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

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

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pair_style lj/mdf command :h3
pair_style buck/mdf command :h3
pair_style lennard/mdf command :h3

[Syntax:]

pair_style style args :pre

style = {lj/mdf} or {buck/mdf} or {lennard/mdf} :ulb,l
args = list of arguments for a particular style :l
  {lj/mdf} args = cutoff1 cutoff2
    cutoff1 = inner cutoff for the start of the tapering function
    cutoff1 = out cutoff for the end of the tapering function
  {buck/mdf} args = cutoff1 cutoff2
    cutoff1 = inner cutoff for the start of the tapering function
    cutoff1 = out cutoff for the end of the tapering function
  {lennard/mdf} args = cutoff1 cutoff2
    cutoff1 = inner cutoff for the start of the tapering function
    cutoff1 = out cutoff for the end of the tapering function :pre
:ule

[Examples:]

pair_style lj/mdf 2.5 3.0
pair_coeff * * 1.0 1.0
pair_coeff 1 1 1.1 2.8 3.0 3.2 :pre

pair_style buck 2.5 3.0
pair_coeff * * 100.0 1.5 200.0
pair_coeff * * 100.0 1.5 200.0 3.0 3.5 :pre

pair_style lennard/mdf 2.5 3.0
pair_coeff * * 1.0 1.0
pair_coeff 1 1 1021760.3664 2120.317338 3.0 3.2 :pre

[Description:]

The {lj/mdf}, {buck/mdf} and {lennard/mdf} compute the standard 12-6
Lennard-Jones and Buckingham potential with the addition of a taper
function that ramps the energy and force smoothly to zero between an
inner and outer cutoff.

:c,image(Eqs/pair_mdf-1.jpg)

The tapering, {f(r)}, is done by using the Mei, Davenport, Fernando
function "(Mei)"_#Mei.

:c,image(Eqs/pair_mdf-2.jpg)

where

:c,image(Eqs/pair_mdf-3.jpg)

Here {r_m} is the inner cutoff radius and {r_cut} is the outer cutoff
radius.

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For the {lj/mdf} pair_style, the potential energy, {E(r)}, is the
standard 12-6 Lennard-Jones written in the epsilon/sigma form:

:c,image(Eqs/pair_mdf-4.jpg)

Either the first two or all of 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 read by the
"read_data"_read_data.html. The two cutoffs default to the global
values and epsilon and sigma can also be determined by mixing as
described below:

epsilon (energy units)
sigma (distance units)
r_m (distance units)
r_{cut} (distance units) :ul

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For the {buck/mdf} pair_style, the potential energy, {E(r)}, is the
standard Buckingham potential with three required coefficients.
The two cutoffs can be omitted and default to the corresponding
global values:

:c,image(Eqs/pair_mdf-5.jpg)

A (energy units)
\rho (distance units)
C (energy-distance^6 units)
r_m (distance units)
r_{cut} (distance units) :ul

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For the {lennard/mdf} pair_style, the potential energy, {E(r)}, is the
standard 12-6 Lennard-Jones written in the A/B form:

:c,image(Eqs/pair_mdf-6.jpg)

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 read by the read_data commands, or by mixing as described below.
The two cutoffs default to their global values and must be either both
given or both left out:

A (energy-distance^12 units)
B (energy-distance^6 units)
r_m (distance units)
r_{cut} (distance units) :ul

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

For atom type pairs I,J and I != J, the epsilon and sigma coefficients
and cutoff distances for the lj/mdf pair style can be mixed.
The default mix value is {geometric}.  See the "pair_modify" command
for details. The other two pair styles buck/mdf and lennard/mdf do not
support mixing, so all I,J pairs of coefficients must be specified
explicitly.

None of the lj/mdf, buck/mdf, or lennard/mdf pair styles supports
the "pair_modify"_pair_modify.html shift option or long-range
tail corrections to pressure and energy.

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.

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[Restrictions:]

These pair styles can only be used if LAMMPS was built with the
USER-MISC package.  See the "Build package"_Build_package.html doc
page for more info.

[Related commands:]

"pair_coeff"_pair_coeff.html

[Default:] none

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:link(Mei)
[(Mei)] Mei, Davenport, Fernando, Phys Rev B, 43 4653 (1991)
