Relativistic effects on the structural phase stability of molybdenum

The relative stabilities of the fee, bcc, and hcp structures of molybdenum (Mo) are studied as functions of volume with both nonrelativistic and scalar-relativistic linear combinations of Gaussian-type orbitals (LCGTO) fitting function calculations. Relativity is shown to have a significant effect on the bcc-fce structural energy difference that first increases, then decreases, with pressure, but has only a negligible effect on the hcp-fcc structural energy difference. The scalar-relativistic bcc-fcc energy difference curve obtained here is in good agreement with an earlier fully relativistic calculation using the all-electron full-potential linear muffin-tin orbital method. Unlike previous theoretical work, this investigation finds no region of hcp phase stability at T = 0. Instead, the bcc phase transforms directly into the fee phase at a pressure of about 6.6 Mbar.