The spin-density ratios calculated for the isolated inner pair were equal to about 80%/20% and 76%/24% in favor of the P D1 co-factor for the trucated and non-truncated models, respectively. Inclusion of the nearby protein environment led to even more delocalized distribitions with the spin-density ratio of 65%/35% in favor of P D1 . These results are in good agreement with the experimental ENDOR measurements predicting 82% of spin to be localized on P D1 . Taking into account large electronic couplings between the inner pair co-factors, we can assume that the remaining spin density is probably localized at the P D2 molecule. This, however, contradicts the hinge-type model for the RC in PSII suggested in Ref. and suggests the delocalization of the spin-density distribution between P D1 and the axial His molecule. Calculations of spin-density ratios between two axial His molecules and the inner pair require the use of MOs of all four molecules in the diabatic-states construction procedure, and are not possible in terms of two-state models. This requires a generalization of the FDE-diab approach to multiple electronic states. Although most of experimentally measured spin-density populations of the P D1 co-factor in PSII were successfully reproduced by us in FDE-diab calculations of large protein binding pockets, the proposed strong asymmetry in the spin-density pattern was also not observed.