Electronic and vibronic interactions at weakly bound organic interfaces:: The case of pentacene on graphite

The electronic and vibronic processes at the interface between a pentacene monolayer and a graphite surface were characterized using a combination of density-functional theory (DFT) and dynamic vibronic coupling simulations. The electronic interactions were evaluated at the DFT level first between the highest occupied states of pentacene and the graphite surface, as well as among the pentacene molecules within a monolayer. The former are found to be ca. four times stronger than the latter for a parallel molecule/surface geometry. A dynamic vibronic model was used to analyze the interplay between the electronic and electron-vibration couplings and their effects on spectroscopic characteristics. The agreement between the simulated and experimental photoelectron spectra underlines the importance of weak electronic interactions on the vibronic coupling at the interface.