A different strategy has been followed in Ref. 11 where it was proposed to first generate canonical orbitals localized on the monomers. In the second step, a configuration interaction singles (CIS) wave function is projected onto this localized basis to generate monomer and charge transfer states. They in turn are used to decompose the excited states of the supermolecule. Contrary to diabatization, approaches starting from interacting monomers are not limited by the requirement to perform supermolecule calculations. For instance, in a classic paper Krueger and Scholes calculated excitonic coupling in a light-harvesting protein by using the transition density cube method for evaluating the Coulomb integral of the transition densities 12 . Alternatively, an integral-direct approach with prescreening has been used for the calculation of the Coulomb couplings . An implementation based on spin-adapted configuration state functions (CSFs) has been proposed in Ref. 15. It includes a full CIS expansion of monomer excited states as well as exchange and non-orthogonality of the exciton basis. Often the coupling to thermal fluctuations of the vibrational degrees of freedom is described by means of molecular dynamics sampling of an equilibrium ensemble.