High-Level Coupled-Cluster Energetics by Monte Carlo Sampling and Moment Expansions

密歇根州立大学的Piotr Piecuch开发了一种解决多粒子薛定谔方程的全新方法，获得了化学学部化学理论、模型和计算方法项目的奖励。这种方法是解释原子和分子中电子运动的关键。通过了解这一运动的细节，Piecuch和他的团队可以精确地确定打破化学键和将反应物转化为产物所需的能量。准确地进行这些计算的能力最终将有助于设计新材料、更好的催化剂和更有效的能源。新方法对许多小能量贡献进行反复随机测试，并保留了那些发现最重要的能量贡献。该方法将高精度方法的计算成本降低了几个数量级。一旦开发完成，这些方法将通过开源机制与社区共享。这些活动的结果被用于教学课程，并通过出版物、研讨会和会议报告进行交流。这些想法为Piecuch小组成员提供了物理科学前沿的积极培训经验。本研究解决了电子结构理论中的一个关键挑战，即开发实用的和系统改进的从头计算方案，旨在准确描述分子能量学。人们普遍认为，基于耦合簇理论的尺寸扩展方法是解决这一挑战的优秀候选人。然而，众所周知，很难将集群算子的高于两体的组件合并在一起，这需要实现定量描述，而不会遇到高阶耦合集群方案的令人望而却步的计算成本。所提出的方法解决了这个问题，即使当电子准简并和高于对的激励变得重要时，也能以很小的计算成本获得相当于高水平耦合簇计算的精确能量。它还保留了传统的单参考计算的黑盒特征，通过融合确定性形式，缩写为CC（P；Q）与随机配置相互作用和耦合簇蒙特卡罗方法。形式和算法的进步以及高效的计算机实现将伴随着与光谱学、化学反应机制和动力学以及催化相关的分子势能表面的计算。这项工作为研究生和博士后提供了重要的培训，并且正在开发的项目将与更广泛的理论界广泛共享。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。

Piotr Piecuch of Michigan State University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Chemistry Division to develop a radically new approach to solving the many-particle Schrodinger equation. This method holds the key to explaining the motion of electrons in atoms and molecules. By understanding the details of this motion, Piecuch and his group can precisely determine the amounts of energy needed to break chemical bonds and transform reactants into products. The ability to do these calculations accurately will ultimately aid in the design of new materials, better catalysts, and more efficient energy sources. The new approach uses repeated random tests of many small energy contributions and retains those found to be most important. This approach reduces the computational costs of high-accuracy methods by orders of magnitude. Once fully developed, the methods will be shared with the community via open-source mechanisms. Findings resulting from the activities are being used in teaching courses and communicated through publications, seminars, and conference presentations. These ideas provide positive training experiences in the forefront of the physical sciences for members of the Piecuch group. This research addresses one of the key challenges in electronic structure theory, namely the development of practical and systematically improvable ab initio computational schemes aimed at an accurate description of molecular energetics. It is widely accepted that size extensive methods based on the coupled-cluster theory are excellent candidates for addressing this challenge. However, it has been notoriously difficult to incorporate higher-than two-body components of the cluster operator, needed to achieve a quantitative description, without running into prohibitive computational costs of higher-order coupled-cluster schemes. The proposed methodology solves the problem, allowing one to obtain accurate energetics equivalent to high-level coupled-cluster calculations, even when electronic quasi-degeneracies and higher-than pair excitations become significant, at a small fraction of the computational cost. It also preserves the black-box character of conventional single-reference computations, by fusing the deterministic formalism, abbreviated as CC(P;Q) with the stochastic configuration interaction and coupled-cluster Monte Carlo approaches. The formal and algorithmic advances and efficient computer implementations will be accompanied by calculations of molecular potential energy surfaces relevant to spectroscopy, chemical reaction mechanisms and dynamics, and catalysis. The work provides important training for graduate students and postdoctoral fellows and the programs being developed will be widely shared with the broader theoretical community.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.