First-principles study of the stability of BN and C

First-principles total energy calculations are performed to study the phase stability of BN and C at low temperature. These are done using density functional theory (DFT) within the local density approximation (LDA) and the generalized gradient approximation (GGA). We find that for both materials LDA calculations predict dense cubic structures as the ground state structures, while the GGA calculations predict less dense hexagonal layered structures as the ground states. Our calculated results provide a stringent test for the validity of the functional used for the DFT calculations. Accurate experimental measurements of thermodynamic properties for BN and C at low temperature are needed to clarify the stability issues for these materials.