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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
</CENTER>
<HR>
<H3>pair_style command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>pair_style style args
</PRE>
<UL><LI>style = one of the following
<UL><LI><I>none</I>, <I>hybrid</I>, <I>buck</I>, <I>buck/coul/cut</I>, <I>buck/coul/long</I>, <I>dpd</I>,
<LI><I>eam</I>, <I>eam/alloy</I> or <I>eam/fs</I>, <I>gran/hertzian</I>, <I>gran/history</I>,
<LI><I>gran/no_history</I>, <I>lj/charmm/coul/charmm</I>,
<LI><I>lj/charmm/coul/charmm/implicit</I> or <I>lj/charmm/coul/long</I>,
<LI><I>lj/class2</I>, <I>lj/class2/coul/cut</I> or <I>lj/class2/coul/long</I>, <I>lj/cut</I>,
<LI><I>lj/cut/coul/cut</I> or <I>lj/cut/coul/debye</I>, <I>lj/cut/coul/long</I>,
<LI><I>lj/cut/coul/long/tip4p</I>, <I>lj/expand</I>, <I>lj/smooth</I>, <I>meam</I>, <I>morse</I>,
<LI><I>soft</I>, <I>sw</I>, <I>table</I>, <I>tersoff</I>, <I>yukawa</I>
</UL>
<LI>args = arguments used by a particular style
</UL>
<P><B>Examples:</B>
</P>
<PRE>pair_style lj/cut 2.5
pair_style eam/alloy
pair_style hybrid lj/charmm/coul/long 10.0 eam
pair_style table linear 1000
pair_style none
</PRE>
<P><B>Description:</B>
</P>
<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 HREF = "bond_style.html">bond_style</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 classed as "pairwise"
potential because the set of interacting atoms changes with time
(unlike a bonded system) 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 <I>hybrid</I> 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 HREF = "pair_coeff.html">pair_coeff</A> command or read from a file by the
<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
commands. Mixing, shifting, and tail corrections for the potentials
is discussed is the documentation for the
<A HREF = "pair_modify.html">pair_modify</A> command.
</P>
<P>In the formulas listed for each pair style, <I>E</I> is the energy of a
pairwise interaction between two atoms separated by a distance <I>r</I>.
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 HREF = "pair_coeff.html">pair_coeff</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 HREF = "pair_coeff.html">pair_coeff</A> command. The exceptions
to this are that pair_style <I>table</I> and <I>hybrid</I> settings cannot be
reset. A new pair_style command for these styles will wipe out all
previously specified pair_coeff values.
</P>
<HR>
<P>Here is an alphabetic list of pair styles defined in LAMMPS. Click on
the style to display the formula it computes, arguments specified in
the pair_style command, and coefficients specified by the associated
<A HREF = "pair_coeff.html">pair_coeff</A> command:
</P>
<UL><LI><A HREF = "pair_none.html">pair_style none</A> - turn off pairwise interactions
<LI><A HREF = "pair_hybrid.html">pair_style hybrid</A> - define multiple styles of pairwise interactions
</UL>
<UL><LI><A HREF = "pair_buck.html">pair_style buck</A> - Buckingham potential
<LI><A HREF = "pair_buck.html">pair_style buck/coul/cut</A> - Buckinhham with cutoff Coulomb
<LI><A HREF = "pair_buck.html">pair_style buck/coul/long</A> - Buckingham with long-range Coulomb
<LI><A HREF = "pair_dpd.html">pair_style dpd</A> - dissipative particle dynamics (DPD)
<LI><A HREF = "pair_eam.html">pair_style eam</A> - embedded atom method (EAM)
<LI><A HREF = "pair_eam.html">pair_style eam/alloy</A> - alloy EAM
<LI><A HREF = "pair_eam.html">pair_style eam/fs</A> - Finnis-Sinclair EAM
<LI><A HREF = "pair_gran.html">pair_style gran/hertzian</A> - granular potential with Hertizain interactions
<LI><A HREF = "pair_gran.html">pair_style gran/history</A> - granular potential with history effects
<LI><A HREF = "pair_gran.html">pair_style gran/no_history</A> - granular potential without history effects
<LI><A HREF = "pair_charmm.html">pair_style lj/charmm/coul/charmm</A> - CHARMM potential with cutoff Coulomb
<LI><A HREF = "pair_charmm.html">pair_style lj/charmm/coul/charmm/implicit</A> - CHARMM for implicit solvent
<LI><A HREF = "pair_charmm.html">pair_style lj/charmm/coul/long</A> - CHARMM with long-range Coulomb
<LI><A HREF = "pair_class2.html">pair_style lj/class2</A> - COMPASS (class 2) force field with no Coulomb
<LI><A HREF = "pair_class2.html">pair_style lj/class2/coul/cut</A> - COMPASS with cutoff Coulomb
<LI><A HREF = "pair_class2.html">pair_style lj/class2/coul/long</A> - COMPASS with long-range Coulomb
<LI><A HREF = "pair_lj.html">pair_style lj/cut</A> - cutoff Lennard-Jones potential with no Coulomb
<LI><A HREF = "pair_lj.html">pair_style lj/cut/coul/cut</A> - LJ with cutoff Coulomb
<LI><A HREF = "pair_lj.html">pair_style lj/cut/coul/debye</A> - LJ with Debye damping added to Coulomb
<LI><A HREF = "pair_lj.html">pair_style lj/cut/coul/long</A> - LJ with long-range Coulomb
<LI><A HREF = "pair_lj.html">pair_style lj/cut/coul/long/tip4p</A> - LJ with long-range Coulomb for TIP4P water
<LI><A HREF = "pair_lj_expand.html">pair_style lj/expand</A> - Lennard-Jones for variable size particles
<LI><A HREF = "pair_lj_smooth.html">pair_style lj/smooth</A> - smoothed Lennard-Jones potential
<LI><A HREF = "pair_meam.html">pair_style meam</A> - modified embedded atom method (MEAM)
<LI><A HREF = "pair_morse.html">pair_style morse</A> - Morse potential
<LI><A HREF = "pair_soft.html">pair_style soft</A> - Soft (cosine) potential
<LI><A HREF = "pair_sw.html">pair_style sw</A> - Stillinger-Weber 3-body potential
<LI><A HREF = "pair_table.html">pair_style table</A> - tabulated pair potential
<LI><A HREF = "pair_tersoff.html">pair_style tersoff</A> - Tersoff 3-body potential
<LI><A HREF = "pair_yukawa.html">pair_style yukawa</A> - Yukawa potential
</UL>
<HR>
<P><B>Restrictions:</B>
</P>
<P>This command must be used before any coefficients are set by the
<A HREF = "pair_coeff.html">pair_coeff</A>, <A HREF = "read_data.html">read_data</A>, or
<A HREF = "read_restart.html">read_restart</A> commands.
</P>
<P>Some pair styles are part of specific packages. They are only enabled
if LAMMPS was built with that package. See the <A HREF = "Section_start.html#2_2">Making
LAMMPS</A> section for more info.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "pair_coeff.html">pair_coeff</A>, <A HREF = "read_data.html">read_data</A>,
<A HREF = "pair_modify.html">pair_modify</A>, <A HREF = "kspace_style.html">kspace_style</A>,
<A HREF = "dielectric.html">dielectric</A>, <A HREF = "pair_write.html">pair_write</A>
</P>
<P><B>Default:</B>
</P>
<PRE>pair_style none
</PRE>
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