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<div class="section" id="pair-style-thole-command">
<span id="index-0"></span><h1>pair_style thole command</h1>
</div>
<div class="section" id="pair-style-lj-cut-thole-long-command">
<h1>pair_style lj/cut/thole/long command</h1>
</div>
<div class="section" id="pair-style-lj-cut-thole-long-omp-command">
<h1>pair_style lj/cut/thole/long/omp command</h1>
<div class="section" id="syntax">
<h2>Syntax</h2>
<pre class="literal-block">
pair_style style args
</pre>
<ul class="simple">
<li>style = <em>thole</em> or <em>lj/cut/thole/long</em> or <em>lj/cut/thole/long/omp</em></li>
<li>args = list of arguments for a particular style</li>
</ul>
<pre class="literal-block">
<em>thole</em> args = damp cutoff
damp = global damping parameter
cutoff = global cutoff (distance units)
<em>lj/cut/thole/long</em> or <em>lj/cut/thole/long/omp</em> args = damp cutoff (cutoff2)
damp = global damping parameter
cutoff = global cutoff for LJ (and Thole if only 1 arg) (distance units)
cutoff2 = global cutoff for Thole (optional) (distance units)
</pre>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<pre class="literal-block">
pair_style hybrid/overlay ... thole 2.6 12.0
pair_coeff 1 1 thole 1.0
pair_coeff 1 2 thole 1.0 2.6 10.0
pair_coeff * 2 thole 1.0 2.6
</pre>
<pre class="literal-block">
pair_style lj/cut/thole/long 2.6 12.0
</pre>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>The <em>thole</em> pair styles are meant to be used with force fields that
include explicit polarization through Drude dipoles. This link
describes how to use the <a class="reference internal" href="tutorial_drude.html"><span class="doc">thermalized Drude oscillator model</span></a> in LAMMPS and polarizable models in LAMMPS
are discussed in <a class="reference internal" href="Section_howto.html#howto-25"><span class="std std-ref">this Section</span></a>.</p>
<p>The <em>thole</em> pair style should be used as a sub-style within in the
<a class="reference internal" href="pair_hybrid.html"><span class="doc">pair_hybrid/overlay</span></a> command, in conjunction with a
main pair style including Coulomb interactions, i.e. any pair style
containing <em>coul/cut</em> or <em>coul/long</em> in its style name.</p>
<p>The <em>lj/cut/thole/long</em> pair style is equivalent to, but more convenient that
the frequent combination <em>hybrid/overlay lj/cut/coul/long cutoff thole damp
cutoff2</em>. It is not only a shorthand for this pair_style combination, but
it also allows for mixing pair coefficients instead of listing them all.
The <em>lj/cut/thole/long</em> pair style is also a bit faster because it avoids an
overlay and can benefit from OMP acceleration. Moreover, it uses a more
precise approximation of the direct Coulomb interaction at short range similar
to <a class="reference internal" href="pair_cs.html"><span class="doc">coul/long/cs</span></a>, which stabilizes the temperature of
Drude particles.</p>
<p>The <em>thole</em> pair styles compute the Coulomb interaction damped at
short distances by a function</p>
<div class="math">
\[\begin{equation} T_{ij}(r_{ij}) = 1 - \left( 1 +
\frac{s_{ij} r_{ij} }{2} \right)
\exp \left( - s_{ij} r_{ij} \right) \end{equation}\]</div>
<p>This function results from an adaptation to point charges
<a class="reference internal" href="tutorial_drude.html#noskov"><span class="std std-ref">(Noskov)</span></a> of the dipole screening scheme originally proposed
by <a class="reference internal" href="tutorial_drude.html#thole"><span class="std std-ref">Thole</span></a>. The scaling coefficient <span class="math">\(s_{ij}\)</span> is determined
by the polarizability of the atoms, <span class="math">\(\alpha_i\)</span>, and by a Thole
damping parameter <span class="math">\(a\)</span>. This Thole damping parameter usually takes
a value of 2.6, but in certain force fields the value can depend upon
the atom types. The mixing rule for Thole damping parameters is the
arithmetic average, and for polarizabilities the geometric average
between the atom-specific values.</p>
<div class="math">
\[\begin{equation} s_{ij} = \frac{ a_{ij} }{
