Ab initio determination of lattice dynamics and thermodynamics of β - BC2N

Using the pseudopotential density functional method, an ab initio study has been performed to determine the lattice dynamics and thermodynamics of β-BC2N, including phonon dispersion, phonon density of states, and thermodynamic properties. A considerable energetic overlap between the LO-, TO-, and LA-phonons is revealed in the phonon dispersion. The total phonon density of states shows four main regions arising from different relative motions among the B, C1, C2, and N atoms. The calculation shows that β-BC2N has more vibration states in the low frequency region than diamond and hence, its heat capacity Cv is greater than that of diamond. The Debye temperature ΘD of β-BC2N, which determines the Debye stiffness, is found to be smaller and larger than those of diamond and c-BN, respectively.