Global potentials for calcium and strontium solids
Abstract
Empirical two- plus three-body potentials have been derived for calcium and strontium, and applied to the fcc 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 fcc and bcc allotropes. The potentials have been used to calculate the fcc and bcc phonon densities of states (DOS), from which the Helmholtz energies and the fcc → bcc transition temperatures (Tc) have been evaluated. We overestimate the value of Tc for Ca and underestimate it for Sr. The potentials give surface energies which are in good agreement with experiment.
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