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### pair_style command

Syntax:

    pair_style style args

- style = one of the styles from the list below
- args = arguments used by a particular style

Examples:

    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

Description:

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 bond_style command to define potentials between pairs of bonded atoms, which typically remain in place for the duration of a simulation.

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.

Hybrid models where specified pairs of atom types interact via different pair potentials can be setup using the hybrid pair style.

The coefficients associated with a pair style are typically set for each pair of atom types, and are specified by the pair_coeff command or read from a file by the read_data or read_restart commands.

The pair_modify 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 restart file is listed on the potential doc page.

In the formulas listed for each pair style, E is the energy of a pairwise interaction between two atoms separated by a distance r. The force between the atoms is the negative derivative of this expression.

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.

Typically, the global cutoff value can be overridden for a specific pair of atom types by the pair_coeff 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 pair_coeff command. The exceptions to this are that pair_style table and hybrid settings cannot be reset. A new pair_style command for these styles will wipe out all previously specified pair_coeff values.

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 pair_coeff command:

- pair_style none - turn off pairwise interactions
- pair_style hybrid - multiple styles of pairwise interactions
- pair_style hybrid/overlay - multiple styles of superposed pairwise interactions

- pair_style airebo - AI-REBO potential
- pair_style born - Born-Mayer-Huggins potential
- pair_style born/coul/long - Born-Mayer-Huggins with long-range Coulomb
- pair_style buck - Buckingham potential
- pair_style buck/coul/cut - Buckingham with cutoff Coulomb
- pair_style buck/coul/long - Buckingham with long-range Coulomb
- pair_style colloid - integrated colloidal potential
- pair_style coul/cut - cutoff Coulombic potential
- pair_style coul/debye - cutoff Coulombic potential with Debye screening
- pair_style coul/long - long-range Coulombic potential
- pair_style dipole/cut - point dipoles with cutoff
- pair_style dpd - dissipative particle dynamics (DPD)
- pair_style dpd/tstat - DPD thermostatting
- pair_style dsmc - Direct Simulation Monte Carlo (DSMC)
- pair_style eam - embedded atom method (EAM)
- pair_style eam/opt - optimized version of EAM
- pair_style eam/alloy - alloy EAM
- pair_style eam/alloy/opt - optimized version of alloy EAM
- pair_style eam/fs - Finnis-Sinclair EAM
- pair_style eam/fs/opt - optimized version of Finnis-Sinclair EAM
- pair_style eim - embedded ion method (EIM)
- pair_style gauss - Gaussian potential
- pair_style gayberne - Gay-Berne ellipsoidal potential
- pair_style gayberne/gpu - GPU-enabled Gay-Berne ellipsoidal potential
- pair_style gran/hertz/history - granular potential with Hertzian interactions
- pair_style gran/hooke - granular potential with history effects
- pair_style gran/hooke/history - granular potential without history effects
- pair_style hbond/dreiding/lj - DREIDING hydrogen bonding LJ potential
- pair_style hbond/dreiding/morse - DREIDING hydrogen bonding Morse potential
- pair_style lj/charmm/coul/charmm - CHARMM potential with cutoff Coulomb
- pair_style lj/charmm/coul/charmm/implicit - CHARMM for implicit solvent
- pair_style lj/charmm/coul/long - CHARMM with long-range Coulomb
- pair_style lj/charmm/coul/long/gpu - GPU-enabled version of CHARMM with long-range Coulomb
- pair_style lj/charmm/coul/long/opt - optimized version of CHARMM with long-range Coulomb
- pair_style lj/class2 - COMPASS (class 2) force field with no Coulomb
- pair_style lj/class2/coul/cut - COMPASS with cutoff Coulomb
- pair_style lj/class2/coul/long - COMPASS with long-range Coulomb
- pair_style lj/cut - cutoff Lennard-Jones potential with no Coulomb
- pair_style lj/cut/gpu - GPU-enabled version of cutoff LJ
- pair_style lj/cut/opt - optimized version of cutoff LJ
- pair_style lj/cut/coul/cut - LJ with cutoff Coulomb
- pair_style lj/cut/coul/cut/gpu - GPU-enabled version of LJ with cutoff Coulomb
- pair_style lj/cut/coul/debye - LJ with Debye screening added to Coulomb
- pair_style lj/cut/coul/long - LJ with long-range Coulomb
- pair_style lj/cut/coul/long/gpu - GPU-enabled version of LJ with long-range Coulomb
- pair_style lj/cut/coul/long/tip4p - LJ with long-range Coulomb for TIP4P water
- pair_style lj/expand - Lennard-Jones for variable size particles
- pair_style lj/expand/gpu - GPU-enabled version of lj/expand
- pair_style lj/gromacs - GROMACS-style Lennard-Jones potential
- pair_style lj/gromacs/coul/gromacs - GROMACS-style LJ and Coulombic potential
- pair_style lj/smooth - smoothed Lennard-Jones potential
- pair_style lj96/cut - Lennard-Jones 9/6 potential
- pair_style lj96/cut/gpu - GPU-enabled version of Lennard-Jones 9/6
- pair_style lubricate - hydrodynamic lubrication forces
- pair_style meam - modified embedded atom method (MEAM)
- pair_style morse - Morse potential
- pair_style morse/gpu - GPU-enabled version of Morse potential
- pair_style morse/opt - optimized version of Morse potential
- pair_style peri/lps - peridynamic LPS potential
- pair_style peri/pmb - peridynamic PMB potential
- pair_style reax - ReaxFF potential
- pair_style resquared - Everaers RE-Squared ellipsoidal potential
- pair_style soft - Soft (cosine) potential
- pair_style sw - Stillinger-Weber 3-body potential
- pair_style table - tabulated pair potential
- pair_style tersoff - Tersoff 3-body potential
- pair_style tersoff/zbl - Tersoff/ZBL 3-body potential
- pair_style yukawa - Yukawa potential
- pair_style yukawa/colloid - screened Yukawa potential for finite-size particles

There are also additional pair styles submitted by users which are included in the LAMMPS distribution. The list of these with links to the individual styles are given in the pair section of this page.

Restrictions:

This command must be used before any coefficients are set by the pair_coeff, read_data, or read_restart commands.

Some pair styles are part of specific packages. They are only enabled if LAMMPS was built with that package. See the Making LAMMPS section for more info on packages. The doc pages for individual pair potentials tell if it is part of a package.

Related commands:

pair_coeff, read_data, pair_modify, kspace_style, dielectric, pair_write

Default:

    pair_style none