Global potentials for calcium and strontium solids

Empirical two- plus three-body potentials have been derived for calcium and strontium, and applied to the fee and bcc structures of both metals. The parameters are derived by fitting phonon frequencies, elastic constants and other structural data. The potentials obtained give a sensible ordering of solid structures, and good energy profiles along the (Bain) tetragonal distortion pathway between the fee and bcc allotropes. The potentials have been used to calculate the fee and bce phonon densities of states (DOS), from which the Helmholtz energies and the fee --> bcc transition temperatures (T-c) have been evaluated. We overestimate the value of T-c for Ca and underestimate it for Sr. The potentials give surface energies which are in good agreement with experiment.