Which oxidation state is preferable at S0 state in oxygen-evolving complex, Mn4(II, III, IV, IV) or Mn4(III, III, III, IV)? A B3LYP study

► The electronic structures of the CaMn4O5 core are theoretically examined. ► Two different states of Mn4[III, III, IV, III] and Mn4[III, IV, IV, II] are obtained. ► Mn4[II, III, IV, IV] at the S0 state is ruled out. ► The geometries of the CaMn4O5 core are important. ► The patterns of the hydrogen-bonding networks of water molecules are also important.