First principles calculation of the lattice constants of hexagonal and cubic boron nitride to 3000 K and 30 Gpa

The lattice constants of hexagonal and cubic boron nitride at the range pressure of 0–30 GPa and at the range temperature of 0–3000 K are calculated by ultra-soft Vanderbilt with the local density approximation (USPP_LDA) and the projector-augmented wave with generalized gradient approximation (PAW_GGA) respectively. Good agreement is achieved between the theoretical and experimental results in lattice constants of hexagonal and cubic boron nitride at a given temperature and pressure. In this work, USPP_LDA is more suitable to calculate lattice constants of hexagonal boron nitride, while PAW_GGA has higher accuracy in the calculation of lattice constants of cubic boron nitride. The theoretical results of lattice constants of c-BN have more accuracy than those of h-BN with increasing pressure using both PAW_GGA and USPP_LDA methods.