Structural, phonon and thermodynamic properties of fcc-based metal nitrides from first-principles calculations

Structural, phonon, and thermodynamic properties of fcc-based metal nitrides MN (M=Ti,Al,Zr,Hf) have been investigated by first-principles calculations within the local density approximation (LDA) and the generalized gradient approximation (GGA). The supercell method for lattice dynamics is utilized to calculate the phonon density of states, and the thermodynamic properties (heat capacity, enthalpy, entropy, and Gibbs energy) of these nitrides at elevated temperatures are predicted via the quasiharmonic approximation. We find that the lattice parameters predicted by GGA agree well with experiments compared to those from LDA. The GGA predicts a larger bond length and a smaller bulk modulus than those from LDA. It is found that the vibrational contribution to Gibbs energy is larger for HfN in comparison with other metal nitrides due to its higher population of phonon density of state in the low frequency region. Calculated structural, phonon, and thermodynamic properties are in good agreement with the available experiments and CALPHAD-type evaluations.