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.
![Eqs/pair_mdf-1.jpg](Eqs/pair_mdf-1.jpg)
The tapering, f(r), is done by using the Mei, Davenport, Fernando function (Mei).
![Eqs/pair_mdf-2.jpg](Eqs/pair_mdf-2.jpg)
where
![Eqs/pair_mdf-3.jpg](Eqs/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:
![Eqs/pair_mdf-4.jpg](Eqs/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 12-6 Lennard-Jones written in the epsilon/sigma form:
![Eqs/pair_mdf-5.jpg](Eqs/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:
![Eqs/pair_mdf-6.jpg](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 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 Making LAMMPS section for more info on packages.