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<div class="section" id="pair-style-tri-lj-command">
<span id="index-0"></span><h1>pair_style tri/lj command<a class="headerlink" href="#pair-style-tri-lj-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 tri/lj cutoff
</pre></div>
</div>
<p>cutoff = global cutoff for interactions (distance units)</p>
</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 tri/lj 3.0
pair_coeff * * 1.0 1.0
pair_coeff 1 1 1.0 1.5 2.5
</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>tri/lj</em> treats particles which are triangles as a set of small
spherical particles that tile the triangle surface as explained below.
Interactions between two triangles, each with N1 and N2 spherical
particles, are calculated as the pairwise sum of N1*N2 Lennard-Jones
interactions. Interactions between a triangle with N spherical
particles and a point particle are treated as the pairwise sum of N
Lennard-Jones interactions. See the <a class="reference internal" href="pair_lj.html"><em>pair_style lj/cut</em></a>
doc page for the definition of Lennard-Jones interactions.</p>
<p>The cutoff distance for an interaction between 2 triangles, or between
a triangle and a point particle, is calculated from the position of
the triangle (its centroid), not between pairs of individual spheres
comprising the triangle. Thus an interaction is either calculated in
its entirety or not at all.</p>
<p>The set of non-overlapping spherical particles that represent a
triangle, for purposes of this pair style, are generated in the
following manner. Assume the triangle is of type I, and sigma_II has
been specified. We want a set of spheres with centers in the plane of
the triangle, none of them larger in diameter than sigma_II, which
completely cover the triangle&#8217;s area, but with minimial overlap and a
minimal total number of spheres. This is done in a recursive manner.
Place a sphere at the centroid of the original triangle. Calculate
what diameter it must have to just cover all 3 corner points of the
triangle. If that diameter is equal to or smaller than sigma_II, then
include a sphere of the calculated diameter in the set of covering
spheres. It the diameter is larger than sigma_II, then split the
triangle into 2 triangles by bisecting its longest side. Repeat the
process on each sub-triangle, recursing as far as needed to generate a
set of covering spheres. When finished, the original criteria are
met, and the set of covering spheres shoule be near minimal in number
and overlap, at least for input triangles with a reasonable
aspect-ratio.</p>
<p>The LJ interaction between 2 spheres on different triangles of types
I,J is computed with an arithmetic mixing of the sigma values of the 2
spheres and using the specified epsilon value for I,J atom types.
Note that because the sigma values for triangles spheres is computed
using only sigma_II values, specific to the triangles&#8217;s type, this
means that any specified sigma_IJ values (for I != J) are effectively
ignored.</p>
<p>For style <em>tri/lj</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, or in the data file or restart files read by
the <a class="reference internal" href="read_data.html"><em>read_data</em></a> or <a class="reference internal" href="read_restart.html"><em>read_restart</em></a>
commands:</p>
<ul class="simple">
<li>epsilon (energy units)</li>
<li>sigma (distance units)</li>
<li>cutoff (distance units)</li>
</ul>
<p>The last coefficient is optional. If not specified, the global cutoff
is used.</p>
<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 ASPHERE 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 triangles so they participate in tri/tri or
tri/particle interactions requires the use the <a class="reference internal" href="atom_style.html"><em>atom_style tri</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>, <a class="reference internal" href="pair_line_lj.html"><em>pair_style line/lj</em></a></p>
<p><strong>Default:</strong> none</p>
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