The effect of Mn oxidation state on metal core electron excitations in manganese dimers: A time-dependent density functional investigation

Time-dependent density functional theory (TDDFT) calculations have been performed on a series of manganese dimers with averaged metal oxidation states of 2.0, 2.5, 3.0, 3.5 and 4.0. The excitation energies and oscillator strengths of transitions within the Mn K-core edges have been determined. The theoretical edge energies reproduce the experimental correlation between the relative position of the Mn K-edge and the averaged Mn oxidation state extremely well. A comparison with the results obtained previously for Mn complexes with different ligand environments shows that TDDFT can be successfully applied to determine the relative edge energy differences between Mn systems, taking into account the various oxidation states of the metal and differences in ligand environment in a self-consistent manner. The accuracy of the calculated edge energies indicates that the methodology employed in the current study can be used to determine the oxidation states of Mn atoms in the Mn₄Ca cluster of photosystem II (PSII).