Syntax:
pair_style style args
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 classed as "pairwise" potential because 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. Mixing, shifting, and tail corrections for the potentials is discussed is the documentation for the pair_modify command.
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:
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.
Related commands:
pair_coeff, read_data, pair_modify, kspace_style, dielectric, pair_write
Default:
pair_style none