Ab initio lattice dynamics calculation of vibrational density of states and Raman active modes of the olivinemineral Ni2SiO4

Abstract

We present results of ab initio lattice dynamics calculations for the olivine mineralNi2SiO4 using first-principles improved approaches within the Kohn–Sham formulation of densityfunctional theory. Dispersion relationships, vibrational density of states and Raman shiftshave been evaluated using the direct method. The calculations are compared with datafrom inelastic neutron scattering and Raman spectroscopy experiments. Non-spin-polarizedcalculations lead to clear structural instabilities and discrepancies with the measurements.Magnetic effects are taken into account by including first spin-polarization and then also aHubbard term to describe correctly the strongly correlated character of the 3d electrons ofNi2+ ions. Results of these models are in excellent agreement with theobservations, indicating that the structural stability and dynamics ofNi2SiO4 depend strongly on the magnetic interactions, spin–lattice coupling and electroncorrelation. These calculations will be used to help separate phonon and spin contributionsin on-going studies of magnetic excitations.