Electronic structure of silver chalcogenides investigated by hard x-ray photoemission spectroscopy and density functional theory calculations

We have investigated the electronic structure of silver chalcogenides Ag2 X ( X = S, Se, Te) and their solid solutions using hard x-ray photoemission spectroscopy in combination with density functional theory calculations using generalized gradient approximation (GGA). By including the corrections for on-site Coulomb interactions (GGA + U), we successfully reproduced the valence band photoemission spectra, which consist mainly of the Ag 4 d band, by calculation. The estimated values for U = 4–6 eV are slightly high for Ag 4 d electrons but are consistent with those used in previously reported structural studies. On the other hand, the magnitude of the energy gap is virtually independent of U. These results suggest the strong correlation between Ag 4 d electrons in Ag2 X compounds to have surprisingly little impact on their electron transport properties.