Energy Diagrams for Water Oxidation in Photosystem II Using Different Density Functionals

The full sequence of intermediates in the water oxidation process in photosystem II has recently been characterized by model calculations, in good agreement with experiments. In the present paper, the energy diagram obtained is used as a benchmark test for several density functionals. Only the results using B3LYP with 15% or 20% show good agreement with experiments. The other functionals tried show errors for some energy levels as large as 20-30 kcal/mol. The reason for these large errors is that the error for three consecutive oxidations of Mn(III) to Mn(IV) accumulates as the cluster is oxidized.