Molecules at Conducting Surfaces from First-Principles: Dark States and Distance-Dependent Broadening

Subsystem Density Functional Theory (DFT) can be taken to the time domain enabling first-principles simulations of electron dynamics of complex systems. Upon inspection, we observe all the relevant regimes proper of non-Markovian open quantum system dynamics: electronic energy transfer and screening. Contrary to interactions between molecular systems, when molecules interact with conducting surfaces the electron dynamics is strongly non-Markovian with dramatic repercussions to the molecule’s response to external perturbations. Metals and semiconductors typically have large polarizabilities, and even in a regime of low coupling their effect on molecular species is significant: line broadening, peak shift, and intensity borrowing are observed and explained in terms of inter-subsystem dynamical interactions and a many-body decomposition of the system’s response function in a way that transcends Fermi Golden Rule. We characterize the decay of an energy level's broadening with molecule-surface distance, and inspect bright as well as dark states.