\(\renewcommand{\AA}{\text{Å}}\)
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 * * 1.0 1.0
pair_coeff 1 1 1.1 2.8 3.0 3.2
pair_style buck/mdf 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 * * 1.0 1.0
pair_coeff 1 1 1021760.3664 2120.317338 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.
The tapering, f(r), is done by using the Mei, Davenport, Fernando function (Mei).
where
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:
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. 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)
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:
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:
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)
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 shift option or long-range tail corrections to pressure and energy.
These 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.
These styles can only be used via the pair keyword of the run_style respa command. They do not support the inner, middle, outer keywords.
Restrictions
These pair styles can only be used if LAMMPS was built with the EXTRA-PAIR package. See the Build package doc page for more info.
Default
none
(Mei) Mei, Davenport, Fernando, Phys Rev B, 43 4653 (1991)