Understanding effects of nuclear dynamics on single-molecule conductance

The pioneering theory of a molecular rectifier by Aviram and Ratner in 1974 and the experimental realization of a molecular junction by Reed in 1990 generated widespread enthusiasm for the potential of using molecules as components of electronic circuitry. To this end, research in molecular electronics over the past three decades has pursued the development of circuit components, such as resistors and diodes, as well as devices, such as switches and sensors, that harness the underlying quantum nature of nanoscale charge transport. In addition to practical motivations for developing molecular electronics, a single-molecule junction, i.e., a system consisting of a molecule bridged between two electrodes, is an excellent testbed for advancing our fundamental understanding of charge transport at the nanoscale. As nuclear motion can significantly affect conductance, accurate and physically meaningful dynamical models of single-molecule junctions can provide valuable insight into the relationships between chemical dynamics and conductance fluctuations. Here, we investigate which types of molecular and interfacial vibrations produce strong conductance fluctuations by combining a tunneling model of conductance with ab initio molecular dynamics simulations of single-molecule junctions. We apply our results to propose junctions with significantly lower conductance uncertainty. In addition, we study chemical reactions in molecular junctions. Our results show how the junction environment can substantially alter the kinetics of the reaction and perhaps produce a conductance signature of the transition state.