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<title>pair_style yukawa/colloid command — LAMMPS documentation</title>
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<li class="toctree-l1"><a class="reference internal" href="Section_intro.html">1. Introduction</a></li>
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<li>pair_style yukawa/colloid command</li>
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<div class="section" id="pair-style-yukawa-colloid-command">
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<span id="index-0"></span><h1>pair_style yukawa/colloid command</h1>
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</div>
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<div class="section" id="pair-style-yukawa-colloid-gpu-command">
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<h1>pair_style yukawa/colloid/gpu command</h1>
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</div>
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<div class="section" id="pair-style-yukawa-colloid-omp-command">
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<h1>pair_style yukawa/colloid/omp command</h1>
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<div class="section" id="syntax">
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<h2>Syntax</h2>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">yukawa</span><span class="o">/</span><span class="n">colloid</span> <span class="n">kappa</span> <span class="n">cutoff</span>
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</pre></div>
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</div>
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<ul class="simple">
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<li>kappa = screening length (inverse distance units)</li>
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<li>cutoff = global cutoff for colloidal Yukawa interactions (distance units)</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</h2>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">yukawa</span><span class="o">/</span><span class="n">colloid</span> <span class="mf">2.0</span> <span class="mf">2.5</span>
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<span class="n">pair_coeff</span> <span class="mi">1</span> <span class="mi">1</span> <span class="mf">100.0</span> <span class="mf">2.3</span>
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<span class="n">pair_coeff</span> <span class="o">*</span> <span class="o">*</span> <span class="mf">100.0</span>
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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</h2>
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<p>Style <em>yukawa/colloid</em> computes pairwise interactions with the formula</p>
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<img alt="_images/pair_yukawa_colloid.jpg" class="align-center" src="_images/pair_yukawa_colloid.jpg" />
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<p>where Ri and Rj are the radii of the two particles and Rc is the
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cutoff.</p>
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<p>In contrast to <a class="reference internal" href="pair_yukawa.html"><span class="doc">pair_style yukawa</span></a>, this functional
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form arises from the Coulombic interaction between two colloid
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particles, screened due to the presence of an electrolyte, see the
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book by <a class="reference internal" href="#safran"><span class="std std-ref">Safran</span></a> for a derivation in the context of DVLO
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theory. <a class="reference internal" href="pair_yukawa.html"><span class="doc">Pair_style yukawa</span></a> is a screened Coulombic
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potential between two point-charges and uses no such approximation.</p>
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<p>This potential applies to nearby particle pairs for which the Derjagin
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approximation holds, meaning h << Ri + Rj, where h is the
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surface-to-surface separation of the two particles.</p>
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<p>When used in combination with <a class="reference internal" href="pair_colloid.html"><span class="doc">pair_style colloid</span></a>,
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the two terms become the so-called DLVO potential, which combines
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electrostatic repulsion and van der Waals attraction.</p>
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<p>The following coefficients must be defined for each pair of atoms
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types via the <a class="reference internal" href="pair_coeff.html"><span class="doc">pair_coeff</span></a> command as in the examples
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above, or in the data file or restart files read by the
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<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>
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commands, or by mixing as described below:</p>
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<ul class="simple">
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<li>A (energy/distance units)</li>
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<li>cutoff (distance units)</li>
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</ul>
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<p>The prefactor A is determined from the relationship between surface
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charge and surface potential due to the presence of electrolyte. Note
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that the A for this potential style has different units than the A
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used in <a class="reference internal" href="pair_yukawa.html"><span class="doc">pair_style yukawa</span></a>. For low surface
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potentials, i.e. less than about 25 mV, A can be written as:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">A</span> <span class="o">=</span> <span class="mi">2</span> <span class="o">*</span> <span class="n">PI</span> <span class="o">*</span> <span class="n">R</span><span class="o">*</span><span class="n">eps</span><span class="o">*</span><span class="n">eps0</span> <span class="o">*</span> <span class="n">kappa</span> <span class="o">*</span> <span class="n">psi</span><span class="o">^</span><span class="mi">2</span>
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</pre></div>
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</div>
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<p>where</p>
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<ul class="simple">
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<li>R = colloid radius (distance units)</li>
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<li>eps0 = permittivity of free space (charge^2/energy/distance units)</li>
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<li>eps = relative permittivity of fluid medium (dimensionless)</li>
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<li>kappa = inverse screening length (1/distance units)</li>
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<li>psi = surface potential (energy/charge units)</li>
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</ul>
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<p>The last coefficient is optional. If not specified, the global
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yukawa/colloid cutoff is used.</p>
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<hr class="docutils" />
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<p>Styles with a <em>gpu</em>, <em>intel</em>, <em>kk</em>, <em>omp</em>, or <em>opt</em> suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed in <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></a>
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.</p>
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<p>These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
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USER-OMP and OPT packages, respectively. They are only enabled if
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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>
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<p>You can specify the accelerated styles explicitly in your input script
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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
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use the <a class="reference internal" href="suffix.html"><span class="doc">suffix</span></a> command in your input script.</p>
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<p>See <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></a> of the manual for
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more instructions on how to use the accelerated styles effectively.</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, the A coefficient and cutoff
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distance for this pair style can be mixed. A is an energy value mixed
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like a LJ epsilon. The default mix value is <em>geometric</em>. See the
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“pair_modify” command for details.</p>
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<p>This pair style supports the <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> shift
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option for the energy of the pair interaction.</p>
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<p>The <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a> table option is not relevant
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for this pair style.</p>
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<p>This pair style does not support the <a class="reference internal" href="pair_modify.html"><span class="doc">pair_modify</span></a>
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tail option for adding long-range tail corrections to energy and
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pressure.</p>
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<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
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to be specified in an input script that reads a restart file.</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"><span class="doc">run_style respa</span></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</h2>
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<p>This style is part of the COLLOID package. It is only enabled if
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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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<p>This pair style requires that atoms be finite-size spheres with a
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diameter, as defined by the <a class="reference internal" href="atom_style.html"><span class="doc">atom_style sphere</span></a>
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command.</p>
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<p>Per-particle polydispersity is not yet supported by this pair style;
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per-type polydispersity is allowed. This means all particles of the
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same type must have the same diameter. Each type can have a different
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diameter.</p>
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</div>
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<div class="section" id="related-commands">
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<h2>Related commands</h2>
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<p><a class="reference internal" href="pair_coeff.html"><span class="doc">pair_coeff</span></a></p>
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<p><strong>Default:</strong> none</p>
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<hr class="docutils" />
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<p id="safran"><strong>(Safran)</strong> Safran, Statistical Thermodynamics of Surfaces, Interfaces,
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And Membranes, Westview Press, ISBN: 978-0813340791 (2003).</p>
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