First-Principles Simulation of Raman Spectra of Adsorbates on Metal Surfaces.

A general method is proposed to simulate the Raman spectra of adsorbates on metal surfaces. This method is based on an electrostatic-corrected cluster model with additional charges to compensate the loss of coordination of metal atoms, and an external field added to simulate the surface dipole and to reproduce the charge distribution obtained from periodic calculations. As a result, it is possible to couple the phonon calculation with the Raman tensors computed by this corrected cluster model to simulate the Raman spectra of the adsorbates on metal surfaces. In doing so, it is possible to overcome both the infinite dielectric constant of the ideal metal, which makes calculating Raman spectra with current periodic models impossible, and the inaccuracy in adsorbate-metal interactions described by the cluster model. By means of this method, the relative experimental Raman intensity peaks of ethylene adsorbed on metal surfaces were successfully reproduced. Moreover, the model analysis allowed relating the enhancement of the Raman intensity of both CO and ethylene upon chemisorption on the metal surface to both the gain of charges on C atoms and the polarization of orbitals. As such, the proposed method provides an accurate and efficient way to simulate and interpret Raman spectra of adsorbates on metal surfaces.