Simulation of the electronic structure of simple oxides BeO and Si[O.sub.2] and complex oxides [Be.sub.2]Si[O.sub.4] and [Be.sub.2][Si.sub.x][Ge.sub.1-x][O.sub.4] with the phenacite structure

The ab initio numerical calculations of the electronic structure of simple oxides BeO and Si[O.sub.2] and complex oxides [Be.sub.2]Si[O.sub.4] and [Be.sub.2][Si.sub.x][Ge.sub.1-x][O.sub.4] with the phenacite structure have been performed using the electron density functional theory. The calculations indicate that the main feature of the systems under investigation is the presence of oxygen states in both the valence and conduction bands. The splitting of the bottom of the conduction band has been revealed in the electronic structure of the [Be.sub.2][Si.sub.x][Ge.sub.1-x][O.sub.4] system. The splitting width is about 1.5 eV. The main contribution to the formation of a narrow subband of the conduction band comes from the 2s and 2p states of oxygen and the 4d state of germanium. Microscopic models of the spatial localization of the electron density on lower energy states of the conduction band of oxide crystals have been developed using the Wannier function technique. The reflection spectra of BeO, Si[O.sub.2], and [Be.sub.2]Si[O.sub.4] have been analyzed. The reported calculations of the electronic structure imply the exciton nature of the 9.7-eV reflection peak in the [Be.sub.2]Si[O.sub.4] crystal.