A first-principles study of the electronic structure of the sulvanite compounds

We have investigated by means of first-principles total energy calculations the electronic structure of the sulvanite compounds: Cu3VS4, Cu3NbS4 and Cu3TaS4; the later is a possible candidate as a p-type transparent conductor with potential applications in solar cells and electrochromic devices. The calculated electronic structure shows that these compounds are indirect band gap semiconductors, with the valence band maximum located at the R-point and the conduction band minimum located at the X-point. The character of the valence band maximum is dominated by Cu d-states and the character of the conduction band minimum is due to the d-states of the group five elements. From the calculated charge density and electron localisation function we can conclude that the sulvanite compounds are polar covalent semiconductors.