Practically, the projection can be performed, and here we examine the effect on frequencies, IR intensities, and Raman intensities for the seven solute-solvent systems. The results for the six solute-solvent systems where only the solute molecule is in the QM subsystem are presented in Figure , while the results for formaldehyde in water with and without two solvent molecules in the QM subsystem are presented in Figure . Here, we investigate the absolute differences in frequencies, as well as the relative and normalized absolute differences in IR and Raman intensities. The normalized absolute differences refer to normalizing the absolute differences by the maximum absolute difference across all modes except the six lowest ones. Figures 1 and 2 also include the pseudo-translational and pseudo-rotational contributions to all normal modes calculated using eqs 4 and 5, respectively.