Advances in Coupled-Cluster Theory with Molecular Applications

佛罗里达大学的约翰·斯坦顿得到了化学系化学理论、模型和计算方法项目的支持。斯坦顿和他的研究小组从事理论化学物理领域的工作，该领域旨在将物理学的概念应用于原子和分子的研究。他们在两个研究领域工作：量子化学和分子动力学。在量子化学中，斯坦顿小组开发并应用了处理电子的方法类别中的计算工具，这种方法被称为耦合团簇理论，能够高度准确地计算实验者感兴趣的分子的性质。在分子动力学中，他们发展了半经典过渡态理论的方法，使预测和理解化学反应发生的速度成为可能。量子化学研究的潜在应用包括非常详细的计算，以提高研究大气和工业中化学过程的化学模型的保真度。通过将量子化学的工作与反应速率理论的发展相结合，他们可以对涉及自由基和双自由基的化学反应进行准确的研究。后一领域的研究在许多领域都具有重要意义，因为对生命至关重要、占大气20%的氧分子是双自由基。本研究中开发的量子化学方法都在CFOUR量子化学程序包中实现，该程序包可以免费提供给研究界。斯坦顿正致力于在他的大学里为学习自然科学的高积极性和高成就的学生开发一个荣誉项目。拟议的研究涉及电子关联的耦合集群处理方面的探索，特别是涉及高精度方法，包括四重激发的影响和多参考效应，这是无处不在的(也是重要的)一类问题的特征，组成了“双自由基”系统。此外，我们还将探索半经典过渡态理论的精确度和局限性，包括：与多维模型系统的精确量子结果进行比较，设计该方法的扩展，以及探索用该方法处理的伪态与Siegert本征态之间的形式联系。此外，还将致力于开发包括角动量效应在内的分子中振动耦合的处理方法，最终设计和实施自旋-共振子处理。

John Stanton of the University of Florida is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry. Stanton and his research group work in the field of theoretical chemical physics, which aims to apply concepts from physics to the study of atoms and molecules. They work in two research areas: quantum chemistry and molecular dynamics. In quantum chemistry, the Stanton group develops and applies computational tools from the class of methods for treating electrons that is known as coupled-cluster theory to enable highly accurate calculations of the properties of molecules that are of interest to experimentalists. In molecular dynamics, they develop approaches to semiclassical transition state theory, enabling the prediction and understanding of the rates at which chemical reactions take place. Potential applications of the quantum chemistry research include very detailed calculations to improve the fidelity of chemical models to study chemical processes in the atmosphere and industry. By combining the work in quantum chemistry with the reaction rate theory developments, they can perform accurate studies of chemical reactions involving radicals and biradicals. This latter area of research has significant import in many areas, since the oxygen molecule so vital to life and which constitutes 20% of the atmosphere is a biradical. The quantum chemistry methods that are developed in this research are all implemented in the CFOUR quantum chemistry package, which is freely available to the research community. Stanton is working to develop an honors program at his university for highly-motivated and highly-accomplished students enrolled in the study of the natural sciences.The proposed research involves explorations in the coupled-cluster treatment of electronic correlation, specifically involving high-accuracy methods including effects of quadruple excitations and the multireference effects that are characteristic of the ubiquitous (and important) class of problems that comprise "biradical" systems. In addition, work will be done to explore the accuracy and limits of semiclassical transition state theory, involving: benchmarking against exact quantum results for multidimensional model systems, designing extensions of the method, and exploring the formal connections between the pseudo-states treated by this method and Siegert eigenstates. In addition, work will be done on developing methods for the treatment of vibronic coupling in molecules that include angular momentum effects, culminating in the design and implementation of a spin-rovibronic treatment.