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)

where rho is an ionic-pair dependent length parameter, and 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.  For
{buck/coul/long}, an additional damping factor is applied to the
Coulombic term so it can be used in conjunction with the
"kspace_style"_kspace_style.html command and its {ewald} or {pppm}
option.  The Coulombic cutoff specified for this style means that
pairwise interactions within this distance are computed directly;
interactions outside that distance are computed in reciprocal space.

If one cutoff is specified for the {born/coul/cut} and
{born/coulk/long} styles, it is used for both the A,C and Coulombic
terms.  If two cutoffs are specified, the first is used as the cutoff
for the A,C terms, and the second is the cutoff for the Coulombic
term.

Note that these potentials are related to the "Born-Mayer-Huggins
potential"_pair_born.html.

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 second coefficient, rho, must be greater than zero.

The latter 2 coefficients are optional.  If not specified, the global
A,C and Coulombic cutoffs are used.  If only one cutoff is specified,
it is used as the cutoff for both A,C and Coulombic interactions for
this type pair.  If both coefficients are specified, they are used as
the A,C 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.

:line

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

These pair styles do not support mixing.  Thus, coefficients for all
I,J pairs must be specified explicitly.

These 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.

These styles support the pair_modify tail option for adding long-range
tail corrections to energy and pressure for the A,C terms in the
pair interaction.

These 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.

These styles can only be used via the {pair} keyword of the "run_style
respa"_run_style.html 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_start.html#2_3 section for
more info.

[Related commands:]

"pair_coeff"_pair_coeff.html, "pair_style born"_pair_born.html

[Default:] none