First-principles energy band calculation for CaBi2O4 with monoclinic structure

The electronic structure of CaBi2O4 is calculated by a GGA approach. The valence band maximum is approximately located at the Γ-point or the Y-point and the conduction band minimum at the V-point. This means that CaBi2O4 is an indirect energy gap material. The conduction band is composed of Bi 6p–O 2p interaction. On the other hand, the valence band can be divided into two energy regions ranging from −9.92 to −7.40 eV (lower valence band) and −4.69 to 0 eV (upper valence band). The former is mainly constructed from Bi 6s states interacting slightly with O 2s and 2p states, and the latter consists of O 2p states hybridizing with Bi 6s and 6p states. The states near the valence band maximum are strongly localized and the mobility of holes generated by band gap excitation is predicted to be fairly low.