EAGER: Quantum Transition State Theory for Electronically Nonadiabatic Processes

化学部的化学理论、模型和计算方法项目正在支持康奈尔大学的Nandini Ananth教授开发描述过程的模型，其中量子力学对于理解复杂化学和物理系统的动力学非常重要。通过了解亚原子水平上的相互作用和量化反应速率来描述化学过程是我们理解化学、物理和生物学的核心。经典过渡态理论（TST）的引入彻底改变了我们对化学反应的理解，因为它允许对大型系统的反应速率进行有效的计算，而在这些系统中，不可能进行精确、详细的量子力学计算。尽管这个理论取得了许多成功，但它不能正确地描述量子力学行为起重要作用的过程。最近，一个量子TST （QTST）被推导出来，它将量子效应融入到类似经典TST的形式中。在这项工作中，Ananth和她的同事们正在努力将QTST扩展到一个根本重要的反应类别，目前它不适用-电子和能量转移过程。发展这样一个理论可以为复杂的光诱导化学反应的机制提供前所未有的见解。在将QTST扩展到电子和能量转移过程中，必须面对两个重大的技术挑战。首先，量子系统的离散电子态必须用连续的经典变量代替，这是TST公式所必需的。其次，由电子态跃迁和核运动之间的耦合引起的非绝热效应必须精确地描述。Ananth采用基于Schwinger角动量理论的映射协议将离散状态映射到笛卡尔相空间变量，并使用量子力学的路径积分表示将非绝热效应纳入实时通量侧相关函数的精确经典同构表达式。将得到所需的TST表达式作为通量侧相关函数的短时极限。这种非绝热QTST将是通用的，并可用于提供对任何非绝热量子力学化学过程的反应速率和反应途径的良好估计。此外，研究小组的目标是建立一个严格的近似推导，基于路径积分的动力学，从复杂化学系统的实时模拟中提供定量的反应速率和详细的机制信息。

With this EAGER award, the Chemical Theory, Models and Computational Methods Program in the Chemistry Division is supporting Professor Nandini Ananth at Cornell University to develop models that describe processes where quantum mechanics is important for understanding the dynamics of complex chemical and physical systems. Characterizing chemical processes by understanding interactions at a sub-atomic level and by quantifying reaction rates is central to our understanding of chemistry, physics and biology. The introduction of classical transition state theory (TST) revolutionized our understanding of chemical reactions, because it allowed the efficient calculation of reaction rates for large systems in which it is not possible to do exact, detailed quantum mechanical calculations. Despite its many successes this theory cannot correctly describe processes where quantum mechanical behavior plays an important role. Recently, a quantum TST (QTST) was derived that incorporates quantum effects into formalism that resemble classical TST. In this work, Ananth and her coworkers are working to extend the QTST to a fundamentally important class of reactions for which it is currently inapplicable - electron and energy transfer processes. Developing such a theory could provide unprecedented insights into the mechanism of complex photo-induced chemical reactions.There are two significant technical challenges that must be met in extending QTST to electron and energy transfer processes. First, the discrete electronic states of the quantum system must be replaced with continuous, classical variables that are necessary for the TST formulation. Second, nonadiabatic effects arising from coupling between electronic state transitions and nuclear motions must be accurately described. Ananth employs a mapping protocol based on Schwinger's angular momentum theory to map discrete states to Cartesian phase-space variables and uses the path-integral representation of quantum mechanics to incorporate nonadiabatic effects into an exact, classically isomorphic expression for a real-time, flux-side correlation function. The desired TST expression will be obtained as the short-time limit of the flux-side correlation function. This nonadiabatic QTST will be general, and can be used to provide a good estimate of reaction rates and insights into reaction pathways for any nonadiabatic, quantum mechanical chemical process. Further, the research team aims to establish a rigorous derivation of an approximate, path-integral based dynamics to provide quantitate reaction rates and detailed mechanistic information from real-time simulations of complex chemical systems.