First-principles calculations of elastic constants of c-BN

The lattice parameters, elastic constants, bulk modulus and its pressure derivative of c-BN are calculated using a first-principles plane wave method with the relativistic analytic pseudopotential of the Hartwigen, Goedecker and Hutter (HGH)-type and the pseudopotential of Troullier-Martins (TM)-type in the frame of local density approximation, and the dependences of bulk modulus on temperature and on pressure are investigated by the quasi-harmonic Debye model. The Debye temperature and the thermal expansion coefficient of c-BN are also calculated. The results obtained are well consistent with the available experimental data and other theoretical results. At zero pressure, the thermal expansion coefficients are about 6.0×10−6 K−1 at T=1724K and 6.5×10−6 K−1 at T=1972K, respectively, consistent with the experimental data.