In

This is used to specify a shielded Born-Meyer potential binary ionic clusters with anions and cations having the same magnitude charge. The atoms must be in the order cation, anion, cation, anion, etc. The energy is:

20#20

The parameters that can be specified with PARAMS are 21#21, the magnitude of the ionic charges, a single value of 22#22, assumed to be the same for all interactions, and A₊₊, A_- and A_+-, in order. Default values for KCl are set for all parameters except 21#21.Atomic units are assumed. Subroutines used: ions.