ELECTRONIC AND STRUCTURAL-PROPERTIES OF BESE, BETE, AND BES - COMPARISON BETWEEN AB-INITIO THEORY AND EXPERIMENTS

We have used first principles total energy pseudopotential techniques to calculate the ground state properties and the relative stabilities of the high pressure phases of the beryllium chalcogenides BeSe, BeTe, and BeS. We study the energy-volume (E-V) relations of the zincblende , NaCl, CsCl, NiAs, and beta-Sn structures of these compounds. The com ponents of the stress tensor were also calculated and used in the stru ctural relaxation of the tetragonal and hexagonal phases. From the E-V curves of the structures considered and the Gibbs construction we fin d that these compounds transform under pressure from the zincblende st ructure (B3) to the NiAs structure (B8), and no further transitions ar e found. Our calculated values of the structural parameters and the B3 --> B8 transition pressure for BeSe and BeTe agree well with recent e xperimental results. Very little is known experimentally for BeS, and our results for this compound have a predictive character.