The electronic structure and chemical bonding in rare earth chalcogenides according to the Xα SW method—I: EuO,EuS and EuSe

Calculations of the electronic structure for (EuO₆)^10? (EuS₆)^10?, and (EuSe₆)^10? clusters, which represent the nearest-neighbour sphere surrounding Eu in EuO, EuS, EuSe, have been made by the Xα SW method. The contour maps for valence MO's have been drawn. The MO energy diagrams are in reasonable agreement with experimentally derived band structures. In spite of the localized nature of 4f-derived states, there are noticeable admixtures of 4f-states to the valence band. The 5d Eu states hydridize with the chalcogenide valence states, and the covalency of the chemical bonding decreases from EuO to EuSe, which can explain the decrease of elastic modulus, microhardness and chemical stability.