Electronic structure of bulk- and Na-intercalated TiS2 determined from a GGA plus U study with the Hubbard terms obtained ab initio

A theoretical study on the electronic structure of titanium sulfide compounds TiS2 intercalated with Na is presented using generalized gradient approximation (GGA)+U calculations. Na-intercalated TiS2 compounds are well-known materials in the field of battery systems. The atomic structure of available experimental ultraviolet photoemission spectroscopy (UPS) data is discussed and modeled on a Na3Ti12S24 unit cell. The on-site effective correlation term U is determined from first principles following a linear-response method for the Ti 3d electrons of this compound and the corresponding host TiS2. Valence electronic structures obtained from subsequent GGA+U calculations are compared to experimental UPS available data and to standard GGA results for both compounds. The improvement achieved with the ab initio GGA+U method and the agreement with the experimental spectra are discussed.