Wesolowski and coworkers investigated several aspects of such approaches for modeling solvent effects with FDE. First, different strategies for the choice of the solvent electron density were investigated. Humbert-Droz el al. explored the sensitivity of calculated shifts in excitation energies with respect to the choice of the frozen density ρ II for selected test cases of aromatic chromophores microsolvated by up to three water molecules. They found that a simple charge-weighted superposition of atomic densities leads to large variations in the excitation energies and strongly depends on the choice of atomic charges. The commonly used superposition of molecular electron densities (see, e.g., Refs. ) turned out to be more stable and only showed a weak dependence on the basis set. Finally, the use of a frozen density from a single KS-DFT calculation for the solvent environment was also considered. Different strategies for including the polarization of the solvent molecules are compared in Ref. . An alternative to using a computed frozen density is explored in Ref. . Here, crystal structures of complexes of glycine dipeptide with a single solvent molecule were considered, and the frozen solvent density was extracted from the X-ray diffraction data, i.e., an "experimental" electron density was used as ρ II .