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The static structural properties and B1-B2 phase transition of SrO were calculated at an ab initio level within the Hartree-Fock (HF) approximation using the effective core potential. The HF data were corrected a posteriori by integrating the HF charge density according to the correlation---only gradient-density-functional formulas proposed by Colle and Salvetti [Theor. Chim. Acta 37, 329 (1975)] and by Perdew [J. P. Perdew, Electronic Structure of Solids, edited by P. Ziesche and H. Eschring (Akademie Verlag, Berlin, in press)]. The HF binding energy, structural parameters, lattice parameter, bulk modulus, and elastic constants are in reasonable agreement with experiment. The correlation correction brings the binding energy into better agreement with the experiment. The transition pressure between B1 and B2 phases is in good agreement with the experimental value at the HF level, whereas it is corrected poorly by the addition of an a posteriori correlation correction.

Three different crystal phases of magnesium oxide [B1 (NaCl), B2 (CsCl), and B${8}_{1}$ (inverse NiAs)] are investigated theoretically. An ab initio all-electron linear combination of atomic orbitals Hartree-Fock approximation is adopted; extended basis sets are used which have been variationally optimized in each case. In ordinary conditions, the B${8}_{1}$ and B2 structures result less stable with respect to the rocksalt structure by 0.44 and 1.77 eV, respectively. With increasing pressure, the transition B1\ensuremath{\rightarrow}B2 is estimated to occur around 2.2 Mbar, while it is not excluded that a pressure interval exists around 2 Mbar where the B${8}_{1}$ phase is the most stable of the three structures. Data on the electronic properties of the three phases are provided and discussed: Mulliken populations, charge-density distribution, electron momentum distribution and anisotropy, magnesium core deformation, and band structure.