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<title>pair_style coul/cut command — LAMMPS 15 May 2015 version documentation</title>
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<div class="section" id="pair-style-coul-cut-command">
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<span id="index-0"></span><h1>pair_style coul/cut command<a class="headerlink" href="#pair-style-coul-cut-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-cut-gpu-command">
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<h1>pair_style coul/cut/gpu command<a class="headerlink" href="#pair-style-coul-cut-gpu-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-cut-kk-command">
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<h1>pair_style coul/cut/kk command<a class="headerlink" href="#pair-style-coul-cut-kk-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-cut-omp-command">
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<h1>pair_style coul/cut/omp command<a class="headerlink" href="#pair-style-coul-cut-omp-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-debye-command">
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<h1>pair_style coul/debye command<a class="headerlink" href="#pair-style-coul-debye-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-debye-gpu-command">
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<h1>pair_style coul/debye/gpu command<a class="headerlink" href="#pair-style-coul-debye-gpu-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-debye-kk-command">
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<h1>pair_style coul/debye/kk command<a class="headerlink" href="#pair-style-coul-debye-kk-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-debye-omp-command">
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<h1>pair_style coul/debye/omp command<a class="headerlink" href="#pair-style-coul-debye-omp-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-dsf-command">
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<h1>pair_style coul/dsf command<a class="headerlink" href="#pair-style-coul-dsf-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-dsf-gpu-command">
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<h1>pair_style coul/dsf/gpu command<a class="headerlink" href="#pair-style-coul-dsf-gpu-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-dsf-kk-command">
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<h1>pair_style coul/dsf/kk command<a class="headerlink" href="#pair-style-coul-dsf-kk-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-dsf-omp-command">
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<h1>pair_style coul/dsf/omp command<a class="headerlink" href="#pair-style-coul-dsf-omp-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-long-command">
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<h1>pair_style coul/long command<a class="headerlink" href="#pair-style-coul-long-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-long-cs-command">
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<h1>pair_style coul/long/cs command<a class="headerlink" href="#pair-style-coul-long-cs-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-long-omp-command">
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<h1>pair_style coul/long/omp command<a class="headerlink" href="#pair-style-coul-long-omp-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-long-gpu-command">
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<h1>pair_style coul/long/gpu command<a class="headerlink" href="#pair-style-coul-long-gpu-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-long-kk-command">
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<h1>pair_style coul/long/kk command<a class="headerlink" href="#pair-style-coul-long-kk-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-msm-command">
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<h1>pair_style coul/msm command<a class="headerlink" href="#pair-style-coul-msm-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-msm-omp-command">
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<h1>pair_style coul/msm/omp command<a class="headerlink" href="#pair-style-coul-msm-omp-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-streitz-command">
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<h1>pair_style coul/streitz command<a class="headerlink" href="#pair-style-coul-streitz-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-wolf-command">
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<h1>pair_style coul/wolf command<a class="headerlink" href="#pair-style-coul-wolf-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-wolf-kk-command">
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<h1>pair_style coul/wolf/kk command<a class="headerlink" href="#pair-style-coul-wolf-kk-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-coul-wolf-omp-command">
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<h1>pair_style coul/wolf/omp command<a class="headerlink" href="#pair-style-coul-wolf-omp-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-tip4p-cut-command">
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<h1>pair_style tip4p/cut command<a class="headerlink" href="#pair-style-tip4p-cut-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-tip4p-long-command">
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<h1>pair_style tip4p/long command<a class="headerlink" href="#pair-style-tip4p-long-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-tip4p-cut-omp-command">
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<h1>pair_style tip4p/cut/omp command<a class="headerlink" href="#pair-style-tip4p-cut-omp-command" title="Permalink to this headline">¶</a></h1>
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</div>
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<div class="section" id="pair-style-tip4p-long-omp-command">
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<h1>pair_style tip4p/long/omp command<a class="headerlink" href="#pair-style-tip4p-long-omp-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 coul/cut cutoff
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pair_style coul/debye kappa cutoff
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pair_style coul/dsf alpha cutoff
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pair_style coul/long cutoff
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pair_style coul/long/cs cutoff
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pair_style coul/long/gpu cutoff
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pair_style coul/wolf alpha cutoff
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pair_style coul/streitz cutoff keyword alpha
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pair_style tip4p/cut otype htype btype atype qdist cutoff
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pair_style tip4p/long otype htype btype atype qdist cutoff
