Analysis of hydration effect based on standard redox potential of metals calculated by density functional theory combined with the reference interaction site model

We present calculations of the standard redox potentials (SRPs) for eight metal ions by employing density functional theory combined with an effective screening medium and a reference interaction site model (RISM). To calculate the SRP of metal ions, the primary hydration water molecules around metal ions are treated by using quantum mechanics (QM) or RISM. The SRPs calculated in the QM treatment are in good agreement with the experimental data. However, the SRPs calculated in the RISM treatment, where the universal force field (UFF) is employed, do not reproduce the experimental data quantitatively. We show that ion-water distances are overestimated in the RISM treatment and that the errors of the ion-water distances are correlated with the errors of the SRPs. Finally, we consider that one of the reasons for these errors in the RISM treatment is the overestimated repulsive potential of the UFF. Graphic abstract