix differs from the <a class="reference internal" href="fix_nh.html"><span class="doc">fix nvt</span></a> command, which
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assumes point particles and only updates their position and velocity.</p>
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<p>The thermostat is applied to both the translational and rotational
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degrees of freedom for the spherical particles, assuming a compute is
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used which calculates a temperature that includes the rotational
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degrees of freedom (see below). 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>Additional parameters affecting the thermostat are specified by
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keywords and values documented with the <a class="reference internal" href="fix_nh.html"><span class="doc">fix nvt</span></a>
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command. See, for example, discussion of the <em>temp</em> and <em>drag</em>
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keywords.</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/sphere”, as if this command
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had been issued:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">compute</span> <span class="n">fix</span><span class="o">-</span><span class="n">ID_temp</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">sphere</span>
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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_sphere.html"><span class="doc">compute temp/sphere</span></a> command for
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details. Note that the ID of the new compute is the fix-ID +
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underscore + “temp”, and the group for the new compute is the same as
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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"><span class="doc">thermo_style</span></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"><span class="doc">compute_modify</span></a> command or print this temperature
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during thermodynamic output via the <a class="reference internal" href="thermo_style.html"><span class="doc">thermo_style custom</span></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"><span class="doc">compute commands</span></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"><span class="doc">fix_modify</span></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"><span class="doc">compute commands</span></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>, <em>gpu</em>, <em>intel</em>, <em>kk</em>, <em>omp</em>, or <em>opt</em> suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed in <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></a>
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.</p>
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<p>These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
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KOKKOS, USER-OMP and OPT packages, respectively. They are only
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enabled if LAMMPS was built with those packages. See the <a class="reference internal" href="Section_start.html#start-3"><span class="std std-ref">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 class="std std-ref">-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"><span class="doc">suffix</span></a> command in your input script.</p>
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<p>See <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></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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<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</h2>
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<p>This fix writes the state of the Nose/Hoover thermostat to <a class="reference internal" href="restart.html"><span class="doc">binary restart files</span></a>. See the <a class="reference internal" href="read_restart.html"><span class="doc">read_restart</span></a>
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command for info on how to re-specify a fix in an input script that
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reads a restart file, so that the operation of the fix continues in an
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uninterrupted fashion.</p>
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<p>The <a class="reference internal" href="fix_modify.html"><span class="doc">fix_modify</span></a> <em>temp</em> option is supported by this
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fix. You can use it to assign a <a class="reference internal" href="compute.html"><span class="doc">compute</span></a> you have
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defined to this fix which will be used in its thermostatting
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procedure.</p>
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<p>The <a class="reference internal" href="fix_modify.html"><span class="doc">fix_modify</span></a> <em>energy</em> option is supported by this
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fix to add the energy change induced by Nose/Hoover thermostatting to
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the system’s potential energy as part of <a class="reference internal" href="thermo_style.html"><span class="doc">thermodynamic output</span></a>.</p>
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<p>This fix computes the same global scalar and global vector of
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quantities as does the <a class="reference internal" href="fix_nh.html"><span class="doc">fix nvt</span></a> command.</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"><span class="doc">run</span></a> command. See the
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<a class="reference internal" href="run.html"><span class="doc">run</span></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"><span class="doc">energy minimization</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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<p>This fix requires that atoms store torque and angular velocity (omega)
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and a radius as defined by the <a class="reference internal" href="atom_style.html"><span class="doc">atom_style sphere</span></a>
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command.</p>
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<p>All particles in the group must be finite-size spheres. They cannot
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be point particles.</p>
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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="fix_nh.html"><span class="doc">fix nvt</span></a>, <a class="reference internal" href="fix_nve_sphere.html"><span class="doc">fix nve_sphere</span></a>, <a class="reference internal" href="fix_nvt_asphere.html"><span class="doc">fix nvt_asphere</span></a>, <a class="reference internal" href="fix_npt_sphere.html"><span class="doc">fix npt_sphere</span></a>, <a class="reference internal" href="fix_modify.html"><span class="doc">fix_modify</span></a></p>
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<p><strong>Default:</strong> none</p>
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</div>
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</div>
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© Copyright 2013 Sandia Corporation.
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