The structural stability of the rhombohedral and simple cubic phases is studied for the group-VA elements. Using an ab initio pseudopotential total-energy method, the calculated phonon frequencies for the longitudinal acoustic mode at the corner of the simple-cubic Brillouin zone are found to soften. This suggests that all group-V elements are likely to form in the rhombohedral structure with respect to the simple cubic phase. At high pressures, the rhombohedral stability is diminished, causing a transition to the simple-cubic structure.

• Received 24 February 1986

DOI:https://doi.org/10.1103/PhysRevB.33.7371