The Development of Spin-Adiabatic Approaches for Studying Spin-Crossing Reactions

在化学系化学理论、模型和计算方法(CTMC)计划和刺激竞争研究(EPSCoR)计划的支持下，俄克拉荷马大学的邵一汉和杨志波将开发用于研究自旋交叉反应的自旋绝热方法。自旋交叉反应是一系列化学、生化和光化学过程的核心，如气相离子-分子反应、过渡金属络合物催化、氧活化、天然和人工分解水以及化学发光/生物发光。然而，由于以下几个原因，模拟自旋交叉反应仍然具有极大的挑战性：这类反应的性质复杂；难以同时探索多个自旋-非绝热势能面；缺乏足够的方法/软件支持来有效地识别自旋交叉反应能量途径(和反应自由能途径)并准确预测其反应速率。为了克服这一挑战，邵和杨小组将开发一种准确、高效和开源的计算协议，直接在最低能量的自旋-绝热势能面上研究自旋交叉反应。在该计划下开发的软件将以免费和开源的方式发布。根据这一奖项，该团队还建立了一个QM-MM.org网站，并每月举办网络研讨会，为年轻研究人员提供机会学习计算化学工具的最新应用。俄克拉荷马大学的Shao博士、杨博士和他们的研究团队正在开发构建和探索自旋绝热表面的方法，以便在过渡态搜索或分子动力学模拟过程中，人们可以自动、平稳地从高自旋状态转换到低自旋状态(反之亦然)。这项研究预计将以下列目标进行：(A)实施多个自旋-轨道耦合和自旋交叉概率方案；(B)形成分析能量梯度；(C)通过混合量子力学分子力学模型纳入环境影响；(D)在自由能计算中结合路径优化方法；(E)在选定的组态上改进活动空间或耦合团簇量子化学计算的能量和自由能结果；以及(F)评估更高能量的自旋非绝热激发态的贡献。该团队将把这些新的计算方法应用于通过质谱学实验研究的几个自旋交叉离子-分子反应。他们还将研究化学发光和生物发光中的氧合反应，以获得机理上的见解。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

WIth support from the Chemical Theory, Models and Computational Methods (CTMC) program in the Division of Chemistry and the Established Program to Stimulate Competitive Research (EPSCoR), Yihan Shao and Zhibo Yang of the University of Oklahoma will develop spin-adiabatic approaches for studying spin-crossing reactions. Spin-crossing reactions are central to a wide range of chemical, biochemical, and photochemical processes such as gas-phase ion-molecule reactions, transition metal complex catalysis, oxygen activation, natural and artificial water splitting, and chemiluminescence/bioluminescence. However, it remains extremely challenging to model spin-crossing reactions due to several reasons: complex nature of such type of reactions; difficulties of simultaneously exploring multiple spin-diabatic potential energy surfaces; lack of sufficient methodology/software support for efficiently identifying spin-crossing reaction energy pathway (and reaction free energy pathway) and for accurately predicting their reaction rates. To overcome this challenge, the Shao and Yang groups will develop an accurate, efficient, and open-source computational protocol for studying spin-crossing reactions directly on the lowest-energy spin-adiabatic potential energy surface. Software developed under this program will be released in a free and open-source manner. Under this award, the team also host a qm-mm.org website and hold monthly webinars to provide young researchers an opportunity to learn from the latest applications of computational chemistry tools. Dr. Shao, Dr. Yang and their research teams at the University of Oklahoma are developing methods to construct and explore spin-adiabatic surfaces, so that one can transition automatically and smoothly from a high-spin state to a lower-spin one (or vice versa) during a transition state search or molecular dynamics simulation. This research is projected to proceed with the following objectives: (a) implementation of multiple spin-orbit coupling and spin- crossing probability schemes; (b) formulation of analytical energy gradients; (c) incorporation of environment effects through hybrid quantum mechanical molecular mechanical models; (d) combination with pathway optimization methods in free energy calculations; (e) improvement to the energy and free energy results with active-space or coupled-cluster quantum chemistry calculations on selected configurations; and (f) assessment of the contribution from higher-energy spin-diabatic excited states. The team will apply these new computational methods to several spin-crossing ion-molecule reactions studied with mass spectrometry experiments. They will also investigate oxygenation reactions in chemiluminescence and bioluminescence to gain mechanistic insights.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.