pair_style lj/mdf command

pair_style buck/mdf command

pair_style lennard/mdf command

Syntax

pair_style style args
  • style = lj/mdf or buck/mdf or lennard/mdf

  • args = list of arguments for a particular style

    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
    

Examples

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

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

pair_style lennard/mdf 2.5 3.0
pair_coeff * * 1 1
pair_coeff 1 1 1 1.1 2.8 3.0 3.2

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.

_images/pair_mdf-1.jpg

The tapering, f(r), is done by using the Mei, Davenport, Fernando function (Mei).

_images/pair_mdf-2.jpg

where

_images/pair_mdf-3.jpg

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


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

_images/pair_mdf-4.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 or restart files read by the read_data or read_restart commands, or by mixing as described below:

  • epsilon (energy units)
  • sigma (distance units)
  • r_m (distance units)
  • r_cut (distance units)

For the buck/mdf pair_style, the potential energy, E(r), is the standard Buckingham potential:

_images/pair_mdf-5.jpg
  • A (energy units)
  • rho (distance units)
  • C (energy-distance^6 units)
  • r_m (distance units)
  • r_cut$ (distance units)

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

_images/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 or restart files read by the read_data or read_restart commands, or by mixing as described below:

  • A (energy-distance^12 units)
  • B (energy-distance^6 units)
  • r_m (distance units)
  • r_cut (distance units)

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

For atom type pairs I,J and I != J, the epsilon and sigma coefficients and cutoff distance for all of the lj/cut pair styles can be mixed. The default mix value is geometric. See the “pair_modify” command for details.

All of the lj/cut pair styles support the pair_modify shift option for the energy of the Lennard-Jones portion of the pair interaction.

The lj/cut/coul/long and lj/cut/tip4p/long pair styles support the pair_modify table option since they can tabulate the short-range portion of the long-range Coulombic interaction.

All of the lj/cut pair styles support the pair_modify tail option for adding a long-range tail correction to the energy and pressure for the Lennard-Jones portion of the pair interaction.

All of the lj/cut 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.

The lj/cut and lj/cut/coul/long pair styles support the use of the inner, middle, and outer keywords of the run_style respa command, meaning the pairwise forces can be partitioned by distance at different levels of the rRESPA hierarchy. The other styles only support the pair keyword of run_style respa. See the run_style command for details.


Restrictions

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