Raman signals can be enhanced by the chemical enhancement and the electromagnetic enhancement. In the current QM/DIM scheme, we don't account for the intermolecular charge transfer (CT) effect, which may be partially responsible for the limited accuracy of the QM/DIM scheme for Raman spectral calculations, especially when the intermolecular distance is short. To check this effect, we calculated the amount of charges on pyridine molecule within the complexes as shown in Table .