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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>hybrid/overlay</I>, <I>airebo</I>, <I>buck</I>, <I>buck/coul/cut</I>,
<LI><I>buck/coul/long</I>, <I>coul/cut</I>, <I>coul/long</I>, <I>dipole/cut</I>, <I>dpd</I>, <I>eam</I>,
<LI><I>eam/opt</I>, <I>eam/alloy</I>, <I>eam/alloy/opt</I>, <I>eam/fs</I>, <I>eam/fs/opt</I>,
<LI><I>gayberne</I>, <I>gran/hertzian</I>, <I>gran/history</I>, <I>gran/no_history</I>,
<LI><I>lj/charmm/coul/charmm</I>, <I>lj/charmm/coul/charmm/implicit</I>,
<LI><I>lj/charmm/coul/long</I>, <I>lj/charmm/coul/long/opt</I>, <I>lj/class2</I>,
<LI><I>lj/class2/coul/cut</I>, <I>lj/class2/coul/long</I>, <I>lj/cut</I>, <I>lj/cut/opt</I>,
<LI><I>lj/cut/coul/cut</I>, <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>morse/opt</I>, <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 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 <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.
</P>
<P>The <A HREF = "pair_modify.html">pair_modify</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 HREF = "write_restart.html">restart file</A> or
whether the potential supports calculation of per-atom energy and
stress by the <A HREF = "compute_epair_atom.html">compute epair/atom</A> and
<A HREF = "compute_stress_atom.html">compute stress/atom</A> commands is given on
the potential doc page.
</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> - multiple styles of pairwise interactions
</UL>
<UL><LI><A HREF = "pair_hybrid.html">pair_style hybrid/overlay</A> - multiple styles of superposed pairwise interactions
</UL>
<UL><LI><A HREF = "pair_airebo.html">pair_style airebo</A> - AI-REBO potential
<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_colloid.html">pair_style colloid</A> - integrated colloidal potential
<LI><A HREF = "pair_coul.html">pair_style coul/cut</A> - cutoff Coulombic potential
<LI><A HREF = "pair_coul.html">pair_style coul/long</A> - long-range Coulombic potential
<LI><A HREF = "pair_dpd.html">pair_style dipole/cut</A> - point dipoles with cutoff
<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/opt</A> - optimized version of EAM
<LI><A HREF = "pair_eam.html">pair_style eam/alloy</A> - alloy EAM
<LI><A HREF = "pair_eam.html">pair_style eam/alloy</A> - optimized version of alloy EAM
<LI><A HREF = "pair_eam.html">pair_style eam/fs</A> - Finnis-Sinclair EAM
<LI><A HREF = "pair_eam.html">pair_style eam/fs</A> - optimized version of Finnis-Sinclair EAM
<LI><A HREF = "pair_gayberne.html">pair_style gayberne</A> - Gay-Berne ellipsoidal potential
<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_charmm.html">pair_style lj/charmm/coul/long/opt</A> - optimized version of 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/opt</A> - optimized version of cutoff LJ
<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_morse.html">pair_style morse</A> - optimized version of 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_3">Making
LAMMPS</A> section for more info on packages. The
doc pages for individual pair potentials tell if it is part of a
package.
</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>
</HTML>
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