Time-dependent density functional methods for surface enhanced Raman scattering (SERS) studies

This paper describes the development and use of time-dependent density functional theory (TDDFT) methods for determining surface enhanced Raman scattering (SERS) spectra, with emphasis on pyridine interacting with a 20 atom silver cluster as a model of a molecule/nanoparticle system of interest to SERS. The calculations use a new implementation of a TDDFT linear response module in a locally modified version of NWChem for the TDDFT calculations. This code enables us to explore the influence of basis set effects and different choices of density functionals on the Raman spectra, including studies of correlation-consistent basis sets, and of hybrid density functionals. Previous work had employed the BP non-hybrid GGA functional, which works already quite well. Hybrid-GGA functionals such as B3LYP are better at reproducing the experimental spectra of the pyridine silver complex. However for relatively inexpensive calculations, the combination of BP with the DZVP basis set is able to provide semi-quantitative accuracy at reasonable cost, especially in conjunction with an appropriate pseudopotential for the silver atom.