Analyzing the results from Figs. and, a number of conclusions can be drawn. all, as can be seen from the spin densities of the non-modified structures (∆θ = 0 • and ∆R = 0 Å), FDE-diab leads to strongly localized spin-density distributions. These localized spin densities are expected for this type of molecular systems and are in qualitative agreement with experimental measurements. The possibility to obtain such distributions with the rather simple non-hybrid GGA-type PW91 approximation points to the fact that FDE-diab essentially avoids the consequences of the self-interaction-error, as far as intermolecular phenomena are concerned (as has already been highlighted in Refs. and ). In addition, FDE-diab does not lead to overestimated areas of negative spin density, in contrast to conventional KS-DFT calculations with hybrid functionals. The FDE-diab spin-density distributions are highly sensitive to modifications of the molecular structure (as can be seen from Fig. ), while the spin density obtained with, e.g., M06-HF does not show any such dependencies. All of this makes FDE-diab a valuable tool for spin-density calculations with distinct advantages over the standard KS-DFT approach. Secondly, the FDE-diab calculations conducted here partially support the hinge-type model for the RC of PSII. The spin densities obtained for the deprotonated models are, indeed, dependent on the angle θ between the His molecule and the pyrrole ring D of Chl. In line with the interpretation provided in Ref. , the angle tilt towards the ring D causes a larger overlap between MOs of Chl a and His (for overlap values, see