| SERS has been widely used in studying the interaction mechanisms of molecules with the surface of a substrate and molecular orientation. However, with the variation of the characteristics of the surface of the substrates, the SERS spectrum of adsorbates will also be different, which causes the analyses difficult. The common analytical method is on the basis of the shift of Raman bands, enhancement or weakening of intensity to hypothesize the adsorption orientation, geometry configuration, and adsorption essence of adsorbates on the surfaces of substrates. Because SERS is found to be affected by many factors such as the different SERS substrates, surface configuration, structure, temperature, and even PH value and so on, the veracity of such a guess has often prevented researchers from making definite conclusions. The rationality of adsorption models and relevant theory cannot effectively be examined, which leads to many difficulties in the research of SERS mechanisms and the application of SERS technology.Theoretically, the difficulty lies in the establishment of a straightforward model, which should describe the combination of substrate and the adsorbed molecule properly, and at the same time can be made use of calculating the vibrational spectra easily.However, quantum chemically, one can tackle the problem in two different ways, the first approach being periodic density functional theory (DFT) and the second one using a finite cluster model of the surface studied. In this paper, we used the first approach. The calculations based on DFT have been used in many areas; the results are also in good agreement with the experimental results in calculating vibrational frequencies.We adopt n-hydroxybenzoic acid and n-Aminobenzoic Acid(n=P, M, O) molecules as probes, and apply IR Raman to detecting the molecules' adsorption behaviors on metalnanoparticles. The results of comparing the experimental and theoretical outcome are satisfied.
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