CAREER: Stochastic Methods for Electronic Excitations in Complex Nanoscale System

对电子激励的定量理论理解对于研究和设计新的电子器件是必要的。这些系统的性质主要是由量子力学相互作用，延伸到纳米尺度。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，并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尺度系统，以阐明电子器件设计的新策略;及（iii）物理、化学、和材料科学，专注于凝聚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的动力学，电子-电子相互作用该方法是基于一个非确定性的量子统计方法。它在计算上是便宜的，并且它允许以高精度处理非常大的系统。该项目还提供了一种新的方法来考虑有限的温度效应。因此，有可能建立计算结果和实验观测之间的直接对应关系。该项目中开发和使用的理论工具将提供给社区。新的发展将应用于光伏系统，阐明结构和化学修饰如何影响光伏器件及其界面的电子激发。该项目的教育目标旨在为研究生，本科生以及K-12学生提供工具和培训。PI将为研究生提供理论和计算方面的研究经验。将通过这项提案与加利福尼亚州少数民族参与联盟合作，为本科生提供多种研究和培训机会。该奖项还支持一个新的教育K-12外展活动的分子和电子结构之间的关系。技术总结该职业奖支持电子激励理论的研究和教育。该研究小组将根据波函数和算子期望值的有效数值采样，开发一种随机形式的多体微扰理论。 电子-电子相互作用的表示是以绿色函数形式推导出来的，其中包括高阶相关（顶点）项。这一步是结合一个新的随机形式主义计算电子-声子耦合，这需要考虑与实验进行定量比较。 研究小组将确定最准确和有效的随机实现的多体微扰理论预测电子激发。新的发展将应用于具有强电荷转移和激子效应的有机光伏系统。这个项目将分三个步骤进行：（i）发展一个超越常用近似的精确随机多体框架，包括强电子-空穴相互作用的处理（ii）发展新的随机方法来研究振动对大系统激发能的影响;以及（iii）新的随机框架在大分子体系及其凝聚相组装中的应用。新的计算框架将能够模拟具有成百上千个原子的系统中的量子多体相互作用。结果将详细了解组成、环境和分子间相互作用程度如何影响有机（光）电子系统的特性。有效地，这项研究桥梁理论化学和凝聚态物理研究领域。这种多方面的方法被整合到研究生和本科生的培训中，以及新开发的K-12推广活动中。该奖项反映了NSF的法定使命，并被认为值得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来支持。

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.