<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
<p>Set the formula(s) LAMMPS uses to compute pairwise interactions. In
LAMMPS, pair potentials are defined between pairs of atoms that are
within a cutoff distance and the set of active interactions typically
changes over time. See the <a class="reference internal" href="bond_style.html"><em>bond_style</em></a> command to
define potentials between pairs of bonded atoms, which typically
remain in place for the duration of a simulation.</p>
<p>In LAMMPS, pairwise force fields encompass a variety of interactions,
some of which include many-body effects, e.g. EAM, Stillinger-Weber,
Tersoff, REBO potentials. They are still classified as “pairwise”
potentials because the set of interacting atoms changes with time
(unlike molecular bonds) and thus a neighbor list is used to find
nearby interacting atoms.</p>
<p>Hybrid models where specified pairs of atom types interact via
different pair potentials can be setup using the <em>hybrid</em> pair style.</p>
<p>The coefficients associated with a pair style are typically set for
each pair of atom types, and are specified by the
<a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></a> command or read from a file 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.</p>
<p>The <a class="reference internal" href="pair_modify.html"><em>pair_modify</em></a> command sets options for mixing of
type I-J interaction coefficients and adding energy offsets or tail
corrections to Lennard-Jones potentials. Details on these options as
they pertain to individual potentials are described on the doc page
for the potential. Likewise, info on whether the potential
information is stored in a <a class="reference internal" href="write_restart.html"><em>restart file</em></a> is listed
on the potential doc page.</p>
<p>In the formulas listed for each pair style, <em>E</em> is the energy of a
pairwise interaction between two atoms separated by a distance <em>r</em>.
The force between the atoms is the negative derivative of this
expression.</p>
<p>If the pair_style command has a cutoff argument, it sets global
cutoffs for all pairs of atom types. The distance(s) can be smaller
or larger than the dimensions of the simulation box.</p>
<p>Typically, the global cutoff value can be overridden for a specific
pair of atom types by the <a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></a> command. The
pair style settings (including global cutoffs) can be changed by a
subsequent pair_style command using the same style. This will reset
the cutoffs for all atom type pairs, including those previously set
explicitly by a <a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></a> command. The exceptions
to this are that pair_style <em>table</em> and <em>hybrid</em> settings cannot be
reset. A new pair_style command for these styles will wipe out all
previously specified pair_coeff values.</p>
<hr class="docutils" />
<p>Here is an alphabetic list of pair styles defined in LAMMPS. They are
also given in more compact form in the pair section of <a class="reference internal" href="Section_commands.html#cmd-5"><span>this page</span></a>.</p>
<p>Click on the style to display the formula it computes, arguments
specified in the pair_style command, and coefficients specified by the
<li><a class="reference internal" href="pair_born.html"><em>pair_style born/coul/wolf</em></a> - Born-Mayer-Huggins with Coulombics via Wolf potential</li>
<li><a class="reference internal" href="pair_brownian.html"><em>pair_style brownian</em></a> - Brownian potential for Fast Lubrication Dynamics</li>
<li><a class="reference internal" href="pair_brownian.html"><em>pair_style brownian/poly</em></a> - Brownian potential for Fast Lubrication Dynamics with polydispersity</li>
<li><a class="reference internal" href="pair_lubricateU.html"><em>pair_style lubricateU</em></a> - hydrodynamic lubrication forces for Fast Lubrication Dynamics</li>
<li><a class="reference internal" href="pair_lubricateU.html"><em>pair_style lubricateU/poly</em></a> - hydrodynamic lubrication forces for Fast Lubrication with polydispersity</li>
<p>Some pair styles are part of specific packages. They are only 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 on packages.
The doc pages for individual pair potentials tell if it is part of a
package.</p>
</div>
<div class="section" id="related-commands">
<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
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