Theoretical studies of bond rupture and stability of molecular junctions

当单分子被认为是纳米器件中的电子元件时，电流诱导的化学键断裂是一个主要问题。在这种背景下，研究最广泛的结构是分子结，其中单个分子结合到金属或半导体电极上。分子结代表着一种独特的体系结构，可以在不同的非平衡状态下研究分子，在更广泛的背景下，在纳米尺度上研究多体量子系统中电荷和能量传输的基本机制。这个项目的目的是研究分子结中电流诱导的键断裂过程，这是由传输电子与分子振动的耦合引起的，以及它们对结稳定性的影响。为此，分子结中振动耦合电子输运的理论和方法将扩展到包括解离核势。具体地说，分层量子主方程方法将被用于这一目的，它提供了一个非常准确的、原则上精确的数值框架，以在完全量子力学水平上研究分子结中的电荷输运，包括非微扰和非马尔可夫效应。扩展的方法将被用来研究分子结中电流诱导键断裂的基本机制，考虑从绝热到非绝热输运的各种模型，包括非共振和共振输运场景以及破坏性和非破坏性解离。将在本项目中开发的方法学将为验证更接近的方法提供重要的基准，并也可以为未来应用于研究电流催化化学反应奠定基础。

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.