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:

$\displaystyle E = \sum_{i<j} \left[ {q_iq_j\over r_{ij}} e^{-\gamma r_{ij}} + A_{ij}e^{-r_{ij}/\rho_{ij}} \right]. $

The parameters that can be specified with PARAMS are $ \gamma$, the magnitude of the ionic charges, a single value of $ \rho$, 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 $ \gamma$. Atomic units are assumed. Subroutines used: ions.

David Wales 2017-09-21