Fast and accurate simulation of Raman spectra of gold-organic systems

Resolving the spectral Raman signature of molecules grafted onto a metallic support is often a difficult task, in which quantum chemistry methods allow for valuable additional rationalization and signal attributions, especially to probe the formation of a bond with the support. In the specific case of gold-organic architectures based on a Au-C bond, only a limited amount of experimental and theoretical reference data is available in the literature, and Raman simulations based on quantum mechanics quickly become unaffordable with the size of the system. In this work, we evaluate the precision of a cost-efficient DFTB method to simulate Raman spectra of gold-organic systems at different scales, from gold complexes to functionalized gold surfaces. After a validation of the method through a careful comparison of DFTB Raman spectra of organometallic gold(I) and (III) complexes to DFT and experimental reference data, we discuss the case of molecules grafted onto gold aggregates. For these simulations, the choice of the model (cluster or periodic surface) appears to be critical, and significant differences arise (positions and intensities of the peaks) when considering a full metallic slab, as allowed by the low computational cost of the method.