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<title>pair_style tri/lj command — LAMMPS 15 May 2015 version documentation</title>
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<li class="toctree-l1"><a class="reference internal" href="Section_intro.html">1. Introduction</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_accelerate.html">5. Accelerating LAMMPS performance</a></li>
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<li>pair_style tri/lj command</li>
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<div class="section" id="pair-style-tri-lj-command">
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<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>
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</div>
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<div class="section" id="pair-style-tri-lj-omp-command">
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<h1>pair_style tri/lj/omp command<a class="headerlink" href="#pair-style-tri-lj-omp-command" title="Permalink to this headline">¶</a></h1>
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<div class="section" id="syntax">
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<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>pair_style tri/lj cutoff
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</pre></div>
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</div>
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<p>cutoff = global cutoff for interactions (distance units)</p>
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</div>
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<div class="section" id="examples">
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<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>pair_style tri/lj 3.0
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pair_coeff * * 1.0 1.0
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pair_coeff 1 1 1.0 1.5 2.5
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</pre></div>
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</div>
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</div>
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<div class="section" id="description">
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<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
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<p>Style <em>tri/lj</em> treats particles which are triangles as a set of small
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spherical particles that tile the triangle surface as explained below.
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Interactions between two triangles, each with N1 and N2 spherical
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particles, are calculated as the pairwise sum of N1*N2 Lennard-Jones
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interactions. Interactions between a triangle with N spherical
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particles and a point particle are treated as the pairwise sum of N
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Lennard-Jones interactions. See the <a class="reference internal" href="pair_lj.html"><em>pair_style lj/cut</em></a>
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doc page for the definition of Lennard-Jones interactions.</p>
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<p>The cutoff distance for an interaction between 2 triangles, or between
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a triangle and a point particle, is calculated from the position of
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the triangle (its centroid), not between pairs of individual spheres
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comprising the triangle. Thus an interaction is either calculated in
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its entirety or not at all.</p>
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<p>The set of non-overlapping spherical particles that represent a
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triangle, for purposes of this pair style, are generated in the
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following manner. Assume the triangle is of type I, and sigma_II has
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been specified. We want a set of spheres with centers in the plane of
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the triangle, none of them larger in diameter than sigma_II, which
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completely cover the triangle’s area, but with minimial overlap and a
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minimal total number of spheres. This is done in a recursive manner.
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Place a sphere at the centroid of the original triangle. Calculate
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what diameter it must have to just cover all 3 corner points of the
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triangle. If that diameter is equal to or smaller than sigma_II, then
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include a sphere of the calculated diameter in the set of covering
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spheres. It the diameter is larger than sigma_II, then split the
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triangle into 2 triangles by bisecting its longest side. Repeat the
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process on each sub-triangle, recursing as far as needed to generate a
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set of covering spheres. When finished, the original criteria are
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met, and the set of covering spheres shoule be near minimal in number
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and overlap, at least for input triangles with a reasonable
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aspect-ratio.</p>
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<p>The LJ interaction between 2 spheres on different triangles of types
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I,J is computed with an arithmetic mixing of the sigma values of the 2
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spheres and using the specified epsilon value for I,J atom types.
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Note that because the sigma values for triangles spheres is computed
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using only sigma_II values, specific to the triangles’s type, this
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means that any specified sigma_IJ values (for I != J) are effectively
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ignored.</p>
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<p>For style <em>tri/lj</em>, the following coefficients must be defined for
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each pair of atoms types via the <a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></a> command
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as in the examples above, or in the data file or restart files read by
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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>
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commands:</p>
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<ul class="simple">
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<li>epsilon (energy units)</li>
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<li>sigma (distance units)</li>
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<li>cutoff (distance units)</li>
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</ul>
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<p>The last coefficient is optional. If not specified, the global cutoff
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is used.</p>
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<hr class="docutils" />
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<p>Styles with a <em>cuda</em>, <em>gpu</em>, <em>intel</em>, <em>kk</em>, <em>omp</em>, or <em>opt</em> suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed in <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></a>
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.</p>
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<p>These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
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KOKKOS, USER-OMP and OPT packages, respectively. They are only
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enabled if LAMMPS was built with those packages. See the <a class="reference internal" href="Section_start.html#start-3"><span>Making LAMMPS</span></a> section for more info.</p>
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<p>You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the <a class="reference internal" href="Section_start.html#start-7"><span>-suffix command-line switch</span></a> when you invoke LAMMPS, or you can
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use the <a class="reference internal" href="suffix.html"><em>suffix</em></a> command in your input script.</p>
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<p>See <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></a> of the manual for
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more instructions on how to use the accelerated styles effectively.</p>
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<hr class="docutils" />
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<p><strong>Mixing, shift, table, tail correction, restart, rRESPA info</strong>:</p>
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<p>For atom type pairs I,J and I != J, the epsilon and sigma coefficients
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and cutoff distance for all of this pair style can be mixed. The
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default mix value is <em>geometric</em>. See the “pair_modify” command for
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details.</p>
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<p>This pair style does not support the <a class="reference internal" href="pair_modify.html"><em>pair_modify</em></a>
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shift, table, and tail options.</p>
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<p>This pair style does not write its information to <a class="reference internal" href="restart.html"><em>binary restart files</em></a>.</p>
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<p>This pair style can only be used via the <em>pair</em> keyword of the
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<a class="reference internal" href="run_style.html"><em>run_style respa</em></a> command. It does not support the
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<em>inner</em>, <em>middle</em>, <em>outer</em> keywords.</p>
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</div>
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<hr class="docutils" />
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<div class="section" id="restrictions">
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<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
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<p>This style is part of the ASPHERE package. It is only enabled if
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LAMMPS was built with that package. See the <span class="xref std std-ref">Making LAMMPS</span> section for more info.</p>
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<p>Defining particles to be triangles so they participate in tri/tri or
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tri/particle interactions requires the use the <a class="reference internal" href="atom_style.html"><em>atom_style tri</em></a> command.</p>
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</div>
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<div class="section" id="related-commands">
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<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
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<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>
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<p><strong>Default:</strong> none</p>
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