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<div class="section" id="compute-pair-command">
<span id="index-0"></span><h1>compute pair 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">pair</span> <span class="n">pstyle</span> <span class="n">evalue</span>
</pre></div>
</div>
<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>pair = style name of this compute command</li>
<li>pstyle = style name of a pair style that calculates additional values</li>
<li>evalue = <em>epair</em> or <em>evdwl</em> or <em>ecoul</em> or blank (optional setting)</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">pair</span> <span class="n">gauss</span>
<span class="n">compute</span> <span class="mi">1</span> <span class="nb">all</span> <span class="n">pair</span> <span class="n">lj</span><span class="o">/</span><span class="n">cut</span><span class="o">/</span><span class="n">coul</span><span class="o">/</span><span class="n">cut</span> <span class="n">ecoul</span>
<span class="n">compute</span> <span class="mi">1</span> <span class="nb">all</span> <span class="n">pair</span> <span class="n">reax</span>
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>Define a computation that extracts additional values calculated by a
pair style, and makes them accessible for output or further processing
by other commands. The group specified for this command is ignored.</p>
<p>The specified <em>pstyle</em> must be a pair style used in your simulation
either by itself or as a sub-style in a <a class="reference internal" href="pair_hybrid.html"><span class="doc">pair_style hybrid or hybrid/overlay</span></a> command.</p>
<p>The <em>evalue</em> setting is optional; it may be left off the command. All
pair styles tally a potential energy <em>epair</em> which may be broken into
two parts: <em>evdwl</em> and <em>ecoul</em> such that <em>epair</em> = <em>evdwl</em> + <em>ecoul</em>.
If the pair style calculates Coulombic interactions, their energy will
be tallied in <em>ecoul</em>. Everything else (whether it is a Lennard-Jones
style van der Waals interaction or not) is tallied in <em>evdwl</em>. If
<em>evalue</em> is specified as <em>epair</em> or left out, then <em>epair</em> is stored
as a global scalar by this compute. This is useful when using
<a class="reference internal" href="pair_hybrid.html"><span class="doc">pair_style hybrid</span></a> if you want to know the portion
of the total energy contributed by one sub-style. If <em>evalue</em> is
specfied as <em>evdwl</em> or <em>ecoul</em>, then just that portion of the energy
is stored as a global scalar.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The energy returned by the <em>evdwl</em> keyword does not include tail
corrections, even if they are enabled via the
<a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> command.</p>
</div>
<p>Some pair styles tally additional quantities, e.g. a breakdown of
potential energy into a dozen or so components is tallied by the
<a class="reference internal" href="pair_reax.html"><span class="doc">pair_style reax</span></a> commmand. These values (1 or more)
are stored as a global vector by this compute. See the doc page for
<a class="reference internal" href="pair_style.html"><span class="doc">individual pair styles</span></a> for info on these values.</p>
<p><strong>Output info:</strong></p>
<p>This compute calculates a global scalar which is <em>epair</em> or <em>evdwl</em> or
<em>ecoul</em>. If the pair style supports it, it also calculates a global
vector of length &gt;= 1, as determined by the pair style. These values
can be used by any command that uses global scalar or vector values
from a compute as input. See <a class="reference internal" href="Section_howto.html#howto-15"><span class="std std-ref">this section</span></a> for an overview of LAMMPS output
options.</p>
<p>The scalar and vector values calculated by this compute are
&#8220;extensive&#8221;.</p>
<p>The scalar value will be in energy <a class="reference internal" href="units.html"><span class="doc">units</span></a>. The vector
values will typically also be in energy <a class="reference internal" href="units.html"><span class="doc">units</span></a>, but see
the doc page for the pair style for details.</p>
</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.html"><span class="doc">compute pe</span></a>, <a class="reference internal" href="compute_bond.html"><span class="doc">compute bond</span></a></p>
</div>
<div class="section" id="default">
<h2>Default</h2>
<p>The default for <em>evalue</em> is <em>epair</em>.</p>
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