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 Functi onal package for periodic systems (ADF-BAND). The accuracy of this alg orithm to calculate the charge transfer between the chalcogens and the metal has been tested at different levels of approximation (local-den sity approximation, generalized gradient corrections of Becke-Perdew a nd Perdew-Wang, and quasirelativistic calculations). The total and par tial 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 signi ficant pld-block band overlap for TiTe2, leading to a Te(Sp)-->Ti(3d) electron transfer and a metallic behavior. Conversely, owing to the re dox competition between the metal and the chalcogens, TiS2 and TiSe2 a re predicted to be a semiconductor and a semimetal respectively. These physical properties are discussed in terms of electron density displa cement from the chalcogen to the titanium when going from TiS2 to TiTe 2. The relativistic effects appear to have no significant influence on the global physical properties of these layered compounds, although t hey slightly reduce the Te(Sp)-->Ti(3d) electron transfer. (C) 1998 Am erican Institute of Physics.