Orbital Renormalization Effects on the Coupling between Molecular Excitations and Plasmons

Accurately describing the electronic structure of molecules on metal nanostructures is key to modeling their surface-enhanced properties. Particularly difficult is the modeling of the coupling between molecular excited states and plasmons. Here we present a computational efficient approach to study the renormalization effects on the molecular electronic structure and its optical properties due to the interactions with the metal surface. Accurate simulations of the renormalization effects are achieved by employing a hybrid atomistic electrodynamics and time-dependent density functional model. The coupling between the molecular absorption and the plasmon excitation depends strongly on the spectral overlap. Here we show that the renormalization effect for the benzene-tetracyanoethylene donor-acceptor complex interacting with a metal nanoparticle causes a 0.6 eV shift in the absorption band. Furthermore, we show that the coupling between the molecular absorption and the plasmon excitation is caused by interference between the molecular absorption, the image field of the metal nanoparticle, and the near field due to the plasmon excitation. The results presented here illustrate the importance of using first-principles simulations to understand in detail the coupling between molecular absorption and plasmon excitation.