THE TIGHT-BINDING APPROACH TO THE CORUNDUM-STRUCTURE D-COMPOUNDS

The analysis of electronic structures has been carried out for the transition-metal compounds showing the corundum-type crystal symmetry using the suggested tight-binding method for interacting bands. With the self-consistent field approximation, the branches of the electronic spectra and energy gaps have been analytically calculated. The role of the electron correlations was found to be decisive for the dielectrization of spectra for which no additional assumptions, e.g. the existence of spin- or charge-density waves, was necessary. The data obtained provide an explanation for the appearance of the insulator state in such compounds as Ti2O3, V2O3, Cr2O3, alpha-Mn2O3 and alpha-Fe2O3. The calculated values of band gaps agree reasonably with the experimental data available. The Peierls problem is solved for the corundum-structure d compounds.