Theoretical studies of bond rupture and stability of molecular junctions

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Current-induced rupture of chemical bonds is a major concern when single molecules are being considered as electronic components in nano-scale devices. The most widely studied architecture in this context is a molecular junction, where a single molecule is bound to metal or semiconductor electrodes. Molecular junctions represent a unique architecture to investigate molecules in a distinct nonequilibrium situation and, in a broader context, to study basic mechanisms of charge and energy transport in a many-body quantum system at the nanoscale. The objective of this project is to investigate current-induced bond rupture processes in molecular junctions, caused by coupling of the transport electrons to the vibrations of the molecule, and their implications for the stability of the junctions. To this end, the theory and methodology of vibrationally-coupled electron transport in molecular junctions will be extended to incorporate dissociative nuclear potentials. Specifically, the hierarchical quantum master equation method will be adapted for this purpose, which provides a very accurate, in principle numerically exact framework to study charge transport in molecular junctions at a fully quantum mechanical level including nonperturbative and non-Markovian effects. The extended methodology will be used to investigate the fundamental mechanisms of current-induced bond rupture in molecular junctions considering models ranging from the adiabatic to the nonadiabatic transport regime, including nonresonant and resonant transport scenarios as well as destructive and nondestructive dissociation. The methodology, to be developed in this project, will provide important benchmarks to validate more approximate methods and can also build a basis towards future applications to study current-catalyzed chemical reactions.