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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 class="toctree-l1"><a class="reference internal" href="Section_start.html">2. Getting Started</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_commands.html">3. Commands</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_packages.html">4. Packages</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_accelerate.html">5. Accelerating LAMMPS performance</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_howto.html">6. How-to discussions</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_example.html">7. Example problems</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_perf.html">8. Performance & scalability</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_tools.html">9. Additional tools</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_modify.html">10. Modifying & extending LAMMPS</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_python.html">11. Python interface to LAMMPS</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_errors.html">12. Errors</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_history.html">13. Future and history</a></li>
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<li>pair_style body command</li>
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<div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article">
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<div class="section" id="pair-style-body-command">
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<span id="index-0"></span><h1>pair_style body 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">body</span> <span class="n">cutoff</span>
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</pre></div>
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</div>
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<p>cutoff = global cutoff for interactions (distance units)</p>
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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">body</span> <span class="mf">3.0</span>
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<span class="n">pair_coeff</span> <span class="o">*</span> <span class="o">*</span> <span class="mf">1.0</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">1</span> <span class="mf">1.0</span> <span class="mf">1.5</span> <span class="mf">2.5</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>body</em> is for use with body particles and calculates pairwise
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body/body interactions as well as interactions between body and
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point-particles. See <a class="reference internal" href="Section_howto.html#howto-14"><span class="std std-ref">Section_howto 14</span></a>
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of the manual and the <a class="reference internal" href="body.html"><span class="doc">body</span></a> doc page for more details on
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using body particles.</p>
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<p>This pair style is designed for use with the “nparticle” body style,
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which is specified as an argument to the “atom-style body” command.
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See the <a class="reference internal" href="body.html"><span class="doc">body</span></a> doc page for more details about the body
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styles LAMMPS supports. The “nparticle” style treats a body particle
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as a rigid body composed of N sub-particles.</p>
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<p>The coordinates of a body particle are its center-of-mass (COM). If
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the COMs of a pair of body particles are within the cutoff (global or
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type-specific, as specified above), then all interactions between
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pairs of sub-particles in the two body particles are computed.
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E.g. if the first body particle has 3 sub-particles, and the second
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has 10, then 30 interactions are computed and summed to yield the
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total force and torque on each body particle.</p>
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<div class="admonition note">
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<p class="first admonition-title">Note</p>
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<p class="last">In the example just described, all 30 interactions are computed
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even if the distance between a particular pair of sub-particles is
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greater than the cutoff. Likewise, no interaction between two body
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particles is computed if the two COMs are further apart than the
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cutoff, even if the distance between some pairs of their sub-particles
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is within the cutoff. Thus care should be used in defining the cutoff
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distances for body particles, depending on their shape and size.</p>
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</div>
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<p>Similar rules apply for a body particle interacting with a point
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particle. The distance between the two particles is calculated using
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the COM of the body particle and the position of the point particle.
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If the distance is within the cutoff and the body particle has N
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sub-particles, then N interactions with the point particle are
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computed and summed. If the distance is not within the cutoff, no
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interactions between the body and point particle are computed.</p>
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<p>The interaction between two sub-particles, or a sub-particle and point
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particle, or betwee two point particles is computed as a Lennard-Jones
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interaction, using the standard formula</p>
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<img alt="_images/pair_lj.jpg" class="align-center" src="_images/pair_lj.jpg" />
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<p>where Rc is the cutoff. As explained above, an interaction involving
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one or two body sub-particles may be computed even for r > Rc.</p>
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<p>For style <em>body</em>, the following coefficients must be defined for each
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pair of atoms types via the <a class="reference internal" href="pair_coeff.html"><span class="doc">pair_coeff</span></a> command as in
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the examples 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:</p>
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<ul class="simple">
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<li>epsilon (energy units)</li>
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<li>sigma (distance units)</li>
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<li>cutoff (distance units)</li>
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</ul>
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<p>The last coefficient is optional. If not specified, the global cutoff
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is used.</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 epsilon and sigma coefficients
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and cutoff distance for all of this pair style can be mixed. The
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default mix value is <em>geometric</em>. See the “pair_modify” command for
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details.</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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shift, table, and tail options.</p>
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<p>This pair style does not write its information to <a class="reference internal" href="restart.html"><span class="doc">binary restart files</span></a>.</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 BODY package. It is only enabled if LAMMPS
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was built with that package. See the <a class="reference internal" href="Section_start.html#start-2-3"><span class="std std-ref">Making LAMMPS</span></a> section for more info.</p>
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<p>Defining particles to be bodies so they participate in body/body or
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body/particle interactions requires the use of the <a class="reference internal" href="atom_style.html"><span class="doc">atom_style body</span></a> command.</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>, <a class="reference internal" href="fix_rigid.html"><span class="doc">fix rigid</span></a></p>
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<p><strong>Default:</strong> none</p>
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