Similar to the case of PSII, deprotonation at the axial His molecule of bacterial RC led to noticeable delocalizaton of the spin density for acute angles between His and D A . Thus, spin-density ratios of isolated truncated and non-truncated hinge models at ∆θ = -15 degree were both equal to 16%/84% in favor of His. It is, however, accepted that the axial His molecule in the bacterial RC does not have spin-density contributions. Therefore, taking into account the large degrees of spin-density localizations at the His residue for deprotonated models calculated with FDE-diab, one might conclude that the axial His from the bacterial RC most likely appears to be protonated. This agrees well with available experimental results .