LOW-PRESSURE CRYSTALLINE PHASES OF LITHIUM

Systematic study of equilibrium and low-pressure crystalline phases in Li using the full-potential linearized augmented-plane-wave technique (as embodied in the code WIEN) gives hcp < fcc < bcc as the equilibrium energetic ordering. The equilibrium hcp phase stability is enhanced slightly by relaxation from the ideal c/a ratio. The first pressure-induced phase transition is hcp --> fcc at a compression of V/V0 = 0.79. These results confirm, in whole or in part, the predictions of all other studies of the low-pressure crystalline phase ordering of Li except for one. The one anomalous calculation [H. Bross and R. Stryczek, Phys. Status Solidi B 144, 675 (1987)] finds bcc to be the most stable phase up to a compression V/V0 almost-equal-to 0.28. That result is traced to a peculiar dependence of the total energy of bcc alkali metals upon the details of the Brillouin-zone scan used in the calculation.