The underlying theory of the FDE-diab approach will be briefly repeated here for the specific case of two non-covalently bound molecules A and B forming a radical cation complex [A • • • B] +• . This rather simple consideration has a direct connection to CT processes often occurring between two pigments in photosynthetic systems and is sufficient enough for dimeric molecular models presented in this work. Note, however, that generalization to multiple fragments is straightforward from a mathematical point of view. In these radical cation complexes, charge and spin are delocalized to some extent between both molecules. The spin-density ratio can range from a complete delocalization (i.e., 50%/50%) to a localization at only one fragment. The former case can be found in