Syntax:
pair_style lj/smooth Rin cutoff
Examples:
pair_style lj/smooth 8.0 10.0 pair_coeff * * 10.0 1.5 pair_coeff 1 1 20.0 1.3 7.0 9.0
Description:
Style lj/smooth computes a LJ interaction with a force smoothing applied between the inner and outer cutoff.
The polynomial coefficients C1, C2, C3, C4 are computed by LAMMPS to cause the force to vary smoothly from Rin to Rc. At Rin the force and its 1st derivative will match the unsmoothed LJ formula. At Rc the force and its 1st derivative will be 0.0.
IMPORTANT NOTE: this force smoothing causes the energy to be discontinuous both in its values and 1st derivative. This can lead to poor energy conservation and may require the use of a thermostat. Plot the energy and force resulting from this formula via the pair_write command to see the effect.
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:
The last 2 coefficients are optional. If not specified, the global Rin and cutoff are used. Rin cannot be 0.0. If Rin = cutoff, then no force smoothing is performed for this type pair; the standard LJ formula is used.
Mixing, shift, table, tail correction, per-atom energy/stress, restart, rRESPA info:
For atom type pairs I,J and I != J, the epsilon, sigma, Rin coefficients and the cutoff distance for this pair style can be mixed. Rin is a cutoff value and is mixed like the cutoff. The other coefficients are mixed according to the pair_modify mix option. The default mix value is geometric. See the "pair_modify" command for details.
This pair style supports the pair_modify shift option for the energy of the pair interaction.
The pair_modify table option is not relevant for this pair style.
This pair style does not support the pair_modify tail option for adding long-range tail corrections to energy and pressure, since the energy of the pair interaction is smoothed to 0.0 at the cutoff.
This pair style can calculate per-atom energy and stress, as used by the compute epair/atom, compute stress/atom, and dump custom commands.
This pair style writes its 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.
This pair style can only be used via the pair keyword of the run_style respa command. It does not support the inner, middle, outer keywords of the run_style command.
Restrictions: none
Related commands:
Default: none