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<div class="section" id="pair-style-body-rounded-polygon-command">
<span id="index-0"></span><h1>pair_style body/rounded/polygon command<a class="headerlink" href="#pair-style-body-rounded-polygon-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>pair_style body/rounded/polygon cutoff_global cutoff_inner delta_ua c_n
</pre></div>
</div>
<ul class="simple">
<li>cutoff_global = global cutoff for COM interactions (distance units)</li>
<li>cutoff_inner = cutoff for vertex-vertex and vertex-edge interactions (distance units)</li>
<li>delta_ua = characteristic contact length (distance units)</li>
<li>c_n = normal friction coefficient (energy time/distance^2)</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>pair_style body/rounded/polygon 6.0 0.5 0.5 0.1
pair_coeff 1 1 1.0 100.0 12.0
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
<p>Style <em>body/rounded/polygon</em> implements the pairwise body/body
interactions between 2D convex polygons, as described
in <a class="reference internal" href="#fraige"><span>Fraige</span></a>. This pair style is designed for use with
the &#8220;rounded/polygon&#8221; body style, which is specified as
an argument to the &#8220;atom-style body/rounded/polygon&#8221; command.
See the <a class="reference internal" href="body.html"><em>body</em></a> doc page for more details about the body
styles LAMMPS supports.</p>
<p>The &#8220;rounded/polygon&#8221; style treats a body particle as a discrete
element model (DEM) polygon composed of N vertices.
The coordinates of a body particle are its center-of-mass (COM).
The initial position of the vertices are specified the data file.
The current implementation follows the multiple contact points model as
described in <a class="reference internal" href="#fraige"><span>Fraige</span></a>, but neglects and the contact history
the tangential contact forces for now.</p>
<p>The parameters <em>delta_ua</em> and <em>c_n</em> are the characteristic contact length
and the normal friction coefficient, respectively. See Eqs. (1) and (5)
in <a class="reference internal" href="#fraige"><span>Fraige</span></a> for more details.</p>
<p>For style <em>body/rounded/polygon</em>, the following coefficients
must be defined for each pair of atoms types via the <a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></a>
command as in the examples above:</p>
<ul class="simple">
<li>sigma = vertex rounded diameter (distance units)</li>
<li>k_n = normal repulsion strength (energy/distance^2)</li>
<li>k_na = normal attraction strength (energy/distance^2)</li>
<li>cutoff = cutoff for COM interactions (distance units)</li>
</ul>
<p>The last parameter is optional. If not specified, the global
cutoff specified in the pair_style command is used.</p>
<p>Note that the current implementation assumes that the edge length
of the polygons (L) should be at least twice greater than
the vertex rounded radius (sigma) so as to distinguish vertex-vertex from
vertex-edge contacts.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Because this pair style requires the body velocities to compute
the friction component of the forces, users should specify
<em>comm_modify vel yes</em> in the input script with this pair style.</p>
</div>
<hr class="docutils" />
<p><strong>Mixing, shift, table, tail correction, restart, rRESPA info</strong>:</p>
<p>For atom type pairs I,J and I != J, the epsilon and sigma coefficients
and cutoff distance for all of this pair style can be mixed. The
default mix value is <em>geometric</em>. See the &#8220;pair_modify&#8221; command for
details.</p>
<p>This pair style does not support the <a class="reference internal" href="pair_modify.html"><em>pair_modify</em></a>
shift, table, and tail options.</p>
<p>This pair style does not write its information to <a class="reference internal" href="restart.html"><em>binary restart files</em></a>.</p>
<p>This pair style can only be used via the <em>pair</em> keyword of the
<a class="reference internal" href="run_style.html"><em>run_style respa</em></a> command. It does not support the
<em>inner</em>, <em>middle</em>, <em>outer</em> keywords.</p>
</div>
<hr class="docutils" />
<div class="section" id="restrictions">
<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
<p>This style is part of the BODY package. It is only enabled if LAMMPS
was built with that package. See the <span class="xref std std-ref">Making LAMMPS</span> section for more info.</p>
<p>Defining particles to be bodies so they participate in body/body or
body/particle interactions requires the use of the <a class="reference internal" href="atom_style.html"><em>atom_style body</em></a> command.</p>
</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="pair_coeff.html"><em>pair_coeff</em></a></p>
<p><strong>Default:</strong> none</p>
<p id="fraige"><strong>(Fraige)</strong> F. Y. Fraige, P. A. Langston, A. J. Matchett, J. Dodds,
Particuology, 6, 455 (2008).</p>
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