In principle, it should be possible to evaluate all three quantities that enter the Marcus rate from electronic structure methods. To account for the local and global environment, however, it is typically required to embed electronic structure methods into a classical environment model, as the size of realistic disordered systems at least on the order of several tens of nm exceeds the capabilities of explicit quantum chemistry methods. Besides such quantum-classical embedding, of the key challenges involved in the multiscale modeling approaches of this kind is to use quantum-chemistry methods that allow for an accurate prediction of various excited states involved in the dynamical processes. Especially for the conversion of charge-neutral excitations, e.g., after photo absorption from localized exciton (LE) to charge-transfer (CT) state as an example of a photoinduced electron transfer reaction, the energetics of both LEs and CTs need to be described on an equal footing. In this context, the use of many-body Green's functions Theory employing the GW approximation and the Bethe-Salpeter equation (BSE) has become attractive to model electronically excited states on top of a ground-state reference calculation typically performed on the level of densityfunctional theory (DFT). It was shown that GW -BSE provides an effective single-and two-particle picture with accurate energies of LE and CT states without the need for any adaptations. Previous work has also shown that the additional screening caused by the molecular environment strongly affects the energies (and also densities) of CT states, more so than those of LEs, and that this energetic stabilization is important for finding CT-LE energy differences ∆E LE-CT that are favorable for LE to CT conversion in organic solar cell materials. To fully treat the dynamical process of this conversion in the spirit of Eq. ( ) requires also the reliable determination of the respective non-adiabatic coupling elements J LE-CT .