GLOBAL POTENTIALS FOR CALCIUM AND STRONTIUM SOLIDS

Empirical two- plus three-body potentials have been derived for calciu m and strontium, and applied to the fee and bcc structures of both met als. The parameters are derived by fitting phonon frequencies, elastic constants and other structural data. The potentials obtained give a s ensible ordering of solid structures, and good energy profiles along t he (Bain) tetragonal distortion pathway between the fee and bcc allotr opes. The potentials have been used to calculate the fee and bce phono n densities of states (DOS), from which the Helmholtz energies and the fee --> bcc transition temperatures (T-c) have been evaluated. We ove restimate the value of T-c for Ca and underestimate it for Sr. The pot entials give surface energies which are in good agreement with experim ent.