Theoretical study of high-density phases of covalent semiconductors. II. Empirical treatment

We show that a simple pairwise model for covalent materials provides a good description of the high-density fourfold-coordinated metastable phases BC8 and ST12, in agreement with experimental results and ab initio calculations. We use this potential to study the high-pressure behavior and the free energy. We find that both phases are metastable at all temperatures. The relative energetic stability depends on the parametrization, but the ST12 phase has higher entropy. We therefore conclude that with correct pressure and temperature treatment it may be possible to synthesize ST12 as a new high-density metastable phase in Si.