Diabatic Representations:New Tools, New Uses and their Application to the Study of Nonadiabatic Processes Influenced by Conical Intersections

约翰霍普金斯大学的David Yarkony获得了化学系化学理论、模型和计算方法项目的奖励，他开发了新的理论工具来研究分子电子被激光、太阳或其他来源的光能激发后产生的化学反应。利用光能进行化学反应，如太阳能转换、光合作用、视觉，甚至人类DNA抗紫外线辐射的稳定性，都涉及到科学家所说的电子非绝热过程，简称非绝热过程。这样的过程涉及到代表不同电子状态的两个不同势能面的交集。它们本质上是量子力学的。虽然现有的计算工具允许描述较小的化学系统的非绝热过程，但用高度精确的理论方法处理更大、更复杂系统的方法仍然缺乏。Yarkony和他的同事正在实施一些技术，旨在将准确描述的范围扩展到更大、更复杂的系统。这些技术及其产品对科学界是免费提供的。也许最终比这些直接的好处更重要的是，这项提议的工作有可能改变化学物理学家对非绝热性的看法和计算其影响的方式。Yarkony利用近40年前提出的一个具有开创性的概念，对非绝热性的数学描述进行了重新表述，这个概念在科学上很贴切，但在其他方面却很神秘，被称为分子Aharonov Bohm效应。这些导致光稳定性的非绝热动力学的更精确的研究影响了理解社会相关过程的更广泛的社会目标，例如DNA如何保护自己免受辐射损伤。该项目有三个目标：(a)开发一种普遍适用的程序，将几何相纳入控制绝热动力学的单态哈密顿量，从而确定分子Aharonov Bohm效应的普遍性和大小，归因于能量不可达的锥形相交的几何相对单态核动力学的影响；(b)从现有的算法和新工具中构建一个通用程序，用于确定多状态系统的非绝热表示，该系统以一般方式将基于非绝热的属性纳入一个框架内，该框架明确包含衍生耦合和伪（也称为恶魔）奇点的测试，这些奇点可以使基于属性的非绝热无效；(c)使用现有代码和(b)中开发的程序，从精确的电子结构数据构建耦合的非绝热状态表示，以描述生物相关系统中的解离光化学，包括苯胺和咪唑。免费提供的程序和高质量的绝热哈密顿量使化学物理学家能够使用这些成果来设计研究工作，从而在非绝热化学方面取得进一步进展。github域提供了对发布的非绝热表示的免费访问。

David Yarkony of Johns Hopkins University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry to develop new theoretical tools to study chemistry that arises after a molecule's electrons are excited by light energy from a laser, the sun or another source. The use of light energy to do chemistry in solar energy conversion, photosynthesis, vision and even the stability of human DNA against ultraviolet radiation all involve what scientists call electronically nonadiabatic processes, nonadiabaticity for short. Such processes involve the intersection of two different potential energy surfaces representing different electronic states. They are essentially quantum mechanical. While existing computational tools allow the description of nonadiabatic processes for smaller chemical systems, methods for treating larger, more complex systems with highly accurate theoretical approaches are still lacking. Yarkony and his coworkers are implementing techniques designed to extend the range of accurate descriptions to larger, more complex systems. These techniques and their products, are freely available to the scientific community. Perhaps ultimately even more significant than these immediate benefits, the proposed work has the potential to transform the way chemical physicists think about nonadiabaticity and compute its effects. Yarkony has introduced a reformulation of the mathematical description of nonadiabaticity by exploiting a seminal notion introduced almost 40 years ago, with the scientifically apt, but otherwise arcane appellation, the Molecular Aharonov Bohm effect. These more precise studies of nonadiabatic dynamics leading to photo-stability impact the broader societal goal of understanding societally relevant processes, such as how DNA protects itself against radiation damage. The project has three goals: (a) to develop a generally applicable procedure to incorporate the geometric phase into the single state Hamiltonian governing adiabatic dynamics enabling determination of the prevalence and magnitude of the Molecular Aharonov Bohm effect, the effect of the geometric phase attributable to energetically inaccessible conical intersections on single state nuclear dynamics; (b) to construct from an existing algorithm and new tools, a general program for determining diabatic representations for multi-state systems which incorporates in a general manner properties based diabatizations within a framework which explicitly incorporates derivative couplings and tests for spurious (also termed diabolical) singularities that can invalidate the property based diabatizations; and (c) to use existing code and the program developed in (b) to construct coupled diabatic state representations from accurate electronic structure data to describe dissociative photochemistry in bio-related systems, including initially aniline and imidazole. . The freely available programs and high quality diabatic Hamiltonians enable chemical physicists to use these deliverables to design research efforts to make further progress in nonadiabatic chemistry. A github domain provides free access to the published diabatic representations.