Calculations of the orbital similarity are performed as suggested in our previous paper. Orbital similarity is computed between donor HOMO and D-A dimer HOMO, as well as acceptor LUMO and D-A dimer LUMO, where values of orbital similarity range between 0 (no similarity) and 1 (same orbital). Donor and acceptor geometries are taken to be the geometries they assume in the optimized D-A dimer complex (i.e. donor and acceptor geometries are not geometric minima of the isolated molecules), allowing for the simplification that the overlap matrix of atomic basis functions between donor and D-A complex (as well as acceptor and D-A complex) is equivalent to the self-overlap of atomic basis functions, reported in the output of our electronic structure calculations.