Electronic Structure and Bonding in Co-Based Single and Mixed Valence Oxides: A Quantum Chemical Perspective.

The mixed valence cobalt oxide, Co3O4, is a potential candidate as a photovoltaic (PV) material, which also exhibits intriguing chemical and catalytic properties. Here, we present a comparative study of the electronic, magnetic, and chemical bonding properties of mixed valence Co3O4 (i.e., Co2+/3+) with the related single valence CoO (i.e., Co2+) and Co2O3 (i.e., Co3+) oxides using density functional theory (DFT). We have employed a range of theoretical methods, including pure DFT, DFT+U, and a range-separated exchange-correlation functional (HSE06). We compare the electronic structure and band gap of the oxide materials, with available photoemission spectroscopy and optical band gaps. Our calculations suggest that the bonding between Co3+ and O2– ions in Co2O3 and Co3O4 and Co2+ and O2– ions in CoO and Co3O4 are rather different. We find that Co2O3 and Co3O4 are weakly correlated materials, whereas CoO is a strongly correlated material. Furthermore, our computed one-electron energy level diagrams reveal ...