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</pre></div>
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</div>
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<ul class="simple">
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<li>cutoff = global cutoff for Coulombic interactions</li>
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<li>kappa = Debye length (inverse distance units)</li>
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<li>alpha = damping parameter (inverse 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<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 coul/cut 2.5
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pair_coeff * *
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pair_coeff 2 2 3.5
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</pre></div>
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</div>
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<div class="highlight-python"><div class="highlight"><pre>pair_style coul/debye 1.4 3.0
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pair_coeff * *
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pair_coeff 2 2 3.5
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</pre></div>
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</div>
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<div class="highlight-python"><div class="highlight"><pre>pair_style coul/dsf 0.05 10.0
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pair_coeff * *
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</pre></div>
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</div>
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<div class="highlight-python"><div class="highlight"><pre>pair_style coul/long 10.0
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pair_style coul/long/cs 10.0
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pair_coeff * *
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</pre></div>
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</div>
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<div class="highlight-python"><div class="highlight"><pre>pair_style coul/msm 10.0
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pair_coeff * *
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</pre></div>
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</div>
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<div class="highlight-python"><div class="highlight"><pre>pair_style coul/wolf 0.2 9.0
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pair_coeff * *
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</pre></div>
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</div>
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<div class="highlight-python"><div class="highlight"><pre>pair_style coul/streitz 12.0 ewald
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pair_style coul/streitz 12.0 wolf 0.30
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pair_coeff * * AlO.streitz Al O
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</pre></div>
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</div>
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<div class="highlight-python"><div class="highlight"><pre>pair_style tip4p/cut 1 2 7 8 0.15 12.0
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pair_coeff * *
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</pre></div>
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</div>
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<div class="highlight-python"><div class="highlight"><pre>pair_style tip4p/long 1 2 7 8 0.15 10.0
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pair_coeff * *
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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<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
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<p>The <em>coul/cut</em> style computes the standard Coulombic interaction
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potential given by</p>
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<img alt="_images/pair_coulomb.jpg" class="align-center" src="_images/pair_coulomb.jpg" />
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<p>where C is an energy-conversion constant, Qi and Qj are the charges on
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the 2 atoms, and epsilon is the dielectric constant which can be set
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by the <a class="reference internal" href="dielectric.html"><em>dielectric</em></a> command. The cutoff Rc truncates
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the interaction distance.</p>
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<hr class="docutils" />
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<p>Style <em>coul/debye</em> adds an additional exp() damping factor to the
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Coulombic term, given by</p>
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<img alt="_images/pair_debye.jpg" class="align-center" src="_images/pair_debye.jpg" />
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<p>where kappa is the Debye length. This potential is another way to
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mimic the screening effect of a polar solvent.</p>
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<hr class="docutils" />
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<p>Style <em>coul/dsf</em> computes Coulombic interactions via the damped
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shifted force model described in <a class="reference internal" href="pair_lj.html#fennell"><span>Fennell</span></a>, given by:</p>
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<img alt="_images/pair_coul_dsf.jpg" class="align-center" src="_images/pair_coul_dsf.jpg" />
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<p>where <em>alpha</em> is the damping parameter and erfc() is the
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complementary error-function. The potential corrects issues in the
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Wolf model (described below) to provide consistent forces and energies
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(the Wolf potential is not differentiable at the cutoff) and smooth
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decay to zero.</p>
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<hr class="docutils" />
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<p>Style <em>coul/wolf</em> computes Coulombic interactions via the Wolf
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summation method, described in <a class="reference internal" href="#wolf"><span>Wolf</span></a>, given by:</p>
