Structural calculations for bulk As

Abstract

The valence-electron contribution to the total energy of simple-cubic and rhombohedral arsenic has been calculated with use of local-density-functional theory and a scalar-relativistic version of the linear augmented-plane-wave method. The results at normal pressure show that the observed rhombohedral (A7) structure is favored energetically over the cubic phase by about 0.07 eV/atom. The calculated values for the lattice parameter (a=4.084 Å), rhombohedral angle (α=55.9°), and internal displacement parameter (u=0.2294) are in excellent agreement (∼0.3%, 2%, and 0.8%, respectively) with experiment. The cubic-rhombohedral energy difference, which is due to a Peierls-type mechanism at normal volume, is found to decrease at reduced volumes, leading to a stable high-pressure (∼190 kbar) cubic phase for V/$V_0$≲0.8. .AE