Quantum chemical study of the nature of the ground state and the pressure-induced spin transition in CaFeO3

Ab initio calculations have been performed to clarify the character of the electronic ground state of the high-temperature phase of CaFeO3 at different external pressures. The analysis of the correlated N-electron wave function of properly embedded FeO6 clusters in terms of optimal atomic orbitals clearly establishes the character of the ground state as being dominated by charge transfer configurations. For all pressures, the number of Fe 3d electrons is around 5 and iron should be considered as a Fe3+ ion. We find an S = 2 to S = 1 transition around 25 GPa in the CaFeO3 crystal.