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<div class="section" id="compute-pe-command">
<span id="index-0"></span><h1>compute pe command</h1>
<div class="section" id="syntax">
<h2>Syntax</h2>
<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">pe</span> <span class="n">keyword</span> <span class="o">...</span>
</pre></div>
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<ul class="simple">
<li>ID, group-ID are documented in <a class="reference internal" href="compute.html"><span class="doc">compute</span></a> command</li>
<li>pe = style name of this compute command</li>
<li>zero or more keywords may be appended</li>
<li>keyword = <em>pair</em> or <em>bond</em> or <em>angle</em> or <em>dihedral</em> or <em>improper</em> or <em>kspace</em></li>
</ul>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">compute</span> <span class="mi">1</span> <span class="nb">all</span> <span class="n">pe</span>
<span class="n">compute</span> <span class="n">molPE</span> <span class="nb">all</span> <span class="n">pe</span> <span class="n">bond</span> <span class="n">angle</span> <span class="n">dihedral</span> <span class="n">improper</span>
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>Define a computation that calculates the potential energy of the
entire system of atoms. The specified group must be &#8220;all&#8221;. See the
<a class="reference internal" href="compute_pe_atom.html"><span class="doc">compute pe/atom</span></a> command if you want per-atom
energies. These per-atom values could be summed for a group of atoms
via the <a class="reference internal" href="compute_reduce.html"><span class="doc">compute reduce</span></a> command.</p>
<p>The energy is calculated by the various pair, bond, etc potentials
defined for the simulation. If no extra keywords are listed, then the
potential energy is the sum of pair, bond, angle, dihedral, improper,
and kspace (long-range) energy. If any extra keywords are listed,
then only those components are summed to compute the potential energy.</p>
<p>The Kspace contribution requires 1 extra FFT each timestep the energy
is calculated, if using the PPPM solver via the <a class="reference internal" href="kspace_style.html"><span class="doc">kspace_style pppm</span></a> command. Thus it can increase the cost of the
PPPM calculation if it is needed on a large fraction of the simulation
timesteps.</p>
<p>Various fixes can contribute to the total potential energy of the
system. See the doc pages for <a class="reference internal" href="fix.html"><span class="doc">individual fixes</span></a> for
details. The <em>thermo</em> option of the
<a class="reference internal" href="compute_modify.html"><span class="doc">compute_modify</span></a> command determines whether these
contributions are added into the computed potential energy. If no
keywords are specified the default is <em>yes</em>. If any keywords are
specified, the default is <em>no</em>.</p>
<p>A compute of this style with the ID of &#8220;thermo_pe&#8221; is created when
LAMMPS starts up, as if this command were in the input script:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">compute</span> <span class="n">thermo_pe</span> <span class="nb">all</span> <span class="n">pe</span>
</pre></div>
</div>
<p>See the &#8220;thermo_style&#8221; command for more details.</p>
<hr class="docutils" />
<p><strong>Output info:</strong></p>
<p>This compute calculates a global scalar (the potential energy). This
value can be used by any command that uses a global scalar value from
a compute as input. See <a class="reference internal" href="Section_howto.html#howto-15"><span class="std std-ref">Section_howto 15</span></a> for an overview of LAMMPS output
options.</p>
<p>The scalar value calculated by this compute is &#8220;extensive&#8221;. The
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scalar value will be in energy <a class="reference internal" href="units.html"><span class="doc">units</span></a>.</p>
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</div>
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<blockquote>
<div>none</div></blockquote>
</div>
<div class="section" id="related-commands">
<h2>Related commands</h2>
<p><a class="reference internal" href="compute_pe_atom.html"><span class="doc">compute pe/atom</span></a></p>
<p><strong>Default:</strong> none</p>
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