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### pair_style buck command

### pair_style buck/coul/cut command

### pair_style buck/coul/long command

Syntax:

    pair_style style args

- style = buck or buck/coul/cut or buck/coul/long
- args = list of arguments for a particular style

      buck args = cutoff
        cutoff = global cutoff for Buckingham interactions (distance units)
      buck/coul/cut args = cutoff (cutoff2)
        cutoff = global cutoff for Buckingham (and Coulombic if only 1 arg) (distance units)
        cutoff2 = global cutoff for Coulombic (optional) (distance units)
      buck/coul/long args = cutoff (cutoff2)
        cutoff = global cutoff for Buckingham (and Coulombic if only 1 arg) (distance units)
        cutoff2 = global cutoff for Coulombic (optional) (distance units)

Examples:

    pair_style buck 2.5
    pair_coeff * * 100.0 1.5 200.0
    pair_coeff * * 100.0 1.5 200.0 3.0

    pair_style buck/coul/cut 10.0
    pair_style buck/coul/cut 10.0 8.0
    pair_coeff * * 100.0 1.5 200.0
    pair_coeff 1 1 100.0 1.5 200.0 9.0
    pair_coeff 1 1 100.0 1.5 200.0 9.0 8.0

    pair_style buck/coul/long 10.0
    pair_style buck/coul/long 10.0 8.0
    pair_coeff * * 100.0 1.5 200.0
    pair_coeff 1 1 100.0 1.5 200.0 9.0

Description:

The buck style computes a Buckingham potential (exp/6 instead of Lennard-Jones 12/6) given by

Rc is the cutoff.

The buck/coul/cut and buck/coul/long styles add a Coulombic term as described for the lj/cut pair styles.

Note that this potential is related to the Born-Mayer-Huggins potential.

The following coefficients must be defined for each pair of atoms types via the pair_coeff command as in the examples above, or in the data file or restart files read by the read_data or read_restart commands:

- A (energy units)
- rho (distance units)
- C (energy-distance^6 units)
- cutoff (distance units)
- cutoff2 (distance units)

The second coefficient, rho, must be greater than zero.

The latter 2 coefficients are optional. If not specified, the global LJ and Coulombic cutoffs are used. If only one cutoff is specified, it is used as the cutoff for both LJ and Coulombic interactions for this type pair. If both coefficients are specified, they are used as the LJ and Coulombic cutoffs for this type pair. You cannot specify 2 cutoffs for style buck, since it has no Coulombic terms.

For buck/coul/long only the LJ cutoff can be specified since a Coulombic cutoff cannot be specified for an individual I,J type pair. All type pairs use the same global Coulombic cutoff specified in the pair_style command.

Mixing, shift, table, tail correction, restart, rRESPA info:

None of the Buckingham pair styles support mixing. Thus, coefficients for all I,J pairs must be specified explicitly.

All of the Buckingham pair styles support the pair_modify shift option for the energy of the exp() and 1/r^6 portion of the pair interaction.

The buck/coul/long pair style does not support the pair_modify table option since a tabulation capability has not yet been added to this potential.

None of the Buckingham pair styles support the pair_modify tail option for adding long-range tail corrections to energy and pressure.

All of the Buckingham pair styles write their information to binary restart files, so pair_style and pair_coeff commands do not need to be specified in an input script that reads a restart file.

All of the Buckingham pair styles can only be used via the pair keyword of the run_style respa command. They do not support the inner, middle, outer keywords.

Restrictions:

The buck/coul/long style is part of the "kspace" package. It is only enabled if LAMMPS was built with that package (which it is by default). See the Making LAMMPS section for more info.

Related commands:

pair_coeff, pair_style born

Default: none