A new theoretical approach for the electrical properties of TiX2 (X = S, Se, Te) phases with density functional calculations

The electronic structures of layered transition metal dichalcogenides TiX2 (X=S, Se, Te) have been studied with the Amsterdam Density Functional package for periodic systems (ADF-BAND). The accuracy of this algorithm to calculate the charge transfer between the chalcogens and the metal has been tested at different levels of approximation (local-density approximation, generalized gradient corrections of Becke-Perdew and Perdew-Wang, and quasirelativistic calculations). The total and partial density of states of the three compounds, as well as the crystal orbital overlap population analysis, have been used to rationalize the electronic structure of the systems. The present results show a significant pld-block band overlap for TiTe2, leading to a Te(Sp)-->Ti(3d) electron transfer and a metallic behavior. Conversely, owing to the redox competition between the metal and the chalcogens, TiS2 and TiSe2 are predicted to be a semiconductor and a semimetal respectively. These physical properties are discussed in terms of electron density displacement from the chalcogen to the titanium when going from TiS2 to TiTe2. The relativistic effects appear to have no significant influence on the global physical properties of these layered compounds, although they slightly reduce the Te(Sp)-->Ti(3d) electron transfer. (C) 1998 American Institute of Physics.