Light Absorption of Contacted Molecules: Insights and Impediments from Atomistic Simulations

Abstract : The absorption spectrum of a prototypical organic molecule (hydroquinone) in contact with semi-infinite metallic nanowires is investigated by means of atomistic parameter-free simulations. We employ an open boundary Liouville-van Neumann approach in conjunction with approximate time-dependent density functional theory to reveal changes in absorbance with respect to the gas phase spectrum. It is found that molecule–metal hybridization leads to state specific shifts in the band maxima and significant broadening. In addition, the line shape acquires a nonsymmetrical Fano character for strong molecule–metal coupling. As the strong plasmonic response of the metal leads overshadows molecular excitations, we show that construction of a differential cross section for the junction with and without embedded molecule effectively uncovers hidden spectral features.