Ab initio lattice dynamics of MnO.

Vibrational dynamics of the MnO lattice has been studied using density functional theory combined with the direct method. Considerations have been limited to the harmonic approximation. Ab initio calculated Hellmann-Feynman forces were used to obtain density of states and the dispersion relations of phonons in the MnO crystal. Corrections for the local Coulomb interactions were applied. The Hubbard energies were varied from 1 to 7.9 eV. Increased Hubbard terms give a significant increase in the on-site force constants of cations, while the force constants on anions are affected indirectly. The density of phonon states and the dispersion curves are shifted to higher frequencies with the increasing Hubbard energies. The on-site Coulomb interactions influence mainly the optical phonon vibrations. The higher Hubbard terms lower the mean-squared vibrations of both cations and anions. The lattice contribution to the heat capacity experiences small changes upon variation of Coulomb repulsion. Results of the calculations are compared to the existing experimental data.