(\alpha_{ij})^{1/3} } = \frac{ (a_i + a_j)/2 }{
[(\alpha_i\alpha_j)^{1/2}]^{1/3} } \end{equation}\]</div>
<p>The damping function is only applied to the interactions between the
point charges representing the induced dipoles on polarizable sites,
that is, charges on Drude particles, <span class="math">\(q_{D,i}\)</span>, and opposite
charges, <span class="math">\(-q_{D,i}\)</span>, located on the respective core particles
(to which each Drude particle is bonded). Therefore, Thole screening
is not applied to the full charge of the core particle <span class="math">\(q_i\)</span>, but
only to the <span class="math">\(-q_{D,i}\)</span> part of it.</p>
<p>The interactions between core charges are subject to the weighting
factors set by the <a class="reference internal" href="special_bonds.html"><span class="doc">special_bonds</span></a> command. The
interactions between Drude particles and core charges or
non-polarizable atoms are also subject to these weighting factors. The
Drude particles inherit the 1-2, 1-3 and 1-4 neighbor relations from
their respective cores.</p>
<p>For pair_style <em>thole</em>, 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 example above.</p>
<ul class="simple">
<li>alpha (distance units^3)</li>
<li>damp</li>
<li>cutoff (distance units)</li>
</ul>
<p>The last two coefficients are optional. If not specified the global
Thole damping parameter or global cutoff specified in the pair_style
command are used. In order to specify a cutoff (third argument) a damp
parameter (second argument) must also be specified.</p>
<p>For pair style <em>lj/cut/thole/long</em>, 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.</p>
<ul class="simple">
<li>epsilon (energy units)</li>
<li>sigma (length units)</li>
<li>alpha (distance units^3)</li>
<li>damps</li>
<li>LJ cutoff (distance units)</li>
</ul>
<p>The last two coefficients are optional and default to the global values from
the <em>pair_style</em> command line.</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>
<p><strong>Mixing</strong>:</p>
<p>The <em>thole</em> pair style does not support mixing. Thus, coefficients
for all I,J pairs must be specified explicitly.</p>
<p>The <em>lj/cut/thole/long</em> pair style does support mixing. Mixed coefficients
are defined using</p>
<div class="math">
\[\begin{equation} \alpha_{ij} = \sqrt{\alpha_i\alpha_j}\end{equation}\]</div>
<div class="math">
\[\begin{equation} a_{ij} = \frac 1 2 (a_i + a_j)\end{equation}\]</div>
</div>
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<p>These pair styles are part of the USER-DRUDE package. They are 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 should currently not be used with the <a class="reference internal" href="dihedral_charmm.html"><span class="doc">charmm dihedral style</span></a> if the latter has non-zero 1-4 weighting
factors. This is because the <em>thole</em> pair style does not know which
pairs are 1-4 partners of which dihedrals.</p>
<p>The <em>lj/cut/thole/long</em> pair style should be used with a <a class="reference internal" href="kspace_style.html"><span class="doc">Kspace solver</span></a>
like PPPM or Ewald, which is only enabled if LAMMPS was built with the kspace
package.</p>
</div>
<div class="section" id="related-commands">
<h2>Related commands</h2>
<p><a class="reference internal" href="fix_drude.html"><span class="doc">fix drude</span></a>, <a class="reference internal" href="fix_langevin_drude.html"><span class="doc">fix langevin/drude</span></a>, <a class="reference internal" href="fix_drude_transform.html"><span class="doc">fix drude/transform</span></a>, <a class="reference internal" href="compute_temp_drude.html"><span class="doc">compute temp/drude</span></a>
<a class="reference external" href="pair_lj_cut_coul_long">pair_style lj/cut/coul/long</a></p>
<p><strong>Default:</strong> none</p>
<hr class="docutils" />
<p id="noskov"><strong>(Noskov)</strong> Noskov, Lamoureux and Roux, J Phys Chem B, 109, 6705 (2005).</p>
<p id="thole"><strong>(Thole)</strong> Chem Phys, 59, 341 (1981).</p>
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