First-principles studies of diamond polytypes

Using first-principles methods, we have performed a systematic investigation of the cubic, rhombohedral and hexagonal diamond polytypes, both in equilibrium and under hydrostatic pressure. For each of the diamond polytypes (2H, 3C, 4H, 6H, 8H, 9R, 10H-SiC form, 10H-ZnS form, 15R and 21R), the structural, energetic, and electronic properties are investigated. The calculated lattice parameters, mass densities and ground-state energies of the diamond polytypes show clear trends with their hexagonality, while bulk modulus and elastic parameters are rather insensitive to the hexagonality. It is found that there are no phase transitions between these diamond polytypes studied in this work, at a pressure range from 0 to 500 GPa. For the series of diamond polytypes studied, the calculated results indicate that the relationship between ground-state electronic band gap and hexagonality at zero pressure is different from that observed at the hydrostatic pressure of 500 GPa.