Calculation of Magnetic Properties and Spectroscopic Parameters of Manganese Clusters with Density Functional Theory

Abstract

Recently, the fundamental structures of the oxygen-evolving complex (OEC) in photosystem II were revealed with the X-ray diffraction experiment. Next problems are elucidation of the protonation mode and oxidation states of OEC that are key points for the oxidation reaction in the OEC. Comparison between electron paramagnetic resonance experimental results and ab initio computational results for the hyperfine coupling constants (HFCs) is helpful to determine them. Although the calculated HFC values strongly depend on the approximated exchange–correlation (XC) term of the ab initio density functional theory (DFT) method, there is little investigation on XC dependence of calculated HFC values. Thus, in this study, we have examined the accuracy of contemporary functionals, which are known to be efficient to describe magnetic interactions and molecular interactions, with implementing a benchmark test of HFCs. For this purpose, we constructed a test set consisting of nine dinuclear Mn complexes and Mn(II) ion ligated with six H2O molecules. The computational results are discussed in relation to nature of XC functionals.