Excited State Specific Correlation Methods in Quantum Chemistry

在化学系化学理论、模型和计算方法计划的支持下，加州大学伯克利分校的Eric Neuscamman正在为光驱动化学的计算机模拟开发新的工具。无论是研究阳光对DNA的损伤，还是模拟光合作用的工业过程，理解光驱动化学变化的机制都很困难，因为这种作用发生的规模很小，速度很快。现代实验技术可以提供正在发生的事情的一瞥，但往往没有回答关键问题，例如分子在从阳光中吸收能量后自我转化的完整系列形状。Neuscamman小组将开发和部署新一代计算机模型，在当前方法有限的高度优先的化学领域忠实地模拟这些过程。特别是，将电子从分子的一侧移动到另一侧或同时移动多个电子的光驱动过程，除了在最小的分子中外，目前的工具无法准确模拟，而这些过程的关键应用发生在涉及数百个原子的技术和生物环境中。通过弥合这一差距，Neuscamman小组旨在加深我们对光驱动化学以及依赖它的关键技术的理解。在这项研究的同时，Neuscamman小组将把其扩展工作扩展到中学生，教授数学优化方法的基本原理，这些方法支持从化学到机器学习的科学优先事项。这种基于游戏的推广还将围绕斜率和曲率等概念播下种子，这样当学生最终发现自己在微积分课堂上时，他们已经熟悉了微积分在现实世界中令人兴奋和有利可图的用途。通过邀请本科生作为此次外展的导师，该活动将拓宽中学生的视野，并加强对活跃的本科生同事参与者的理解。了解分子吸收光的跃迁能量是化学的核心。虽然几十年来的理论工作一直致力于预测电子(如HOMO、→、LUMO)激发的跃迁能，但现有的理论方法仍然不能很好地适用于某些类别的电子激发。其中两个例子是电荷转移态，它是生物和人工光捕获以及许多酶反应机制的中心，以及双重激发，它在颜料和生色团的扩展π共轭网络以及许多过渡金属络合物中很常见。Neuscamman小组将在电子激发态平均场处理的最新突破的基础上，构建一套预计将是高精度和负担得起的耦合团簇和相关方法，用于模拟大分子和分子组件中的电子激发态。这些方法有可能显著提高模拟电荷转移和双激发态的最先进水平，对化学、生物学、材料和系统化学具有潜在的长期科学影响。该奖项反映了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 program in the Division of Chemistry, Eric Neuscamman of the University of California at Berkeley is developing new tools for the computer simulation of light-driven chemistry. Whether studying DNA damage from sunlight or industrial processes that mimic photosynthesis, understanding the mechanisms by which light drives chemical change is made difficult by the tiny scales and fast pace at which the action occurs. Modern experimental techniques can offer glimpses of what is going on, but often leave key questions unanswered, such as the full series of shapes a molecule transforms itself through after absorbing energy from sunlight. The Neuscamman group will develop and deploy a new generation of computer models that faithfully simulate these processes in high priority areas of chemistry where current methods are limited. In particular, light-driven processes that move electrons from one side of a molecule to the other or that move multiple electrons at once cannot be simulated accurately by current tools except in the smallest molecules, whereas key applications of these processes occur in technological and biological settings involving hundreds of atoms. By bridging this gap, the Neuscamman group aims to deepen our understanding of light-driven chemistry and the crucial technologies that rely on it. In tandem with this research, the Neuscamman group will expand its outreach work to middle school students, teaching the underlying principles of mathematical optimization methods that support scientific priorities from chemistry to machine learning. This game-based outreach will also plant seeds around concepts like slope and curvature so that students are already familiar with exciting and lucrative real-world uses for calculus when they eventually find themselves in a calculus classroom. By engaging undergraduate students as instructors in this outreach, the activity will both broaden middle school student horizons and reinforce understanding for the active undergraduate co-worker participants. Understanding the energies of transitions in which molecules absorb light is central to chemistry. While decades of theoretical work have been dedicated to predicting the transition energies of electronic (e.g. HOMO→LUMO) excitations in particular, some categories of electronic excitation are still poorly served by available theoretical methods. Two examples of these are charge transfer states, which are central to biological and artificial light harvesting as well as many enzymatic reaction mechanisms, and double excitations, which are common in the extended π-conjugation networks of pigments and chromophores as well as in many transition metal complexes. The Neuscamman group will build on recent breakthroughs in the mean-field treatment of electronically excited states to construct what is anticipated to be a highly accurate, and affordable suite of coupled cluster and related methods for modeling electronically excited states in large molecules and molecular assemblies. These methods have the potential to significantly improve the state-of-the art in modeling both charge transfer and doubly excited states with potential broad long term scientific impacts for chemistry, biology, materials and systems chemistry.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.