Hybrid QM/QM Study of Electronic d-d Spectra of Trivalent Transition Metal Oxides.

Transition metal oxides have been traditionally studied in theoretical chemistry and solid-state physics as they reflect the complexity of the electronic structure of materials with open d -shells. The complex electronic structure stems from the presence of strong correlations of both static and dynamical nature which are characteristic of open shell d -electrons. Systematic and computationally efficient account for correlation effects in transition metal compounds is a key challenge in theoretical chemistry. Hybrid electronic structure methods represent a promising way to address this problem. In this work, we apply a hybrid QM/QM method-periodic Effective Hamiltonian of Crystal Field (pEHCF)-to study multiplet structure of open d -shells in a series of trivalent and mixed-valence oxides: α -Fe2O3, α -Mn2O3, Cr2O3 and Co3O4. The calculated energies of the excited d -multiplets are compared with available experimental optical spectroscopy data. Our calculations clarify the interpretation of spectroscopic lines observed in experiments for two challenging systems: Fe2O3 and Co3O4. Furthermore, we assess the overall performance of pEHCF for transition metal oxides and place our results in a more general context by comparing them with previous studies that used different electronic structure methods.