Ab initio determination of the bulk properties of MgO.

Ab initio periodic Hartree-Fock (HF) theory was used to determine the elastic constants and selected phonon frequencies of bulk MgO; the accuracy of a posteriori correlation corrections to the periodic Hartree-Fock calculations is also discussed. Inc)usion of difFuse atomic orbitals in the MgO basis was necessary to accurately describe elastic distortions and phonon vibrations of the solid. The computed HF lattice constant (4.195 A) agrees with experiment (4.19 A) and the elastic constants are within + 15% of the observed values. Correlation corrections to these energetics shorten the lattice parameter to 4.09 A and further stiffen the elastic constants. The HF phonon frequencies at the (I, X, and L) points in the Brillouin zone were within 15% of experiment and the correlation corrections softened the modes irnproving agreement with experiment. These data will be used to parametrize electrostatic shell models of MgO.