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<title>pair_write command — LAMMPS 15 May 2015 version documentation</title>
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<li>pair_write command</li>
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<div class="section" id="pair-write-command">
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<span id="index-0"></span><h1>pair_write command<a class="headerlink" href="#pair-write-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_write itype jtype N style inner outer file keyword Qi Qj
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</pre></div>
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</div>
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<ul class="simple">
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<li>itype,jtype = 2 atom types</li>
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<li>N = # of values</li>
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<li>style = <em>r</em> or <em>rsq</em> or <em>bitmap</em></li>
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<li>inner,outer = inner and outer cutoff (distance units)</li>
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<li>file = name of file to write values to</li>
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<li>keyword = section name in file for this set of tabulated values</li>
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<li>Qi,Qj = 2 atom charges (charge units) (optional)</li>
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</ul>
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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_write 1 3 500 r 1.0 10.0 table.txt LJ
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pair_write 1 1 1000 rsq 2.0 8.0 table.txt Yukawa_1_1 -0.5 0.5
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</pre></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>Write energy and force values to a file as a function of distance for
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the currently defined pair potential. This is useful for plotting the
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potential function or otherwise debugging its values. If the file
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already exists, the table of values is appended to the end of the file
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to allow multiple tables of energy and force to be included in one
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file.</p>
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<p>The energy and force values are computed at distances from inner to
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outer for 2 interacting atoms of type itype and jtype, using the
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appropriate <a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></a> coefficients. If the style
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is <em>r</em>, then N distances are used, evenly spaced in r; if the style is
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<em>rsq</em>, N distances are used, evenly spaced in r^2.</p>
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<p>For example, for N = 7, style = <em>r</em>, inner = 1.0, and outer = 4.0,
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values are computed at r = 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0.</p>
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<p>If the style is <em>bitmap</em>, then 2^N values are written to the file in a
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format and order consistent with how they are read in by the
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<a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></a> command for pair style <em>table</em>. For
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reasonable accuracy in a bitmapped table, choose N >= 12, an <em>inner</em>
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value that is smaller than the distance of closest approach of 2
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atoms, and an <em>outer</em> value <= cutoff of the potential.</p>
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<p>If the pair potential is computed between charged atoms, the charges
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of the pair of interacting atoms can optionally be specified. If not
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specified, values of Qi = Qj = 1.0 are used.</p>
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<p>The file is written in the format used as input for the
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<a class="reference internal" href="pair_style.html"><em>pair_style</em></a> <em>table</em> option with <em>keyword</em> as the
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section name. Each line written to the file lists an index number
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(1-N), a distance (in distance units), an energy (in energy units),
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and a force (in force units).</p>
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</div>
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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>All force field coefficients for pair and other kinds of interactions
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must be set before this command can be invoked.</p>
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<p>Due to how the pairwise force is computed, an inner value > 0.0 must
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be specified even if the potential has a finite value at r = 0.0.</p>
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<p>For EAM potentials, the pair_write command only tabulates the
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pairwise portion of the potential, not the embedding portion.</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_style.html"><em>pair_style</em></a>, <a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></a></p>
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<p><strong>Default:</strong> none</p>
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