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<div class="section" id="compute-dilatation-atom-command">
<span id="index-0"></span><h1>compute dilatation/atom 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">dilatation</span><span class="o">/</span><span class="n">atom</span>
</pre></div>
</div>
<ul class="simple">
<li>ID, group-ID are documented in compute command</li>
<li>dilation/atom = style name of this compute command</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">dilatation</span><span class="o">/</span><span class="n">atom</span>
</pre></div>
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</div>
<div class="section" id="description">
<h2>Description</h2>
<p>Define a computation that calculates the per-atom dilatation for each
atom in a group. This is a quantity relevant for <a class="reference internal" href="pair_peri.html"><span class="doc">Peridynamics models</span></a>. See <a class="reference external" href="PDF/PDLammps_overview.pdf">this document</a>
for an overview of LAMMPS commands for Peridynamics modeling.</p>
<p>For small deformation, dilatation of is the measure of the volumetric
strain.</p>
<p>The dilatation &#8220;theta&#8221; for each peridynamic particle I is calculated
as a sum over its neighbors with unbroken bonds, where the
contribution of the IJ pair is a function of the change in bond length
(versus the initial length in the reference state), the volume
fraction of the particles and an influence function. See the
<a class="reference external" href="http://www.sandia.gov/~mlparks/papers/PDLAMMPS.pdf">PDLAMMPS user guide</a> for a formal
definition of dilatation.</p>
<p>This command can only be used with a subset of the Peridynamic <a class="reference internal" href="pair_peri.html"><span class="doc">pair styles</span></a>: peri/lps, peri/ves and peri/eps.</p>
<p>The dilatation value will be 0.0 for atoms not in the specified
compute group.</p>
<p><strong>Output info:</strong></p>
<p>This compute calculates a per-atom vector, which can be accessed by
any command that uses per-atom values from a compute as input. See
Section_howto 15 for an overview of LAMMPS output options.</p>
<p>The per-atom vector values are unitlesss numbers (theta) &gt;= 0.0.</p>
</div>
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<p>This compute is part of the PERI 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>
</div>
<div class="section" id="related-commands">
<h2>Related commands</h2>
<p><a class="reference internal" href="compute_damage_atom.html"><span class="doc">compute damage/atom</span></a>,
<a class="reference internal" href="compute_plasticity_atom.html"><span class="doc">compute plasticity/atom</span></a></p>
<p><strong>Default:</strong> none</p>
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