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<div class="section" id="fix-nph-body-command">
<span id="index-0"></span><h1>fix nph/body command</h1>
<div class="section" id="syntax">
<h2>Syntax</h2>
<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">body</span> <span class="n">args</span> <span class="n">keyword</span> <span class="n">value</span> <span class="o">...</span>
</pre></div>
</div>
<ul class="simple">
<li>ID, group-ID are documented in <a class="reference internal" href="fix.html"><span class="doc">fix</span></a> command</li>
<li>nph/body = style name of this fix command</li>
<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>
</ul>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<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">body</span> <span class="n">iso</span> <span class="mf">0.0</span> <span class="mf">0.0</span> <span class="mf">1000.0</span>
<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">body</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">fix</span> <span class="mi">2</span> <span class="nb">all</span> <span class="n">nph</span><span class="o">/</span><span class="n">body</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>
<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">body</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>
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>Perform constant NPH integration to update position, velocity,
orientation, and angular velocity each timestep for body
particles in the group using a Nose/Hoover pressure
barostat. P is pressure; H is enthalpy. This creates a system
trajectory consistent with the isenthalpic ensemble.</p>
<p>This fix differs from the <a class="reference internal" href="fix_nh.html"><span class="doc">fix nph</span></a> command, which assumes
point particles and only updates their position and velocity.</p>
<p>Additional parameters affecting the barostat are specified by keywords
and values documented with the <a class="reference internal" href="fix_nh.html"><span class="doc">fix nph</span></a> command. See,
for example, discussion of the <em>aniso</em>, and <em>dilate</em> keywords.</p>
<p>The particles in the fix group are the only ones whose velocities and
positions are updated by the velocity/position update portion of the
NPH integration.</p>
<p>Regardless of what particles are in the fix group, a global pressure is
computed for all particles. Similarly, when the size of the simulation
box is changed, all particles are re-scaled to new positions, unless the
keyword <em>dilate</em> is specified with a value of <em>partial</em>, in which case
only the particles in the fix group are re-scaled. The latter can be
useful for leaving the coordinates of particles in a solid substrate
unchanged and controlling the pressure of a surrounding fluid.</p>
<hr class="docutils" />
<p>This fix computes a temperature and pressure each timestep. To do
this, the fix creates its own computes of style &#8220;temp/body&#8221; and
&#8220;pressure&#8221;, as if these commands had been issued:</p>
<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">body</span>
<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>
</pre></div>
</div>
<p>See the <a class="reference internal" href="compute_temp_body.html"><span class="doc">compute temp/body</span></a> and <a class="reference internal" href="compute_pressure.html"><span class="doc">compute pressure</span></a> commands for details. Note that the
IDs of the new computes are the fix-ID + underscore + &#8220;temp&#8221; or fix_ID
+ underscore + &#8220;press&#8221;, and the group for the new computes is &#8220;all&#8221;
since pressure is computed for the entire system.</p>
<p>Note that these are NOT the computes used by thermodynamic output (see
the <a class="reference internal" href="thermo_style.html"><span class="doc">thermo_style</span></a> command) with ID = <em>thermo_temp</em>
and <em>thermo_press</em>. This means you can change the attributes of this
fix&#8217;s temperature or pressure via the
<a class="reference internal" href="compute_modify.html"><span class="doc">compute_modify</span></a> command or print this temperature
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.
It also means that changing attributes of <em>thermo_temp</em> or
<em>thermo_press</em> will have no effect on this fix.</p>
<hr class="docutils" />
<p>Styles with a <em>gpu</em>, <em>intel</em>, <em>kk</em>, <em>omp</em>, or <em>opt</em> suffix are
functionally the same as the corresponding style without the suffix.
They have been optimized to run faster, depending on your available
hardware, as discussed in <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></a>
of the manual. The accelerated styles take the same arguments and
should produce the same results, except for round-off and precision
issues.</p>
<p>These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
USER-OMP and OPT packages, respectively. They are only 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>
<p>You can specify the accelerated styles explicitly in your input script
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
use the <a class="reference internal" href="suffix.html"><span class="doc">suffix</span></a> command in your input script.</p>
<p>See <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></a> of the manual for
more instructions on how to use the accelerated styles effectively.</p>
</div>
<div class="section" id="restart-fix-modify-output-run-start-stop-minimize-info">
<h2>Restart, fix_modify, output, run start/stop, minimize info</h2>
<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>
command for info on how to re-specify a fix in an input script that
reads a restart file, so that the operation of the fix continues in an
uninterrupted fashion.</p>
<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
supported by this fix. You can use them to assign a
<a class="reference internal" href="compute.html"><span class="doc">compute</span></a> you have defined to this fix which will be used
in its thermostatting or barostatting procedure. If you do this, note
that the kinetic energy derived from the compute temperature should be
consistent with the virial term computed using all atoms for the
pressure. LAMMPS will warn you if you choose to compute temperature
on a subset of atoms.</p>
<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
fix to add the energy change induced by Nose/Hoover barostatting to
the system&#8217;s potential energy as part of <a class="reference internal" href="thermo_style.html"><span class="doc">thermodynamic output</span></a>.</p>
<p>This fix computes the same global scalar and global vector of
quantities as does the <a class="reference internal" href="fix_nh.html"><span class="doc">fix nph</span></a> command.</p>
<p>This fix can ramp its target pressure over multiple runs, using the
<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
<a class="reference internal" href="run.html"><span class="doc">run</span></a> command for details of how to do this.</p>
<p>This fix is not invoked during <a class="reference internal" href="minimize.html"><span class="doc">energy minimization</span></a>.</p>
</div>
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<p>This fix is part of the BODY package. It is only enabled if LAMMPS
was built with that package. 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>
<p>This fix requires that atoms store torque and angular momementum and a
quaternion as defined by the <a class="reference internal" href="atom_style.html"><span class="doc">atom_style body</span></a>
command.</p>
</div>
<div class="section" id="related-commands">
<h2>Related commands</h2>
<p><a class="reference internal" href="fix_nh.html"><span class="doc">fix nph</span></a>, <a class="reference internal" href="fix_nve_body.html"><span class="doc">fix nve_body</span></a>, <a class="reference internal" href="fix_nvt_body.html"><span class="doc">fix nvt_body</span></a>, <a class="reference internal" href="fix_npt_body.html"><span class="doc">fix npt_body</span></a>, <a class="reference internal" href="fix_modify.html"><span class="doc">fix_modify</span></a></p>
<p><strong>Default:</strong> none</p>
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