X-ray emission spectra and electronic structure of TiS2

Abstract

A characteristic structural feature of these compounds is the presence of close-packed layers, each of which represents a sandwich of two layers of atoms of the chalcogen (X), separated by a layer of atoms of the metal (M). The layers of the MX2 sandwiches are joined to one another by weak.van der Waals forces, so that these compounds can show intercalation, that is, the introduction of other aton;s or molecules into the spaces between the layers [3]. By introducing atoms or molecules of different types, iris possible to control the electron density in the layers, and hence to produce directed changes in the physical properties of these compounds. For example, the intercalation of the semiconducting dichalcogenides of transition metals of subgroups IV and VI has led to the appearance of metallic conductivity and even superconductivity at low temperatures [4, 5]. A large number of theoretical studies of the electronic structure of these compounds have been carried out by the methods of zone theory (see for example [6]). Zone methods are not suitable, however, for studying real crystals which show deviations from three-dimensional periodicity or which contain defects of different kinds or inserted atoms or molecules, or for studying intercalated compounds. A convenient method for studying the electronic structure of crystals with breakdown of translational symmetry is provided by cluster quantum-chemical calculations (see for example [7]). In this case, however, a number of problems arise, associated with the optimum choice of the cluster and allowance for the boundary conditions and methods used to carry out the self-consistent calculations. The present paper discusses the problem of the choice of the cluster in layer compounds for the case of the calculation of the electronic structure of TiS2. We previously obtained