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<div class="section" id="fix-nph-sphere-command">
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<span id="index-0"></span><h1>fix nph/sphere command</h1>
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</div>
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<div class="section" id="fix-nph-sphere-omp-command">
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<h1>fix nph/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">nph</span><span class="o">/</span><span class="n">sphere</span> <span class="n">args</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>nph/sphere = style name of this fix command</li>
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<li>additional barostat related keyword/value pairs from the <a class="reference internal" href="fix_nh.html"><span class="doc">fix nph</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">nph</span><span class="o">/</span><span class="n">sphere</span> <span class="n">iso</span> <span class="mf">0.0</span> <span class="mf">0.0</span> <span class="mf">1000.0</span>
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<span class="n">fix</span> <span class="mi">2</span> <span class="nb">all</span> <span class="n">nph</span><span class="o">/</span><span class="n">sphere</span> <span class="n">x</span> <span class="mf">5.0</span> <span class="mf">5.0</span> <span class="mf">1000.0</span>
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<span class="n">fix</span> <span class="mi">2</span> <span class="nb">all</span> <span class="n">nph</span><span class="o">/</span><span class="n">sphere</span> <span class="n">x</span> <span class="mf">5.0</span> <span class="mf">5.0</span> <span class="mf">1000.0</span> <span class="n">drag</span> <span class="mf">0.2</span>
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<span class="n">fix</span> <span class="mi">2</span> <span class="n">water</span> <span class="n">nph</span><span class="o">/</span><span class="n">sphere</span> <span class="n">aniso</span> <span class="mf">0.0</span> <span class="mf">0.0</span> <span class="mf">1000.0</span> <span class="n">dilate</span> <span class="n">partial</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 NPH 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 pressure barostat. P is pressure; H is
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enthalpy. This creates a system trajectory consistent with the
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isenthalpic ensemble.</p>
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<p>This fix differs from the <a class="reference internal" href="fix_nh.html"><span class="doc">fix nph</span></a> command, which assumes
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point particles and only updates their position and velocity.</p>
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<p>Additional parameters affecting the barostat are specified by keywords
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and values documented with the <a class="reference internal" href="fix_nh.html"><span class="doc">fix nph</span></a> command. See,
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for example, discussion of the <em>aniso</em>, and <em>dilate</em> keywords.</p>
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<p>The particles in the fix group are the only ones whose velocities and
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positions are updated by the velocity/position update portion of the
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NPH integration.</p>
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<p>Regardless of what particles are in the fix group, a global pressure is
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computed for all particles. Similarly, when the size of the simulation
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box is changed, all particles are re-scaled to new positions, unless the
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keyword <em>dilate</em> is specified with a value of <em>partial</em>, in which case
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only the particles in the fix group are re-scaled. The latter can be
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useful for leaving the coordinates of particles in a solid substrate
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unchanged and controlling the pressure of a surrounding fluid.</p>
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<hr class="docutils" />
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<p>This fix computes a temperature and pressure each timestep. To do
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this, the fix creates its own computes of style “temp/sphere” and
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“pressure”, as if these commands 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="nb">all</span> <span class="n">temp</span><span class="o">/</span><span class="n">sphere</span>
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<span class="n">compute</span> <span class="n">fix</span><span class="o">-</span><span class="n">ID_press</span> <span class="nb">all</span> <span class="n">pressure</span> <span class="n">fix</span><span class="o">-</span><span class="n">ID_temp</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> and <a class="reference internal" href="compute_pressure.html"><span class="doc">compute pressure</span></a> commands for details. Note that the
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IDs of the new computes are the fix-ID + underscore + “temp” or fix_ID
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+ underscore + “press”, and the group for the new computes is “all”
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since pressure is computed for the entire system.</p>
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<p>Note that these are NOT the computes 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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and <em>thermo_press</em>. This means you can change the attributes of this
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fix’s temperature or pressure 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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or pressure 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> or
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<em>thermo_press</em> will have no effect on this fix.</p>
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<hr class="docutils" />
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<p>Styles with a <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 GPU, USER-INTEL, KOKKOS,
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USER-OMP and OPT packages, respectively. They are only enabled if
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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 barostat 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> and <em>press</em> options are
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supported by this fix. You can use them to assign a
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<a class="reference internal" href="compute.html"><span class="doc">compute</span></a> you have defined to this fix which will be used
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in its thermostatting or barostatting procedure. If you do this, note
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that the kinetic energy derived from the compute temperature should be
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consistent with the virial term computed using all atoms for the
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pressure. LAMMPS will warn you if you choose to compute temperature
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on a subset of atoms.</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 barostatting 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 nph</span></a> command.</p>
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<p>This fix can ramp its target pressure 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 nph</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_sphere.html"><span class="doc">fix nvt_sphere</span></a>, <a class="reference internal" href="fix_npt_sphere.html"><span class="doc">fix npt_sphere</span></a>,
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<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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