Full embedding QM/MM scheme for modeling excited state proton transfer processes

普渡大学的柳德米拉·V·斯利普琴科(Lyudmila V.Slipchenko)得到了化学系化学理论、模型和计算方法项目的一项奖励，该奖项旨在开发新的计算和理论工具，用于描述涉及电子的分子的质子转移，这些分子中的电子通常是通过吸收光来激发的。要研究的系统处于溶液中或其他复杂环境中。被称为激发态质子转移(ESPT)的现象是普遍存在的。它自然存在于在生物学中扮演许多重要角色的光活性蛋白质中，并且发生在DNA链之间，作为一种消散多余紫外线辐射的途径。在技术上，ESPT被用于人造光设备、荧光化学传感器，以及用光脉冲控制局部环境的酸度。然而，对ESPT途径的机械理解对于设计高效的光化学电池或光酸来说是必不可少的，仍然是不完整的。这项研究有望通过阐明环境(溶剂、电解质、蛋白质基质)在这些事件中的作用，有助于理解和最终控制ESPT过程。这一知识将有助于科学家和工程师设计新型的光酸、化学传感器和人造光设备。在这个项目中开发和验证的算法将广泛分布，并为化学、生物和材料中的各种光诱导过程的预测性研究服务。Slipchenko和她的研究小组旨在通过以下方式表征静态和动态环境对复杂的光化学和光物理过程的影响：(I)开发基于QM/MM(量子力学/分子力学)类型的新的基于第一原理的方法；(Ii)通过创建浓缩相光化学数据库来验证和比较该方法相对于其他已建立的和新兴的方法；以及(Iii)应用新开发的工具来研究溶剂化光酸和蛋白质中的ESPT机制，如GFP和PYP。所提出的方法是基于电子激发态的可极化量子力学/分子力学(QM/MM)方法，其中环境(MM部分)用复杂的有效碎片势(EFP)方法描述。这项工作通过以下几个方面提高了QM/EFP方法的精确度和适用性：(I)建立了一个完全嵌入的QM/EFP模型，其中量子和经典系统之间的所有相互作用都是量子力学的；(Ii)将该模型推广到生物环境中；(Iii)发展了QM/EFP激发态分子动力学算法。该研究的创新之处在于建立了一种独特的全嵌入QM/MM模型，并将其应用于各种复杂环境下的激发态动力学。拟议的研究通过将新的计算机代码整合到开源、可免费获得的libefp库和开源PSI4、GAMESS和NWChem电子结构包中，并作为Q-Chem和MOLCAS量子化学软件的开源模块，为研究基础设施做出了贡献。拟议的浓缩相光化学数据库载有不同环境中的各种光活性分子，将通过为扩展系统提供新开发和建立的方法的基准和提供在线教程，为社区的量子化学教育作出贡献。

Lyudmila V. Slipchenko of Purdue University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Chemistry Division to develop new computational and theoretical tools for describing the transfer of protons involving molecules in which the electrons have been excited, often by absorption of light. The systems to be studied are in solution or in other complex environments. The phenomenon known as excited state proton transfer (ESPT) is ubiquitous. It naturally occurs in photoactive proteins, which play many important roles in biology, and takes place between DNA strands as a pathway for dissipating excess UV radiation. In technology, ESPT is exploited in artificial photo-devices, fluorescent chemo-sensors, and for manipulating the acidity of local environment with light pulses. However, mechanistic understanding of ESPT pathways, which is essential for design of efficient photochemical cells or photoacids, remains incomplete. This research is expected to contribute to the understanding and eventual control of ESPT processes by elucidating the role of environment (solvent, electrolyte, protein matrix) in these events. This knowledge will benefit scientists and engineers designing new classes of photoacids, chemo-sensors and artificial photo-devices. The algorithms developed and validated in this project will be broadly distributed and serve for predictive studies of a variety of photo-induced processes in chemistry, biology, and materials. Slipchenko and her research group aim to characterize static and dynamic environment effects on complex photochemical and photophysical processes such as ESPT by (i) developing novel first-principles based methodology of QM/MM (Quantum Mechanics/Molecular Mechanics) type, (ii) validating and benchmarking this methodology relative to other established and emerging methods by creating a condensed-phase photochemistry database, and (iii) applying newly developed tools for investigating ESPT mechanisms in solvated photoacids and proteins such as GFP and PYP. The proposed method developments are based on polarizable quantum mechanics/molecular mechanics (QM/MM) approach for electronic excited states, in which the environment (the MM part) is described by the sophisticated Effective Fragment Potential (EFP) method. The proposed work enhances the accuracy and applicability of the QM/EFP methods by (i) developing a full embedding QM/EFP model in which all interactions between the quantum and classical systems are accounted for quantum-mechanically, (ii) extending this model to biological environments, and (iii) developing QM/EFP excited state molecular dynamics algorithms. The novelty of the proposed research is in creating a unique full embedding QM/MM model and applying it to excited state dynamics in various complex environments. The proposed research contributes to the research infrastructure byintegrating new computer codes in the open-source, freely available libefp library and in open-source PSI4, GAMESS and NWChem electronic structure packages and as open-source modules in Q-Chem and MOLCAS quantum chemistry software. The proposed condensed-phase photochemistry database, containing a variety of photoactive molecules in various environments, will contribute to quantum chemistry education in the community by providing benchmarks of newly developed and established methods for extended systems and by supplying online tutorials.