For calculating the LE and CT densities of states, C 60 molecules are selected which are approximately in the first neighbor shell around one rubrene molecule. Given the conformation of this low-donor content materials, the behavior of this shell of molecules should be representative of the overall behavior of the material. After selection, polarizable GW -BSE/MM embedding calculations as described in Section 2.2 are performed for all dimers formed by rubrene and fullerene. Specifically, we employ for the GW -BSE calculations the def2-tzvp basis set with an optimized auxiliary basis for the steps including resolution-of-identity.