Bacteriochlorophyll (BChl) dimers were constructed from a reduced BChl-like monomer as shown in Figure . Monomer geometry optimization has been performed using DFT with the B3LYP functional and the 6-31G(d) basis set, including the effect of an aqueous environment using the polarizable continuum model. The optimized BChl-like monomer was used for a single-point energy calculation at the SA-RASSCF/MS-RASPT2 level of theory . More specifically, we computed state-averaged restricted active space self-consistent field (SA-RASSCF) theory ground (S 0 ) and first excited singlet (S 1 ) states, using an active To additionally analyze the multiconfigurational character of the ground state wave function of the monomer we performed a single point energy calculation at the hybrid Coupled Cluster model CC2 49,50 level of theory using the program TURBOMOLE. This calculation used the cc-pVDZ basis set, 52,53 the resolution of identity method with auxiliary basis sets from the TURBOMOLE library, 54 and the frozen core approximation.