The stability of the simple cubic phase of phosphorus

The transition from the rhombohedral phase to the simple cubic phase of phosphorus under pressure is studied within the local density-functional formalism with use of the norm-conserving pseudopotential. The calculated transition pressure is 15.8GPa, which is in good agreement with the measured value, 10GPa. The bonding in the simple cubic phase is shown to be predominantly covalent. It is found that the instability of the simple cubic structure under low pressures is understood by a Peierls' instability, which is just the same as the case of arsenic. It is also shown that the mixing of atomic 3d-orbitals in the occupied states is important for stabilizing the simple cubic structure under high pressures.