Theoretical study of boron nitride modifications at hydrostatic pressures

This paper presents a detailed study of boron nitride modifications at hydrostatic pressures. Cohesive properties of zinc blende (c-BN), wurtzite (w-BN), hexagonal (h-BN), rhombohedral (r-BN), and rocksalt structure are calculated by systematic optimization of unit cell parameters and atomic positions using total-energy density-functional methods. With focus on the very rarely discussed layered modifications the p-V equations of states are derived. It is confirmed that the isothermal bulk modulus of the sp(2)-bonded phases is more than 10 times smaller in comparison to the dense phases. Additionally, the equilibrium line of c-BN and h-BN in phase p-T diagram is calculated. According to recent experimental reports c-BN is predicted as a stable modification at standard conditions.