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<div class="section" id="pair-style-exp6-rx-command">
<span id="index-0"></span><h1>pair_style exp6/rx command</h1>
<div class="section" id="syntax">
<h2>Syntax</h2>
<pre class="literal-block">
pair_style exp6/rx cutoff
</pre>
<ul class="simple">
<li>cutoff = global cutoff for DPD interactions (distance units)</li>
</ul>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<pre class="literal-block">
pair_style exp6/rx 10.0
pair_coeff * * exp6.params h2o h2o 1.0 1.0 10.0
pair_coeff * * exp6.params h2o 1fluid 1.0 1.0 10.0
pair_coeff * * exp6.params 1fluid 1fluid 1.0 1.0 10.0
</pre>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>Style <em>exp6/rx</em> is used in reaction DPD simulations, where the
coarse-grained (CG) particles are composed of <em>m</em> species whose
reaction rate kinetics are determined from a set of <em>n</em> reaction rate
equations through the <a class="reference internal" href="fix_rx.html"><span class="doc">fix rx</span></a> command. The species of
one CG particle can interact with a species in a neighboring CG
particle through a site-site interaction potential model. The
<em>exp6/rx</em> style computes an exponential-6 potential given by</p>
<img alt="_images/pair_exp6_rx.jpg" class="align-center" src="_images/pair_exp6_rx.jpg" />
<p>where the <em>epsilon</em> parameter determines the depth of the potential
minimum located at <em>Rm</em>, and <em>alpha</em> determines the softness of the repulsion.</p>
<p>The coefficients must be defined for each species in a given particle
type via the <a class="reference internal" href="pair_coeff.html"><span class="doc">pair_coeff</span></a> command as in the examples
above, where the first argument is the filename that includes the
exponential-6 parameters for each species. The file includes the
species tag followed by the <em>alpha</em>, <em>epsilon</em> and <em>Rm</em>
parameters. The format of the file is described below.</p>
<p>The second and third arguments specify 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 &#8220;1fluid&#8221;,
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>
<p>The fourth and fifth arguments specify the <em>Rm</em> and <em>epsilon</em> scaling exponents.</p>
<p>The final argument specifies the interaction cutoff.</p>
<hr class="docutils" />
<p>The format of a tabulated file is as follows (without the
parenthesized comments):</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="c1"># exponential-6 parameters for various species (one or more comment or blank lines)</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">h2o</span> <span class="n">exp6</span> <span class="mf">11.00</span> <span class="mf">0.02</span> <span class="mf">3.50</span> <span class="p">(</span><span class="n">species</span><span class="p">,</span> <span class="n">exp6</span><span class="p">,</span> <span class="n">alpha</span><span class="p">,</span> <span class="n">Rm</span><span class="p">,</span> <span class="n">epsilon</span><span class="p">)</span>
<span class="n">no2</span> <span class="n">exp6</span> <span class="mf">13.60</span> <span class="mf">0.01</span> <span class="mf">3.70</span>
<span class="o">...</span>
<span class="n">co2</span> <span class="n">exp6</span> <span class="mf">13.00</span> <span class="mf">0.03</span> <span class="mf">3.20</span>
</pre></div>
</div>
<p>A section begins with a non-blank line whose 1st character is not a
&#8220;#&#8221;; blank lines or lines starting with &#8220;#&#8221; can be used as comments
between sections.</p>
<p>Following a blank line, the next N lines list the species and their
corresponding parameters. The first argument is the species tag, the
second argument is the exp6 tag, the 3rd argument is the <em>alpha</em>
parameter (energy units), the 4th argument is the <em>epsilon</em> parameter
(energy-distance^6 units), and the 5th argument is the <em>Rm</em> parameter
(distance units). If a species tag of &#8220;1fluid&#8221; is listed as a pair
coefficient, a one-fluid approximation is specified where a
concentration-dependent combination of the parameters is computed
through the following equations:</p>
<img alt="_images/pair_exp6_rx_oneFluid.jpg" class="align-center" src="_images/pair_exp6_rx_oneFluid.jpg" />
<p>where</p>
<img alt="_images/pair_exp6_rx_oneFluid2.jpg" class="align-center" src="_images/pair_exp6_rx_oneFluid2.jpg" />
<p>and xa and xb are the mole fractions of a and b, respectively, which
comprise the gas mixture.</p>
<hr class="docutils" />
<p><strong>Mixing, shift, table, tail correction, restart, rRESPA info</strong>:</p>
<p>This pair style does not support mixing. Thus, coefficients for all
I,J pairs must be specified explicitly.</p>
<p>This style does not support the <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> shift option
for the energy of the exp() and 1/r^6 portion of the pair interaction.</p>
<p>This style does not support the pair_modify tail option for adding long-range
tail corrections to energy and pressure for the A,C terms in the
pair interaction.</p>
</div>
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<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>
</div>
<div class="section" id="related-commands">
<h2>Related commands</h2>
<p><a class="reference internal" href="pair_coeff.html"><span class="doc">pair_coeff</span></a></p>
<p><strong>Default:</strong> none</p>
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