lammps/doc/pair_buck.txt

"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)

:line

pair_style buck command :h3
pair_style buck/coul/cut command :h3
pair_style buck/coul/long command :h3

[Syntax:]

pair_style style args :pre

style = {buck} or {buck/coul/cut} or {buck/coul/long}
args = list of arguments for a particular style :ul
  {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) :pre

[Examples:]

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

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 :pre

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 :pre

[Description:]

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

:c,image(Eqs/pair_buck.jpg)

Rc is the cutoff.

The {buck/coul/cut} and {buck/coul/long} styles add a Coulombic term
as described for the "lj/cut"_pair_lj.html pair styles.

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

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

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.

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

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.

:line

[Mixing, shift, table, tail correction, per-atom energy/stress, and
restart 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"_pair_modify.html 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"_pair_modify.html table option since a tabulation
capability has not yet been added to this potential.

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

All of the Buckinham pair styles can calculate per-atom energy and
stress, as used by the "compute epair/atom"_compute_epair_atom.html,
"compute stress/atom"_compute_stress_atom.html, and "dump
custom"_dump.html commands.

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

[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_start.html#2_3 section for
more info.

[Related commands:]

"pair_coeff"_pair_coeff.html

[Default:] none