Copper-intercalated TiS2: electrode materials for rechargeable batteries as future power resources.

We report results of first-principles total-energy calculations of structural and optical properties of the TiS(2) single crystals intercalated with copper. Calculations have been performed using an all-electron, full potential, linearized, augmented, plane-wave method based on density functional theory using generalized gradient approximation for the exchange correlation energy functional. To complete the fundamental characteristics of these compounds, we have calculated and analyzed their linear optical susceptibilities. We demonstrate the efficiency of using a full potential on the band structure, density of states, and the optical properties. We compare our results of the intercalated Cu in different sites and concentrations with the host TiS(2) compound to ascertain the effect of Cu intercalation on the electronic and optical properties. Our calculations have shown that the electronic and optical properties are influenced significantly by the location and concentration of the Cu intercalate in the host compound. The Cu-s and Cu-p bands are very broad and do not contribute much to the density of states. The density of states and the electron charge density show that all Ti-Ti and S-S bonds are basically of ionic character and that Ti-S bonds are of covalent character. No covalent electrons are found between Cu and S atoms; that is, no covalent bond exists between the Cu and S atoms. The Cu atoms are ionic in the intercalated compounds.