Understanding the distance dependence of the parameters underpinning Marcus theory is imperative when interpreting the results of experiments on electron transfer (ET). Unfortunately, most of these parameters are difficult or impossible to access directly with experiments, necessitating the use of computer simulations to model them. In this work, we use molecular dynamics simulations in conjunction with constrained density functional theory calculations to study the distance dependence of the electronic coupling matrix element, |H_RP|, for bimolecular ET. Contrary to what is typically assumed for such intermolecular reactions, we find that the magnitude of |H_RP| does not decay exponentially with the center-of-mass separation of the reactants, r_COM. The addition of other simple measures of donor/acceptor (D/A) orientation did not improve the correlation of |H_RP| with r_COM. Using the minimum distance separation, r_min, of the reactants as the structural descriptor allowed the system to be partitioned into high-coupling/close-contact and low-coupling/non-contact regimes, but large fluctuations of |H_RP| were still found for the close-contact reactant pairs. Despite the persistent large fluctuations of |H_RP|, its mean value was found to decay piecewise exponentially with increasing r_min, which was attributed to significant changes in the average D/A pair structure. The results herein advise one to use caution when interpreting the experimental results derived from spherical reactant models of bimolecular ET.

中文翻译：

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双分子电子转移的分子动力学模拟：距离相关的电子耦合

在解释电子转移 (ET) 实验结果时，了解支持 Marcus 理论的参数的距离依赖性是必不可少的。不幸的是，这些参数中的大多数很难或不可能通过实验直接访问，因此需要使用计算机模拟来对其进行建模。在这项工作中，我们使用分子动力学模拟结合约束密度泛函理论计算来研究电子耦合矩阵元素的距离依赖性，| H _RP |，用于双分子 ET。与这种分子间反应的典型假设相反，我们发现 | H _RP | 不随反应物的质心分离而呈指数衰减，r_通讯。添加其他简单的供体/受体 (D/A) 取向测量并没有改善 | 的相关性。H _RP | 与r _COM。使用反应物的最小距离间隔r _min作为结构描述符允许将系统划分为高耦合/紧密接触和低耦合/非接触状态，但 H _RP | 仍然发现紧密接触的反应物对。尽管持续大幅波动| H _RP |，发现其平均值随着r _{min 的}增加呈分段指数衰减，这归因于平均 D/A 对结构的显着变化。本文的结果建议人们在解释从双分子 ET 的球形反应物模型得出的实验结果时要谨慎。