Smearing induced dynamical stability of NbN and MoN in rocksalt structure

The present paper reports a comprehensive first-principles calculation of electronic structure and lattice dynamical properties of niobium and molybdenum mononitrides in rocksalt phase at ground state as well as at finite electronic temperature applied using smearing parameter. The optimized structure with equilibrium parameters in rocksalt phase is dynamically unstable. An increase in smearing parameter or considering the finite temperature effects increases acoustic phonon frequencies at X point of the Brillouin zone and rocksalt structure dynamically stabilized for both compounds. This is because of the lowering of Fermi energy with increase of smearing parameter. Much better agreement between the calculated and experimental data is found as compared to previous calculations and a consistent description of the dynamical stability in the case of rocksalt phase of NbN and MoN is achieved. The thermodynamical functions are also calculated in the frame work of quasi harmonic approximation and discussed. (C) 2012 Elsevier B.V. All rights reserved.