Realizing the semiconducting state of delafossite AgFeO2 by GGA + U calculations

The electronic structures of delafossite-type oxide AgFeO2 have been calculated by using the full potential linearlized augmented plane wave (FP-LAPW) method within the generalized gradient approximation (GGA) and GGA + U. It was found that the GGA calculations lead to a metallic state for AgFeO2 which is in contradiction with the experiment that AgFeO2 is a semiconductor. By taking into account the Hubbard interaction parameter U, the GGA + U calculations produce a semiconducting state for AgFeO2 when U > 0.68 eV. An energy band gap which is the gap between the highest occupied valance band of Ag-3d and the lowest upper Hubbard band of Fe-3d was predicted to be 1.15 eV with an effective Ueff = 7.86 eV.