This keyword specifies a Born-Mayer potential of the form

$\displaystyle E = \sum_{i<j}\left[ {q_i q_j\over r_{ij}} + A_{ij}\exp(-r_{ij}/\rho) \right]. $

The sum runs over all ions. Tosi-Fumi[68] parameters in atomic units should be entered after the Tosi keyword in the order $ A_{++}$, $ A_{--}$, $ A_{+-}$, $ \rho$. The ions are then specified using atom types PL and MI for plus and minus, respectively, and can be in any order. There need not be equal numbers of positive and negative ions. C6 dispersion coefficients can be optionally added with the keyword TOSIC6 c6pp c6mm c6pm, where c6pp, c6mm, and c6pm should be the values of the C6 parameters between positive ions, negative ions and positive and negative ions in atomic units. First order induction energy can be added with the keyword TOSIPOL alphap alpham damp where ALPHAP and ALPHAM are the cation and anion polarisabilities in atomic units and DAMP is the damping parameter, without which cold fusion is likely. Note that the Welch potential has been fitted to include ion polarisabilities and is described below.

David Wales 2017-09-25