As expected, at larger intermolecular separations [see Fig. (top)] spin-density distributions become more and more localized. The complete localization is observed at displacements ∆R ⊥ larger than 1.0 Å. This behavior is caused by the absolute magnitudes of the electronic coupling decreasing exponentially with the intermolecular separation. Interestingly, the calculated spin-density ratios for PSI, PSII, and BRC show a qualitatively different behavior at shorter distances. The inner pairs of PSI and PSII have more localized distributions at ∆R ⊥ = -0.5 Å than at the equilibrium distances.