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<img alt="_images/pair_coul_wolf.jpg" class="align-center" src="_images/pair_coul_wolf.jpg" />
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<p>where <em>alpha</em> is the damping parameter, and erc() and erfc() are
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error-fuction and complementary error-function terms. This potential
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is essentially a short-range, spherically-truncated,
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charge-neutralized, shifted, pairwise <em>1/r</em> summation. With a
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manipulation of adding and substracting a self term (for i = j) to the
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first and second term on the right-hand-side, respectively, and a
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small enough <em>alpha</em> damping parameter, the second term shrinks and
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the potential becomes a rapidly-converging real-space summation. With
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a long enough cutoff and small enough alpha parameter, the energy and
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forces calcluated by the Wolf summation method approach those of the
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Ewald sum. So it is a means of getting effective long-range
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interactions with a short-range potential.</p>
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<hr class="docutils" />
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<p>Style <em>coul/streitz</em> is the Coulomb pair interaction defined as part
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of the Streitz-Mintmire potential, as described in <a class="reference internal" href="#streitz"><span>this paper</span></a>, in which charge distribution about an atom is modeled
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as a Slater 1*s* orbital. More details can be found in the referenced
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paper. To fully reproduce the published Streitz-Mintmire potential,
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which is a variable charge potential, style <em>coul/streitz</em> must be
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used with <a class="reference internal" href="pair_eam.html"><em>pair_style eam/alloy</em></a> (or some other
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short-range potential that has been parameterized appropriately) via
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the <a class="reference internal" href="pair_hybrid.html"><em>pair_style hybrid/overlay</em></a> command. Likewise,
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charge equilibration must be performed via the <a class="reference internal" href="fix_qeq.html"><em>fix qeq/slater</em></a> command. For example:</p>
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<div class="highlight-python"><div class="highlight"><pre>pair_style hybrid/overlay coul/streitz 12.0 wolf 0.31 eam/alloy
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pair_coeff * * coul/streitz AlO.streitz Al O
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pair_coeff * * eam/alloy AlO.eam.alloy Al O
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fix 1 all qeq/slater 1 12.0 1.0e-6 100 coul/streitz
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</pre></div>
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</div>
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<p>The keyword <em>wolf</em> in the coul/streitz command denotes computing
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Coulombic interactions via Wolf summation. An additional damping
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parameter is required for the Wolf summation, as described for the
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coul/wolf potential above. Alternatively, Coulombic interactions can
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be computed via an Ewald summation. For example:</p>
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<div class="highlight-python"><div class="highlight"><pre>pair_style hybrid/overlay coul/streitz 12.0 ewald eam/alloy
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kspace_style ewald 1e-6
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</pre></div>
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</div>
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<p>Keyword <em>ewald</em> does not need a damping parameter, but a
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<a class="reference internal" href="kspace_style.html"><em>kspace_style</em></a> must be defined, which can be style
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<em>ewald</em> or <em>pppm</em>. The Ewald method was used in Streitz and
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Mintmire’s original paper, but a Wolf summation offers a speed-up in
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some cases.</p>
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<p>For the fix qeq/slater command, the <em>qfile</em> can be a filename that
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contains QEq parameters as discussed on the <a class="reference internal" href="fix_qeq.html"><em>fix qeq</em></a>
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command doc page. Alternatively <em>qfile</em> can be replaced by
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“coul/streitz”, in which case the fix will extract QEq parameters from
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the coul/streitz pair style itself.</p>
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<p>See the examples/strietz directory for an example input script that
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uses the Streitz-Mintmire potential. The potentials directory has the
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AlO.eam.alloy and AlO.streitz potential files used by the example.</p>
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<p>Note that the Streiz-Mintmire potential is generally used for oxides,
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but there is no conceptual problem with extending it to nitrides and
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carbides (such as SiC, TiN). Pair coul/strietz used by itself or with
|
|
any other pair style such as EAM, MEAM, Tersoff, or LJ in
|
|
hybrid/overlay mode. To do this, you would need to provide a
|
|
Streitz-Mintmire parameterizaion for the material being modeled.</p>
|
|
<hr class="docutils" />
|
|
<p>Styles <em>coul/long</em> and <em>coul/msm</em> compute the same Coulombic
|
|
interactions as style <em>coul/cut</em> except that an additional damping
|
|
