Ab initio investigation on structural, electronic and lattice dynamical properties of MgN and GdN crystals

The present paper reports a comprehensive study of structural, elastic, electronic and phonon properties of MgN and GdN compounds in its rocksalt phase by means of first principles density functional theory and use of pseudo-potentials within generalized-gradient approximation to the exchange correlation functional for all calculations except phonons in the case of GdN. The computed equilibrium lattice constant and mechanical properties for both compounds agree well with the available experimental and theoretical data. The electronic band structure calculation shows an ionic component along with the covalent like character and clear half-metallic nature in rocksalt GdN, while rocksalt MgN shows covalent like character. Spin-polarized calculation suggests that the MgN has a negligible magnetization while GdN shows significant magnetization at equilibrium lattice constant. The phonon dispersion curves, phonon density of states and allied properties are also calculated. Zone center phonon frequencies are in good agreement with experimental Raman spectra. The structures observed in Raman spectra can be attributed to phonons near the zone center due to the presence of defect or disorder and the combination of LO(L) and LA(L) phonons.