Fragment Embedding for Photochemical Electronic Structure Simulations

麻省理工学院的特洛伊·范·沃里斯教授获得了化学系化学理论、模型和计算方法计划颁发的奖项。在微观层面上，化学反应决定了发光二极管(LED)、太阳能电池和电池的寿命。最近，使用计算机模拟来预测有用的寿命已经成为可能--甚至是例行公事。这些模拟通过提供对可能难以直接测量的特性的洞察来补充实验。这个项目考虑使用嵌入计算机的方法，使其能够以比以往更高的精度模拟更大的系统。嵌入的基本思想包括将一个大系统分解成许多小的、重叠的片段，然后可以将这些片段缝合在一起来描述整个系统。Van Voorhim团队使用这些嵌入工具来研究与新兴的有机发光设备(OLED)和太阳能电池技术相关的分子的光化学。范·沃里斯教授是MIT Access的部门协调员，这是一个由化学、化学工程和材料科学联合开展的项目，旨在邀请一群未被充分代表的少数族裔本科生在学年的一个周末访问MIT。主要目的是鼓励学生考虑读化学研究生院。范·沃里斯教授还授权和装备他所在团队的研究生，向K-12学生介绍科学的美丽和力量。参与这一奖项的研究生和本科生被鼓励参加在当地学校表演的麻省理工学院化学“魔术秀”；培训研究生向K-12学生交流科学概念的研究交流实验室；麻省理工学院化学“一天科学家”中学夏令营的女科学家；以及麻省理工学院博物馆针对儿童和家庭的“周六科学”计划。范沃里斯小组正在开发具有变革性的电子结构方法，其中碎片是基本的构建块。我们的目标是创造出比最先进的近似方法更快、更准确的新工具，促进以前无法获得的化学模拟。作为起点，他们发展了一系列基于Bootstrap嵌入方法的片段嵌入理论。关键的实现是波函数嵌入允许以一种稳健的方式组合重叠的轨道碎片。由此产生的理论绕过了大多数波函数理论固有的比例挑战，只需要对非常小的碎片进行计算，这些碎片最终结合在一起就可以得到整个系统的图景。改进是通过使用多对扩展(MPE)对这些嵌入方法进行动态相关来完成的。最后，使用一种新的策略将这些技术扩展到激发态，该策略将这些状态识别为能量方差的局部最小值。作为这些工具的标志性应用，Van Voorhim团队研究了与新兴OLED和太阳能电池技术相关的分子中三重激子的能量学和动力学。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。

Professor Troy Van Voorhis of Massachusetts Institute of Technology is supported by an award from the Chemical Theory, Models and Computational Methods Program in the Division of Chemistry. At a microscopic level, chemical reactions determine how long light emitting diodes (LEDs), solar cells, and batteries will last. Recently it has become possible - and even routine - to make predictions about useful lifetimes using computer simulations. These simulations complement experiments by providing insight into properties that might difficult to measure directly. This project considers the use of embedding computer methods that may make it possible to simulate much larger systems with much higher accuracy than ever before. The fundamental idea of embedding involves breaking a large system up into many small, overlapping fragments that can then be stitched back together to describe the whole. The Van Voorhis group uses these embedding tools to study the photochemistry of molecules relevant to emerging organic light emitting device (OLED) and solar cell technologies. Professor Van Voorhis is the departmental coordinator of MIT ACCESS - a joint program between Chemistry, Chemical Engineering and Materials Science that invites a select group of underrepresented minority undergraduate students to visit MIT for a weekend during the academic year. The primary aim is to encourage the students to consider graduate school in chemistry. Professor Van Voorhis also empowers and equips graduate students within his group to introduce K-12 students to the beauty and power of science. Graduate and undergraduate students involved in this award are encouraged to participate in the MIT chemistry "Magic Show" that performs at local schools; the Research Communication Laboratory that trains graduate students to communicate scientific concepts to K-12 students; MIT Women in Chemistry's "Scientist for a Day" middle school camp; and the MIT museum's "Science on Saturdays" program that targets children and families. The Van Voorhis group is developing transformative electronic structure methods in which fragments are the fundamental building blocks. The goal is to create new tools that are both faster and more accurate than state-of-the-art approximations, facilitating chemical simulations that were previously inaccessible. As a starting point, they develop a family of fragment embedding theories based on the Bootstrap Embedding method. The key realization is that wave function embedding allows one to combine overlapping orbital fragments in a robust way. The resulting theory circumvents the scaling challenges inherent in most wave function theories by only requiring calculations on very small fragments, which are ultimately combined to obtain a picture of the entire system. Improvements are accomplished by dressing these embedding methods with dynamic correlation using the many pair expansion (MPE). Finally, these techniques are extended to excited states using a novel strategy that identifies such states as local minima of the energy variance. As a signature application of these tools, the Van Voorhis Group studies the energetics and dynamics of triplet excitons in molecules relevant to emerging OLED and solar cell technologies.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.