Simulating plasmon-enhanced spectroscopy from a hybrid quantum/classical approach

Plasmon-enhanced spectroscopies, such as surface enhanced Raman spectroscopy, permit the detection and characterization of few, or even single, molecules in proximity to a metal surface or nanoparticle. First-principles prediction of enhanced molecular excitations and their coupling with plasmons through a strong optical near-field, which may alter and broaden the molecular optical or vibrational spectra, may aid the rational optimization of substrates for specific analytes and experiments. We have implemented a hybrid quantum/classical scheme to compute molecular and electronic electrodynamics in the time-domain. Analyte molecules are treated on the quantum mechanical level with time-propagation time-dependent density functional theory while solute and metal structures are treated on the classical level with quasistatic finite-difference time-domain method. Examples of this method applied to sugar isomers in metal-lined optical cavities are presented.