Interpretation of the optical absorption spectrum of Co3O4 with normal spinel structure from first principles calculations

First principles calculations based on density functional theory have been employed to study the electronic, magnetic and optical properties of Co₃O₄ in a cubic normal spinel structure. Exchange and correlation effects between electrons were treated by a B3PW91 hybrid functional, which produced better results than others scheme, such as GGA+U or PBE0 hybrid functionals or mBJ semilocal potential. The work focuses on clarifying the nature of the optical absorption bands, which have motivated various theoretical and experimental works in the literature. The calculated optical absorption spectrum was compared with available experimental data. On the basis of this calculated electronic and magnetic structure, the optical absorption peaks (theoretical and experimental) could be satisfactorily explained in terms of d3d   charge transfer transitions between both CO²⁺${\mathrm{CO}}^{2^{+}}$→CO²⁺${\mathrm{CO}}^{2^{+}}$ and CO³⁺${\mathrm{CO}}^{3^{+}}$→CO³⁺${\mathrm{CO}}^{3^{+}}$ ions. The calculations also predicted that the crystal field splittings at both octahedral and tetrahedral sites in the Co₃O₄ compound are of the same magnitude.