pair_style born/coul/long/cs command
pair_style buck/coul/long/cs command
pair_style born/coul/dsf/cs command
pair_style style args
- style = born/coul/long/cs or buck/coul/long/cs or born/coul/dsf/cs
- args = list of arguments for a particular style
born/coul/long/cs args = cutoff (cutoff2) cutoff = global cutoff for non-Coulombic (and Coulombic if only 1 arg) (distance units) cutoff2 = global cutoff for Coulombic (optional) (distance units) buck/coul/long/cs args = cutoff (cutoff2) cutoff = global cutoff for Buckingham (and Coulombic if only 1 arg) (distance units) cutoff2 = global cutoff for Coulombic (optional) (distance units) born/coul/dsf/cs args = alpha cutoff (cutoff2) alpha = damping parameter (inverse distance units) cutoff = global cutoff for non-Coulombic (and Coulombic if only 1 arg) (distance units) cutoff2 = global cutoff for Coulombic (distance units)
pair_style born/coul/long/cs 10.0 8.0 pair_coeff 1 1 6.08 0.317 2.340 24.18 11.51 pair_style buck/coul/long/cs 10.0 pair_style buck/coul/long/cs 10.0 8.0 pair_coeff * * 100.0 1.5 200.0 pair_coeff 1 1 100.0 1.5 200.0 9.0 pair_style born/coul/dsf/cs 0.1 10.0 12.0 pair_coeff * * 0.0 1.00 0.00 0.00 0.00 pair_coeff 1 1 480.0 0.25 0.00 1.05 0.50
The styles with a coul/long term are identical to the pair_style born/coul/long and pair_style buck/coul/long styles, except they correctly treat the special case where the distance between two charged core and shell atoms in the same core/shell pair approach r = 0.0. This needs special treatment when a long-range solver for Coulombic interactions is also used, i.e. via the kspace_style command.
More specifically, the short-range Coulomb interaction between a core and its shell should be turned off using the special_bonds command by setting the 1-2 weight to 0.0, which works because the core and shell atoms are bonded to each other. This induces a long-range correction approximation which fails at small distances (~< 10e-8). Therefore, the Coulomb term which is used to calculate the correction factor is extended by a minimal distance (r_min = 1.0-6) when the interaction between a core/shell pair is treated, as follows
where C is an energy-conversion constant, Qi and Qj are the charges on the core and shell, epsilon is the dielectric constant and r_min is the minimal distance.
The pair style born/coul/dsf/cs is identical to the pair_style born/coul/dsf style, which uses the the damped shifted force model as in coul/dsf to compute the Coulomb contribution. This approach does not require a long-range solver, thus the only correction is the addition of a minimal distance to avoid the possible r = 0.0 case for a core/shell pair.
These pair styles are part of the CORESHELL package. They are only enabled if LAMMPS was built with that package. See the Making LAMMPS section for more info.