Fig. demonstrates that, for the adsorbed configurations, QM/DIM predicts a 20 times enhancement for most of the Raman peaks due to electromagnetic enhancement. Both the theoretical calculation and experimental measurement yield a consistent result trend on the MNP-induced changes on the relative spectral intensities. For example, the gold nanoparticle makes the strongest Raman peak of 4,4 -BPy shift to 1678 cm -1 from 1336 cm -1 , the relative intensity at around 1024 cm -1 decrease, and the two Raman peaks in the 600-800 cm -1 range disappear. However, the QM/DIM predictions hardly alter the molecular vibrational frequencies while the experimental frequency shifts could be as large as 18 cm -1 . It is unsurprising because after the 4,4 -BPy is adsorbed on the MNP, the QM/DIM optimization yields a similar geometry as the gas-phase one, thus producing only small changes in the vibrational frequencies. This is in line with the Raman spectra of the Py cases. As shown in Table , the frequencies calculated by full QM and QM/DIM methods have similar values. The large frequency changes after molecule adsorbed on MNP come from geometry differences between Py gas-phase minimum and full QM optimized Py-Au 18 complex.