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<div class="section" id="pair-style-yukawa-colloid-command">
<span id="index-0"></span><h1>pair_style yukawa/colloid command</h1>
</div>
<div class="section" id="pair-style-yukawa-colloid-gpu-command">
<h1>pair_style yukawa/colloid/gpu command</h1>
</div>
<div class="section" id="pair-style-yukawa-colloid-omp-command">
<h1>pair_style yukawa/colloid/omp command</h1>
<div class="section" id="syntax">
<h2>Syntax</h2>
<pre class="literal-block">
pair_style yukawa/colloid kappa cutoff
</pre>
<ul class="simple">
<li>kappa = screening length (inverse distance units)</li>
<li>cutoff = global cutoff for colloidal Yukawa interactions (distance units)</li>
</ul>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<pre class="literal-block">
pair_style yukawa/colloid 2.0 2.5
pair_coeff 1 1 100.0 2.3
pair_coeff * * 100.0
</pre>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>Style <em>yukawa/colloid</em> computes pairwise interactions with the formula</p>
<img alt="_images/pair_yukawa_colloid.jpg" class="align-center" src="_images/pair_yukawa_colloid.jpg" />
<p>where Ri and Rj are the radii of the two particles and Rc is the
cutoff.</p>
<p>In contrast to <a class="reference internal" href="pair_yukawa.html"><span class="doc">pair_style yukawa</span></a>, this functional
form arises from the Coulombic interaction between two colloid
particles, screened due to the presence of an electrolyte, see the
book by <a class="reference internal" href="#safran"><span class="std std-ref">Safran</span></a> for a derivation in the context of DVLO
theory. <a class="reference internal" href="pair_yukawa.html"><span class="doc">Pair_style yukawa</span></a> is a screened Coulombic
potential between two point-charges and uses no such approximation.</p>
<p>This potential applies to nearby particle pairs for which the Derjagin
approximation holds, meaning h &lt;&lt; Ri + Rj, where h is the
surface-to-surface separation of the two particles.</p>
<p>When used in combination with <a class="reference internal" href="pair_colloid.html"><span class="doc">pair_style colloid</span></a>,
the two terms become the so-called DLVO potential, which combines
electrostatic repulsion and van der Waals attraction.</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, or in the data file or restart files read by the
<a class="reference internal" href="read_data.html"><span class="doc">read_data</span></a> or <a class="reference internal" href="read_restart.html"><span class="doc">read_restart</span></a>
commands, or by mixing as described below:</p>
<ul class="simple">
<li>A (energy/distance units)</li>
<li>cutoff (distance units)</li>
</ul>
<p>The prefactor A is determined from the relationship between surface
charge and surface potential due to the presence of electrolyte. Note
that the A for this potential style has different units than the A
used in <a class="reference internal" href="pair_yukawa.html"><span class="doc">pair_style yukawa</span></a>. For low surface
potentials, i.e. less than about 25 mV, A can be written as:</p>
<pre class="literal-block">
A = 2 * PI * R*eps*eps0 * kappa * psi^2
</pre>
<p>where</p>
<ul class="simple">
<li>R = colloid radius (distance units)</li>
<li>eps0 = permittivity of free space (charge^2/energy/distance units)</li>
<li>eps = relative permittivity of fluid medium (dimensionless)</li>
<li>kappa = inverse screening length (1/distance units)</li>
<li>psi = surface potential (energy/charge units)</li>
</ul>
<p>The last coefficient is optional. If not specified, the global
yukawa/colloid cutoff is used.</p>
<hr class="docutils" />
<p>Styles with a <em>gpu</em>, <em>intel</em>, <em>kk</em>, <em>omp</em>, or <em>opt</em> suffix are
functionally the same as the corresponding style without the suffix.
They have been optimized to run faster, depending on your available
hardware, as discussed in <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></a>
of the manual. The accelerated styles take the same arguments and
should produce the same results, except for round-off and precision
issues.</p>
<p>These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
USER-OMP and OPT packages, respectively. They are only enabled if
LAMMPS was built with those packages. 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>
<p>You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the <a class="reference internal" href="Section_start.html#start-7"><span class="std std-ref">-suffix command-line switch</span></a> when you invoke LAMMPS, or you can
use the <a class="reference internal" href="suffix.html"><span class="doc">suffix</span></a> command in your input script.</p>
<p>See <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></a> of the manual for
more instructions on how to use the accelerated styles effectively.</p>
<hr class="docutils" />
<p><strong>Mixing, shift, table, tail correction, restart, rRESPA info</strong>:</p>
<p>For atom type pairs I,J and I != J, the A coefficient and cutoff
distance for this pair style can be mixed. A is an energy value mixed
like a LJ epsilon. The default mix value is <em>geometric</em>. See the
&#8220;pair_modify&#8221; command for details.</p>
<p>This pair style supports the <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> shift
option for the energy of the pair interaction.</p>
<p>The <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> table option is not relevant
for this pair style.</p>
<p>This pair style does not support the <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a>
tail option for adding long-range tail corrections to energy and
pressure.</p>
<p>This pair style writes its information to <a class="reference internal" href="restart.html"><span class="doc">binary restart files</span></a>, so pair_style and pair_coeff commands do not need
to be specified in an input script that reads a restart file.</p>
<p>This pair style can only be used via the <em>pair</em> keyword of the
<a class="reference internal" href="run_style.html"><span class="doc">run_style respa</span></a> command. It does not support the
<em>inner</em>, <em>middle</em>, <em>outer</em> keywords.</p>
</div>
<hr class="docutils" />
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<p>This style is part of the COLLOID 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>
<p>This pair style requires that atoms be finite-size spheres with a
diameter, as defined by the <a class="reference internal" href="atom_style.html"><span class="doc">atom_style sphere</span></a>
command.</p>
<p>Per-particle polydispersity is not yet supported by this pair style;
per-type polydispersity is allowed. This means all particles of the
same type must have the same diameter. Each type can have a different
diameter.</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>
<hr class="docutils" />
<p id="safran"><strong>(Safran)</strong> Safran, Statistical Thermodynamics of Surfaces, Interfaces,
And Membranes, Westview Press, ISBN: 978-0813340791 (2003).</p>
</div>
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