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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<a class="headerlink" href="#pair-style-thole-command" title="Permalink to this headline">¶</a></h1>
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<div class="section" id="syntax">
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<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>pair_style thole damp cutoff
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</pre></div>
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</div>
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<ul class="simple">
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<li>thole = style name</li>
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<li>damp = global damping parameter</li>
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<li>cutoff = global cutoff</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<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>pair_style hybrid/overlay ... thole 2.6 12.0
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pair_coeff 1 1 thole 1.0
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pair_coeff 1 2 thole 1.0 2.6 10.0
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pair_coeff * 2 thole 1.0 2.6
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</pre></div>
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</div>
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<div class="section" id="description">
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<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
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<p>The <em>thole</em> pair style is 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"><em>thermalized Drude oscillator model</em></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>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"><em>pair_hybrid/overlay</em></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>thole</em> pair style computes 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>(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>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"><em>special_bonds</em></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>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"><em>pair_coeff</em></a> command as in the example
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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><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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</div>
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<div class="section" id="restrictions">
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<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></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>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"><em>charmm dihedral style</em></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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</div>
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<div class="section" id="related-commands">
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<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
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<p><a class="reference internal" href="fix_drude.html"><em>fix drude</em></a>, <a class="reference internal" href="fix_langevin_drude.html"><em>fix langevin/drude</em></a>, <a class="reference internal" href="fix_drude_transform.html"><em>fix drude/transform</em></a>, <a class="reference internal" href="compute_temp_drude.html"><em>compute temp/drude</em></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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