Charge transport through molecular junctions is often described either as a purely coherent or a purely classical phenomenon, and described using the Landauer–Büttiker formalism or Marcus theory (MT), respectively. Using a generalised quantum master equation, we here derive an expression for current through a molecular junction modelled as a single electronic level coupled with a collection of thermalised vibrational modes. We demonstrate that the aforementioned theoretical approaches can be viewed as two limiting cases of this more general expression and present a series of approximations of this result valid at higher temperatures. We find that MT is often insufficient in describing the molecular charge transport characteristics and gives rise to a number of artefacts, especially at lower temperatures. Alternative expressions, retaining its mathematical simplicity, but rectifying those shortcomings, are suggested. In particular, we show how lifetime broadening can be consistently incorporated into MT, and we derive a low-temperature correction to the semi-classical Marcus hopping rates. Our results are applied to examples building on phenomenological as well as microscopically motivated electron-vibrational coupling. We expect them to be particularly useful in experimental studies of charge transport through single-molecule junctions as well as self-assembled monolayers.

中文翻译：

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超越分子连接中的Marcus理论和Landauer-Büttiker方法：统一框架

通过分子连接的电荷传输通常被描述为纯连贯现象或纯经典现象，并分别使用Landauer-Büttiker形式主义或Marcus理论（MT）进行描述。使用广义量子主方程，我们在这里导出通过分子结的电流表达式，该分子结被建模为单个电子能级并结合了热化振动模式。我们证明了上述理论方法可以看作是这种更一般表达的两个极限情况，并给出了在较高温度下有效的一系列近似结果。我们发现MT通常不足以描述分子的电荷传输特性，并且会引起许多伪像，尤其是在较低温度下。替代表达式 建议保留其数学上的简单性，但要纠正这些缺点。特别是，我们展示了如何将延长寿命的方法始终如一地纳入MT中，并对半经典的Marcus跳变率进行了低温校正。我们的结果被应用于基于现象学以及微观驱动的电子振动耦合的例子。我们希望它们在通过单分子结以及自组装单分子层进行电荷传输的实验研究中特别有用。我们的结果被应用于基于现象学以及微观驱动的电子振动耦合的例子。我们希望它们在通过单分子结以及自组装单分子层进行电荷传输的实验研究中特别有用。我们的结果被应用于基于现象学以及微观驱动的电子振动耦合的例子。我们希望它们在通过单分子结以及自组装单分子层进行电荷传输的实验研究中特别有用。