<p>See the supporting information of <a class="reference internal" href="#brennan"><span class="std std-ref">(Brennan)</span></a> or the
publication by <a class="reference internal" href="#moore"><span class="std std-ref">(Moore)</span></a> for more details on the functional
form.</p>
<p>An interpolation table is used to evaluate the density-dependent
energy (Integral(A(rho)drho) and force (A(rho)). Note that the
pre-factor to the energy is computed after the interpolation, thus the
Integral(A(rho)drho will have units of energy / length^4.</p>
<p>The interpolation table is created as a pre-computation by fitting
cubic splines to the file values and interpolating the
density-dependent energy and force at each of <em>N</em> densities. During a
simulation, the tables are used to interpolate the density-dependent
energy and force as needed for each pair of particles separated by a
distance <em>R</em>. The interpolation is done in one of 2 styles: <em>lookup</em>
and <em>linear</em>.</p>
<p>For the <em>lookup</em> style, the density is used to find the nearest table
entry, which is the density-dependent energy and force.</p>
<p>For the <em>linear</em> style, the density is used to find the 2 surrounding
table values from which the density-dependent energy and force are
computed by linear interpolation.</p>
<p>The following coefficients must be defined for each pair of atoms
types via the <a class="reference internal" href="pair_coeff.html"><span class="doc">pair_coeff</span></a> command as in the examples
above.</p>
<ul class="simple">
<li>filename</li>
<li>keyword</li>
<li>species1</li>
<li>species2</li>
<li>cutoff (distance units)</li>
</ul>
<p>The filename specifies a file containing the tabulated
density-dependent energy and force. The keyword specifies a section
of the file. The cutoff is an optional coefficient. If not
specified, the outer cutoff in the table itself (see below) will be
used to build an interpolation table that extend to the largest
tabulated distance. If specified, only file values up to the cutoff
are used to create the interpolation table. The format of this file
is described below.</p>
<p>The species tags define the site-site interaction potential between
two species contained within two different particles. The species
tags must either correspond to the species defined in the reaction
kinetics files specified with the <a class="reference internal" href="fix_rx.html"><span class="doc">fix rx</span></a> command or they
must correspond to the tag “1fluid”, signifying interaction with a
product species mixture determined through a one-fluid approximation.
The interaction potential is weighted by the geometric average of the
concentrations of the two species. The coarse-grained potential is
stored before and after the reaction kinetics solver is applied, where
the difference is defined to be the internal chemical energy (uChem).</p>
<hr class="docutils" />
<p>The format of a tabulated file is a series of one or more sections,
defined as follows (without the parenthesized comments):</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1"># Density-dependent function (one or more comment or blank lines)</span>
<p>This command is part of the USER-DPD package. It is only enabled if
LAMMPS was built with that package. See the <a class="reference internal" href="Section_start.html#start-3"><span class="std std-ref">Making LAMMPS</span></a> section for more info.</p>
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