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<div class="section" id="fix-nph-body-command">
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<span id="index-0"></span><h1>fix nph/body command<a class="headerlink" href="#fix-nph-body-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 nph/body args keyword value ...
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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>nph/body = 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"><em>fix nph</em></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<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 1 all nph/body iso 0.0 0.0 1000.0
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fix 2 all nph/body x 5.0 5.0 1000.0
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fix 2 all nph/body x 5.0 5.0 1000.0 drag 0.2
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fix 2 water nph/body aniso 0.0 0.0 1000.0 dilate partial
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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>Perform constant NPH integration to update position, velocity,
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orientation, and angular velocity each timestep for body
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particles in the group using a Nose/Hoover pressure
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barostat. P is pressure; H is enthalpy. This creates a system
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trajectory consistent with the isenthalpic ensemble.</p>
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<p>This fix differs from the <a class="reference internal" href="fix_nh.html"><em>fix nph</em></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"><em>fix nph</em></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/body” and
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“pressure”, as if these commands had been issued:</p>
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<div class="highlight-python"><div class="highlight"><pre>compute fix-ID_temp all temp/body
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compute fix-ID_press all pressure fix-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_body.html"><em>compute temp/body</em></a> and <a class="reference internal" href="compute_pressure.html"><em>compute pressure</em></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"><em>thermo_style</em></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"><em>compute_modify</em></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"><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> 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>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"><em>Section_accelerate</em></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>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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<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>This fix writes the state of the Nose/Hoover barostat to <a class="reference internal" href="restart.html"><em>binary restart files</em></a>. See the <a class="reference internal" href="read_restart.html"><em>read_restart</em></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"><em>fix_modify</em></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"><em>compute</em></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"><em>fix_modify</em></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"><em>thermodynamic output</em></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"><em>fix nph</em></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"><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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<p>This fix is part of the BODY package. It is only enabled if LAMMPS
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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>This fix requires that atoms store torque and angular momementum and a
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quaternion as defined by the <a class="reference internal" href="atom_style.html"><em>atom_style body</em></a>
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command.</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="fix_nh.html"><em>fix nph</em></a>, <a class="reference internal" href="fix_nve_body.html"><em>fix nve_body</em></a>, <a class="reference internal" href="fix_nvt_body.html"><em>fix nvt_body</em></a>, <a class="reference internal" href="fix_npt_body.html"><em>fix npt_body</em></a>, <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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