CAREER: Stochastic Methods for Electronic Excitations in Complex Nanoscale System

对电子激励的定量理论理解对于寻找和设计新的电子器件是必要的。这些系统的性质是由延伸到纳米尺度的量子力学相互作用主导的。在这些情况下，电子激发的模拟对传统的理论方法提出了相当大的挑战，而且这种计算通常被认为是难以处理的。该职业奖支持三个重点领域：(i)开发打破当前计算限制的新方法；（ii）将先进的量子多体理论应用于复杂的纳米系统，阐明电子器件设计的新策略；（iii）在物理、化学和材料科学方面的教育活动，重点关注凝聚态系统的电子和光学性质。研究小组结合了新的数值技术来描述激发和电子-电子相互作用的动力学。该方法基于非确定性量子统计方法。它的计算成本不高，而且可以高精度地处理超大的系统。该项目还提供了一种新的方法来解释有限的温度效应。因此，在计算结果和实验观测之间建立直接对应关系是可能的。在这个项目中开发和使用的理论工具将提供给社区。这些新进展将应用于光伏系统，以阐明结构和化学修饰如何影响光伏器件及其界面中的电子激发。该项目的教育目标是为研究生、本科生以及K-12学生提供工具和培训。该项目将为研究生提供理论和计算方面的研究经验。通过与加州少数民族参与联盟合作的这项提案，将为本科生建立多个研究和培训机会。该奖项还支持一项关于分子和电子结构之间关系的新的教育K-12推广活动。本职业奖支持电子激发理论的研究和教育。研究小组将基于波函数和算子期望值的有效数值采样，开发多体微扰理论的随机形式。电子-电子相互作用的表示是在格林函数形式中推导出来的，其中包括高阶相关（顶点）项。这一步骤与计算电子-声子耦合的一种新的随机形式相结合，需要考虑与实验进行定量比较。研究小组将确定预测电子激发的多体摄动理论的最准确和有效的随机实现。这些新进展将应用于具有强电荷转移和激子效应的有机光伏系统。该项目将分三个步骤进行：(i)开发一个精确的随机多体框架，超出常用的近似，包括处理强电子-空穴相互作用（顶点项）；（ii）发展新的随机方法来研究大型系统中振动对激励能的影响；(3)新的随机框架在大分子系统及其凝聚相组装中的应用。新的计算框架将使模拟具有成百上千个原子的系统中的量子多体相互作用成为可能。结果将提供一个详细的了解如何组成，环境和分子间相互作用的程度影响有机（光电）电子系统的性质。本研究有效地连接了理论化学和凝聚态物理的研究领域。这种多方面的方法被整合到研究生和本科生培训中，以及新开发的K-12外展活动中。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NONTECHNICAL SUMMARYA quantitative theoretical understanding of electronic excitations is necessary for searching and designing new electronic devices. Properties of these systems are dominated by quantum mechanical interactions that extend over nanometer scales. In these cases, simulations of electronic excitations pose a considerable challenge for conventional theoretical approaches, and such calculations are often deemed untractable. This CAREER award supports three focus areas: (i) development of new methods that break the current computational limitations; (ii) application advanced quantum many-body theory to complex nanoscale systems to elucidate new strategies for design of electronic devices; and (iii) educational activities in physics, chemistry, and materials science focusing on electronic and optical properties in condensed systems.The research team combines new numerical techniques to describe the dynamics of excitations and electron-electron interactions. The methodology is based on a non-deterministic quantum-statistical approach. It is computationally inexpensive, and it allows treating exceedingly large systems with high accuracy. The project also provides a new methodology to account for finite temperature effects. Hence, it is possible to establish a direct correspondence between computational results and experimental observations. The theoretical tools developed and used in this project will be made available to the community. The new developments will be applied to photovoltaic systems to elucidate how structural and chemical modifications affect the electronic excitations in photovoltaic devices and their interfaces.The educational goals of the project aim to provide tools and training for graduate, undergraduate, as well as K-12 students. The PI will provide graduate students with research experience in theory and computation. Multiple research and training opportunities for undergraduate students will be established through this proposal in collaboration with the Califonia Alliance for Minority Participation. This award also supports a new educational K-12 outreach activity on relations between molecular and electronic structures. TECHNICAL SUMMARYThis CAREER award supports research and education in the theory of electronic excitations. The research team will develop a stochastic form of the many-body perturbation theory based on an efficient numerical sampling of wavefunctions and expectations values of operators. The representation of the electron-electron interactions is derived in the Green’s function formalism, which includes high order correlation (vertex) terms. This step is combined with a new stochastic formalism for computing electron-phonon couplings, which need to be considered for quantitative comparison with experiments. The research team will determine the most accurate and efficient stochastic implementations of the many-body perturbation theory for predicting electronic excitations. The new developments will be applied to organic photovoltaic systems with strong charge transfer and excitonic effects.This project will be carried out in three steps: (i) development of an accurate stochastic many-body framework beyond the commonly used approximations, including the treatment of strong electron-hole interactions (vertex terms); (ii) development of new stochastic methodology to study vibrational effects on excitation energies in large systems; and (iii) applications of the new stochastic framework to large molecular systems and their assemblies in the condensed phase. The new computational framework will enable simulations of quantum many-body interactions in systems with hundreds and thousands of atoms. The results will provide a detailed understanding of how composition, environment, and the degree of intermolecular interactions affect the properties of organic (opto)electronic systems. Effectively, this research bridges theoretical chemistry and the condensed-matter physics research areas. This multifaceted approach is integrated into graduate and undergraduate training, as well as newly developed K-12 outreach activities.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.