SusChEM: Stochastic Bethe-Salpeter Approach to Excited States in Large Molecules and Nanocrystals

加州大学伯克利分校的Eran Rabani教授得到了化学系（CHE）的化学理论，模型和计算方法以及大分子，超分子和纳米化学课程的支持，以及材料研究部（DMR）的凝聚态和材料理论课程，以开发理论和计算方法来研究大分子和纳米级系统中的电子激发态。人们对开发新的纳米结构材料如纳米晶体、纳米棒及其复合材料用于光捕获和能量存储装置有着极大的兴趣，其最终目标是制造轻质和高效的装置。然而，缺乏预测工具来描述这种系统的物理特性一直是设计具有定制特性的纳米材料的主要瓶颈之一。 Rabani和他的同事试图通过精确描述激发电子态来解决这个问题，在扩展系统中所谓的“电子空穴激发”是一个相当具有挑战性的理论/计算任务。因此，本研究的目标是开发一种方法来描述激子能级排列和吸收光谱，其计算复杂性可扩展到纳米尺度的实验相关系统。这是本方案的主要目标。 研究生和博士后研究人员参与了这项研究，并正在接受尖端理论和计算方法的培训。为了降低描述光激发态的计算复杂性，Rabani和他的研究小组正在开发一种基于Bethe-Salpeter方程的实时形式化，这是描述扩展系统中激发态的最准确方法之一。Bethe-Salpeter方法在凝聚态物理学中相当流行，但在化学中未得到充分利用。实时形式主义允许他们将计算缩放减少到立方，这是一个显着的改进，但对于扩展系统来说还不够。 因此，为了进一步降低计算成本，将努力开发一个随机配方的基础上依赖于时间的描述的Bethe-Salpeter方法，导致二次缩放系统的大小。为了测试新的形式主义的准确性，预测的时间依赖性随机贝特-萨尔彼得方法将与实验测量的纳米晶体，纳米棒，和不同尺寸的种子纳米棒的数量进行比较。 如果成功，这些努力将使贝特-萨尔彼得方法成为描述扩展分子系统中激发态的方便工具，就像含时密度泛函理论是小分子系统中激发态的方便工具一样。

Professor Eran Rabani of the University of California, Berkeley is supported by the Chemical Theory, Models and Computational Methods and the Macromolecular, Supramolecular and Nanochemistry programs in the Chemistry Division (CHE) and the Condensed Matter and Materials Theory program in the Division of Materials Research (DMR)to develop theoretical and computational approaches to study electronically excited states in large molecular and nanoscale systems. There is significant interest in the development of new nanostructured materials such as nanocrystals, nanorods and their composites for light harvesting and energy storage devices, with the ultimate goal of fabricating lightweight and high efficiency devices. However, the lack of predictive tools to describe the physical properties of such systems has been one of the major bottlenecks in the design of nanomaterials with tailored properties. Rabani and his coworkers seek to address this problem by working toward an accurate description of excited electronic states, so-called "electron-hole excitations" in extended systems a rather challenging theoretical/computational task. It is therefore the goal of this research to develop a means to describe the excitonic level alignment and the absorption spectrum with computational complexity that is scalable to systems of experimental relevance at the nanometer scale. This is the major goal of the present program. Graduate students and postdoctoral research associates are involved in this research and are being trained in cutting edge theoretical and computational methods.To reduce the computational complexity of describing optically excited states, Rabani and his research group are developing a real-time formalism based on the Bethe-Salpeter equation, one the most accurate methods to describe excited states in extended systems. The Bethe-Salpeter approach is rather popular in condensed matter physics but has been underused in chemistry. The real-time formalism allows them to reduce the computational scaling to cubic, which is a significant improvement but not sufficient for extended systems. Thus, to further reduce the computational cost, efforts will be made to develop a stochastic formulation based on the time-dependent description of the Bethe-Salpeter approach, leading to quadratic scaling with system size. To test the accuracy of the new formalism, predictions made by the time-dependent stochastic Bethe-Salpeter approach will be compared with experimental measured quantities on nanocrystals, nanorods, and seeded nanorods of varying dimensions. If successful, these efforts will make the Bethe-Salpeter approach a handy tool to describe excited states in extended molecular systems in much the same way that time-dependent density functional theory is a handy tool for excited states in small molecular systems.