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<title>pair_style line/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 line/lj command</li>
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<div class="section" id="pair-style-line-lj-command">
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<span id="index-0"></span><h1>pair_style line/lj command<a class="headerlink" href="#pair-style-line-lj-command" title="Permalink to this headline">¶</a></h1>
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<div class="section" id="pair-style-line-lj-omp-command">
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<h1>pair_style line/lj/omp command<a class="headerlink" href="#pair-style-line-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 line/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 line/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>line/lj</em> treats particles which are line segments as a set of
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small spherical particles that tile the line segment length as
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explained below. Interactions between two line segments, each with N1
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and N2 spherical particles, are calculated as the pairwise sum of
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N1*N2 Lennard-Jones interactions. Interactions between a line segment
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with N spherical particles and a point particle are treated as the
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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
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interactions.</p>
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<p>The cutoff distance for an interaction between 2 line segments, or
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between a line segment and a point particle, is calculated from the
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position of the line segment (its center), not between pairs of
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individual spheres comprising the line segment. Thus an interaction
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is either calculated in its entirety or not at all.</p>
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<p>The set of non-overlapping spherical particles that represent a line
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segment, for purposes of this pair style, are generated in the
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following manner. Their size is a function of the line segment length
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and the specified sigma for that particle type. If a line segment has
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a length L and is of type I, then the number of spheres N that
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represent the segment is calculated as N = L/sigma_II, rounded up to
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an integer value. Thus if L is not evenly divisibly by sigam_II, N is
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incremented to include one extra sphere. In this case, the spheres
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must be slightly smaller than sigma_II so as not to overlap, so a new
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sigma-prime is chosen as the sphere diameter, such that L/N =
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sigma-prime. Thus the line segment interacts with other segments or
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point particles as a collection of N spheres of diameter sigma-prime,
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evenly spaced along the line segment, so as to exactly cover its
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length.</p>
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<p>The LJ interaction between 2 spheres on different line segments of
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types I,J is computed with an arithmetic mixing of the sigma values of
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the 2 spheres and using the specified epsilon value for I,J atom
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types. Note that because the sigma values for line segment spheres is
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computed using only sigma_II values, specific to the line segment’s
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type, this means that any specified sigma_IJ values (for I != J) are
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effectively ignored.</p>
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<p>For style <em>line/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 line segments so they participate in
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line/line or line/particle interactions requires the use the
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<a class="reference internal" href="atom_style.html"><em>atom_style line</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_tri_lj.html"><em>pair_style tri/lj</em></a></p>
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<p><strong>Default:</strong> none</p>
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