Interpretation of Vibrational Spectra in Electrochemical Environments from First-Principle Calculations: Computational Strategies

Abstract

The vibrational frequencies of carbonate adsorbed on Pt (111) electrodes have been investigated by the cluster-model approach within the hybrid B3LYP DFT-based method. A rather large cluster model was used to represent the Pt (111) surface and a fast and efficient procedure based on the normal coordinate approach is proposed to compute the vibrational frequencies of adsorbed carbonate. This normal coordinate approach avoids the expensive computation of the hessian matrix of the cluster plus adsorbate supersystem. In addition, the vibrational analysis has also been carried out for carbonate in mono- and bi-dentate complexes that are often used as reference to assign the vibrational spectra of adsorbed carbonate. First, it is shown that for the mono- and bi-dentate complexes the B3LYP frequencies are comparable to the experimental data. The comparison to computed vibrational frequencies for adsorbed carbonate does not support the Surface vs Organometallic Chemistry analogy usually invoked to assign the infrared bands of adsorbed species. Finally, to better represent the electrochemical environment, the effect of a uniform external electric field on the adsorbed carbonate frequencies has been analysed.