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<div class="section" id="compute-com-command">
<span id="index-0"></span><h1>compute com command<a class="headerlink" href="#compute-com-command" title="Permalink to this headline">¶</a></h1>
<div class="section" id="syntax">
<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline">¶</a></h2>
<div class="highlight-python"><div class="highlight"><pre>compute ID group-ID com general_keyword general_values
</pre></div>
</div>
<ul class="simple">
<li>ID, group-ID are documented in <a class="reference internal" href="compute.html"><em>compute</em></a> command</li>
<li>com = style name of this compute command</li>
<li>general_keywords general_values are documented in <a class="reference external" href="compute.html"">compute</a></li>
</ul>
</div>
<div class="section" id="examples">
<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
<div class="highlight-python"><div class="highlight"><pre>compute 1 all com
</pre></div>
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<div class="section" id="description">
<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
<p>Define a computation that calculates the center-of-mass of the group
of atoms, including all effects due to atoms passing thru periodic
boundaries.</p>
<p>A vector of three quantites is calculated by this compute, which
are the x,y,z coordinates of the center of mass.</p>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p class="last">The coordinates of an atom contribute to the
center-of-mass in “unwrapped” form, by using the image flags
associated with each atom. See the <a class="reference internal" href="dump.html"><em>dump custom</em></a> command
for a discussion of “unwrapped” coordinates. See the Atoms section of
the <a class="reference internal" href="read_data.html"><em>read_data</em></a> command for a discussion of image flags
and how they are set for each atom. You can reset the image flags
(e.g. to 0) before invoking this compute by using the <a class="reference internal" href="set.html"><em>set image</em></a> command.</p>
</div>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p class="last">If an atom is part of a rigid body (see the <a class="reference internal" href="fix_rigid.html"><em>fix rigid</em></a> command), it’s periodic image flags are altered,
and its contribution to the center-of-mass may not reflect its true
contribution. See the <a class="reference internal" href="fix_rigid.html"><em>fix rigid</em></a> command for details.
Thus, to compute the center-of-mass of rigid bodies as they cross
periodic boundaries, you will need to post-process a <a class="reference internal" href="dump.html"><em>dump file</em></a> containing coordinates of the atoms in the bodies.</p>
</div>
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<div class="section" id="output-info">
<h2>Output info<a class="headerlink" href="#output-info" title="Permalink to this headline">¶</a></h2>
<p>This compute calculates a global vector of length 3, which can be
accessed by indices 1-3 by any command that uses global vector values
from a compute as input. See <span class="xref std std-ref">this section</span> for an overview of LIGGGHTS(R)-PUBLIC output
options.</p>
<p>The vector values are “intensive”. The vector values will be in
distance <a class="reference internal" href="units.html"><em>units</em></a>.</p>
</div>
<div class="section" id="restrictions">
<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
<blockquote>
<div>none</div></blockquote>
</div>
<div class="section" id="related-commands">
<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
<p><a class="reference internal" href="compute_com_molecule.html"><em>compute com/molecule</em></a></p>
<p><strong>Default:</strong> none</p>
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