factor is applied so it can be used in conjunction with the
|
|
<a class="reference internal" href="kspace_style.html"><em>kspace_style</em></a> command and its <em>ewald</em> or <em>pppm</em>
|
|
option. The Coulombic cutoff specified for this style means that
|
|
pairwise interactions within this distance are computed directly;
|
|
interactions outside that distance are computed in reciprocal space.</p>
|
|
<p>Style <em>coul/long/cs</em> is identical to <em>coul/long</em> except that a term is
|
|
added for the <a class="reference internal" href="Section_howto.html#howto-25"><span>core/shell model</span></a> to allow
|
|
charges on core and shell particles to be separated by r = 0.0.</p>
|
|
<p>Styles <em>tip4p/cut</em> and <em>tip4p/long</em> implement the coulomb part of
|
|
the TIP4P water model of <a class="reference internal" href="pair_lj.html#jorgensen"><span>(Jorgensen)</span></a>, which introduces
|
|
a massless site located a short distance away from the oxygen atom
|
|
along the bisector of the HOH angle. The atomic types of the oxygen and
|
|
hydrogen atoms, the bond and angle types for OH and HOH interactions,
|
|
and the distance to the massless charge site are specified as
|
|
pair_style arguments. Style <em>tip4p/cut</em> uses a global cutoff for
|
|
Coulomb interactions; style <em>tip4p/long</em> is for use with a long-range
|
|
Coulombic solver (Ewald or PPPM).</p>
|
|
<div class="admonition warning">
|
|
<p class="first admonition-title">Warning</p>
|
|
<p class="last">For each TIP4P water molecule in your system, the atom
|
|
IDs for the O and 2 H atoms must be consecutive, with the O atom
|
|
first. This is to enable LAMMPS to “find” the 2 H atoms associated
|
|
with each O atom. For example, if the atom ID of an O atom in a TIP4P
|
|
water molecule is 500, then its 2 H atoms must have IDs 501 and 502.</p>
|
|
</div>
|
|
<p>See the <a class="reference internal" href="Section_howto.html#howto-8"><span>howto section</span></a> for more
|
|
information on how to use the TIP4P pair styles and lists of
|
|
parameters to set. Note that the neighobr list cutoff for Coulomb
|
|
interactions is effectively extended by a distance 2*qdist when using
|
|
the TIP4P pair style, to account for the offset distance of the
|
|
fictitious charges on O atoms in water molecules. Thus it is
|
|
typically best in an efficiency sense to use a LJ cutoff >= Coulomb
|
|
cutoff + 2*qdist, to shrink the size of the neighbor list. This leads
|
|
to slightly larger cost for the long-range calculation, so you can
|
|
test the trade-off for your model.</p>
|
|
<hr class="docutils" />
|
|
<p>Note that these potentials are designed to be combined with other pair
|
|
potentials via the <a class="reference internal" href="pair_hybrid.html"><em>pair_style hybrid/overlay</em></a>
|
|
command. This is because they have no repulsive core. Hence if they
|
|
are used by themselves, there will be no repulsion to keep two
|
|
oppositely charged particles from moving arbitrarily close to each
|
|
other.</p>
|
|
<p>The following coefficients must be defined for each pair of atoms
|
|
types via the <a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></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"><em>read_data</em></a> or <a class="reference internal" href="read_restart.html"><em>read_restart</em></a>
|
|
commands, or by mixing as described below:</p>
|
|
<ul class="simple">
|
|
<li>cutoff (distance units)</li>
|
|
</ul>
|
|
<p>For <em>coul/cut</em> and <em>coul/debye</em>, the cutoff coefficient is optional.
|
|
If it is not used (as in some of the examples above), the default
|
|
global value specified in the pair_style command is used.</p>
|
|
<p>For <em>coul/long</em> and <em>coul/msm</em> no cutoff can be specified for an
|
|
individual I,J type pair via the pair_coeff command. All type pairs
|
|
use the same global Coulombic cutoff specified in the pair_style
|
|
command.</p>
|
|
<hr class="docutils" />
|
|
<p>Styles with a <em>cuda</em>, <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"><em>Section_accelerate</em></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 USER-CUDA, 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>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>-suffix command-line switch</span></a> when you invoke LAMMPS, or you can
|
|
use the <a class="reference internal" href="suffix.html"><em>suffix</em></a> command in your input script.</p>
|
|
<p>See <a class="reference internal" href="Section_accelerate.html"><em>Section_accelerate</em></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 cutoff distance for the
|
|
<em>coul/cut</em> style can be mixed. The default mix value is <em>geometric</em>.
|
|
See the “pair_modify” command for details.</p>
|
|
<p>The <a class="reference internal" href="pair_modify.html"><em>pair_modify</em></a> shift option is not relevant
|
|
for these pair styles.</p>
|
|
<p>The <em>coul/long</em> style supports the <a class="reference internal" href="pair_modify.html"><em>pair_modify</em></a>
|
|
table option for tabulation of the short-range portion of the
|
|
long-range Coulombic interaction.</p>
|
|
<p>These pair styles do not support the <a class="reference internal" href="pair_modify.html"><em>pair_modify</em></a>
|
|
tail option for adding long-range tail corrections to energy and
|
|
pressure.</p>
|
|
<p>These pair styles write their information to <a class="reference internal" href="restart.html"><em>binary restart files</em></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"><em>run_style respa</em></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<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
|
|
<p>The <em>coul/long</em>, <em>coul/msm</em> and <em>tip4p/long</em> styles are part of the
|
|
KSPACE package. The <em>coul/long/cs</em> style is part of the CORESHELL
|
|
package. They are only enabled if LAMMPS was built with that package
|
|
(which it is by default). See the <a class="reference internal" href="Section_start.html#start-3"><span>Making LAMMPS</span></a> section for more info.</p>
|
|
</div>
|
|
<div class="section" id="related-commands">
|
|
<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
|
|
<p><a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></a>, <a class="reference internal" href="pair_hybrid.html"><em>pair_style, hybrid/overlay</em></a>, <a class="reference internal" href="kspace_style.html"><em>kspace_style</em></a></p>
|
|
<p><strong>Default:</strong> none</p>
|
|
<hr class="docutils" />
|
|
<p id="wolf"><strong>(Wolf)</strong> D. Wolf, P. Keblinski, S. R. Phillpot, J. Eggebrecht, J Chem
|
|
Phys, 110, 8254 (1999).</p>
|
|
<p id="fennell"><strong>(Fennell)</strong> C. J. Fennell, J. D. Gezelter, J Chem Phys, 124,
|
|
234104 (2006).</p>
|
|
<p id="streitz"><strong>(Streitz)</strong> F. H. Streitz, J. W. Mintmire, Phys Rev B, 50, 11996-12003
|
|
(1994).</p>
|
|
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