Theoretical Investigation of Metallic Phase of the Group V Crystals under Pressure.

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The total energies of the rhombohedral A7 and the simple cubic (SC) phase for phosphorus (P), and those of the SC and the body centered (BCC) phase for arsenic (As) and antimony (Sb) are calculated within the local-density functional formalism by using the norm conserving pseudopotentials.1. The calculated results for P succesfully explain the phase transition from the A7 to the SC phase under pressure. The calculated electronicstructure of the metallic SC phase reveals that the bonding in this phase has an appreciable amount of covalency. It is also found that the stabilization of the SC structure under pressure is due to the fact that the cotribution of the electrostatic energy to the compression. Moreover, it is shown that the absence of the core d-orbitals of a P atom is very important in explaining thdifference between P and other 5B elements in the phase transition under pressure.2. Calculated equations of state for the SC-As and the BCC-Sb are in exellent agreement with the experimental ones. In order to see the difference between the phase transitions for both elements, the total energies are also calculted for hypothetical pseudopotentials, which are so constructed as to have an s (or p) level between As's and Sb's one. It is shown that the difference is mainly due to the p level.