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