New Developments and Applications in Coupled Clusters and Density Dependent Electronic Structure Methods

这项研究得到了美国国家科学基金会理论和计算化学项目的支持。对分子电子结构理论中的耦合团簇方法和密度泛函方法进行了研究和比较，以寻求密度泛函理论的从头算衍生泛函。本文将探索一种计算Brueckner偶理论中三重微扰修正的改进方案。这些计算方法将应用于过渡金属体系和燃烧过程的研究。理论上，分子体系的物理化学性质可以由多体波函数(传统的从头算理论)或电子电荷密度(密度泛函理论)获得。目前存在高度发展的计算机程序，用于将这两种理论中的任何一种应用于各种化学问题中的任何一种。从头算方程，特别是那些耦合星系团理论的方程，可能需要使用超级计算机进行非常繁重的计算，但这些方程牢牢地基于良好的数学和物理原理。密度泛函理论的方程提供了显著的计算优势，但这些方程的精确形式仍然存在严重的问题。目前对从头算方法和密度泛函方法的比较研究试图开发结合这两种不同形式的优点的分子电子结构计算的改进计算方法。发展这种改进的密度泛函理论是当前理论化学的一个热点问题。这一领域的突破将极大地扩大分子体系的规模，这些分子体系可以用现代计算机做出可靠的理论预测，并几乎肯定会得到广泛和立即的应用。拟议的过渡金属化合物测试计算是朝着合理设计新的工业催化剂迈出的第一步。

This research is supported by the NSF theoretical and computational chemistry program. Coupled-cluster and density functional methods in molecular electronic structure theory will be studied and compared to search for an ab-initio-derived-functional for density functional theory. An improved scheme will be explored for computing the triples perturbative correction in Brueckner doubles theory. These computational methods will be applied to the study of transition metal systems and combustion processes. In principle, the physical and chemical properties of molecular systems can be obtained from either the many-body wavefunction (traditional ab initio theory) or from the electronic charge density (density functional theory). There presently exist highly developed computer programs for applying either of these two theories to any of a wide variety of chemical problems. Ab initio equations, particularly those of coupled cluster theory, may require very heavy computations using supercomputers, but these equations are firmly based on well established mathematical and physical principles. The equations of density functional theory offer significant computational advantages, but serious questions remain concerning the precise form of these equations. The present comparative study of ab initio and density functional methods attempts to develop improved computational methods for molecular electronic structure computations which combine the strengths of these two different formalisms. The development of such an improved density functional theory is currently a hot topic in modern theoretical chemistry. A breakthrough in this area will greatly extend the size of molecular systems for which reliable theoretical predictions can be made using modern computers, and will almost certainly find wide and immediate application. The proposed test calculations on transition metal compounds constitute the initial steps toward the rational design of new industrial catalysts.