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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="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 1.0 0.8 1.12
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pair_coeff 1 2 1.0 2.0 1.0 1.5 1.12 5.0
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pair_coeff 1 2 1.0 0.0 1.0 1.0 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 set of non-overlapping spherical sub-particles that represent a
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line segment are generated in the following manner. Their size is a
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function of the line segment length and the specified sub-particle
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size for that particle type. If a line segment has a length L and is
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of type I, then the number of spheres N that represent the segment is
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calculated as N = L/sizeI, rounded up to an integer value. Thus if L
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is not evenly divisibly by sizeI, N is incremented to include one
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extra sphere. The centers of the spheres are spaced equally along the
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line segment. Imagine N+1 equally-space points, which include the 2
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end points of the segment. The sphere centers are halfway between
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each pair of points.</p>
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<p>The LJ interaction between 2 spheres on different line segments (or a
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sphere on a line segment and a point particles) is computed with
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sub-particle epsilon, sigma, and cutoff values that are set by the
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pair_coeff command, as described below. If the distance bewteen the 2
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spheres is greater than the sub-particle cutoff, there is no
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interaction. This means that some pairs of sub-particles on 2 line
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segments may interact, but others may not.</p>
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<p>For purposes of creating the neighbor list for pairs of interacting
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line segments or lines/point particles, a regular particle-particle
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cutoff is used, as defined by the <em>cutoff</em> setting above in the
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pair_style command or overridden with an optional argument in the
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pair_coeff command for a type pair as discussed below. The distance
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between the centers of 2 line segments, or the center of a line
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segment and a point particle, must be less than this distance (plus
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the neighbor skin; see the <a class="reference external" href="neighbor">neighbor</a> command), for the pair
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of particles to be included in the neighbor list.</p>
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<div class="admonition note">
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<p class="first admonition-title">Note</p>
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<p class="last">This means that a too-short value for the <em>cutoff</em> setting can
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exclude a pair of particles from the neighbor list even if pairs of
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their sub-particle spheres would interact, based on the sub-particle
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cutoff specified in the pair_coeff command. E.g. sub-particles at the
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ends of the line segments that are close to each other. Which may not
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be what you want, since it means the ends of 2 line segments could
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pass through each other. It is up to you to specify a <em>cutoff</em>
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setting that is consistent with the length of the line segments you
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are using and the sub-particle cutoff settings.</p>
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</div>
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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 atom 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>sizeI (distance units)</li>
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<li>sizeJ (distance units)</li>
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<li>epsilon (energy units)</li>
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<li>sigma (distance units)</li>
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<li>subcutoff (distance units)</li>
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<li>cutoff (distance units)</li>
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</ul>
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<p>The <em>sizeI</em> and <em>sizeJ</em> coefficients are the sub-particle sizes for
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line particles of type I and type J. They are used to define the N
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sub-particles per segment as described above. These coefficients are
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actually stored on a per-type basis. Thus if there are multiple
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pair_coeff commmands that involve type I, as either the first or
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second atom type, you should use consistent values for sizeI or sizeJ
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in all of them. If you do not do this, the last value specified for
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sizeI will apply to all segments of type I. If typeI or typeJ refers
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to point particles, the corresponding sizeI or sizeJ is ignored; it
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can be set to 0.0.</p>
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<p>The <em>epsilon</em>, <em>sigma</em>, and <em>subcutoff</em> coefficients are used to
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compute an LJ interactions between a pair of sub-particles on 2 line
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segments (of type I and J), or between a sub particle/point particle
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pair. As discussed above, the <em>subcutoff</em> and <em>cutoff</em> params are
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different. The latter is only used for building the neighbor list
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when the distance between centers of two line segments or one segment
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and a point particle is calculated.</p>
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<p>The <em>cutoff</em> coefficient is optional. If not specified, the global
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cutoff is used.</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, coeffiecients must be specified.
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No default mixing rules are used.</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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