Ab initio and semiempirical calculations of H^- centers in mgo crystals

The atomic and electronic structure of (Formula presented) ions substituting for (Formula presented) ions in regular sites in MgO crystals are calculated using an ab initio Hartree-Fock (HF) cluster approach and its semiempirical version, intermediate neglect of the differential overlap. The theoretical optical absorption energy is predicted to be 10 eV, which is supported by analysis of experimental data for the (Formula presented) centers in a series of ionic crystals. The HF simulations of (Formula presented) ion diffusion via direct interstitial hops along the [100] axis predict an activation energy of about 3 eV.