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

本研究由美国国家科学基金会理论与计算化学项目资助。本文将研究和比较分子电子结构理论中的耦合簇和密度泛函方法，以寻找密度泛函理论中的ab-初始推导泛函。本文将探讨一种计算布鲁克纳双重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系统和燃烧过程的研究。原则上，分子系统的物理和化学性质既可以从多体波函数（传统的从头算理论）得到，也可以从电子电荷密度（密度泛函理论）得到。目前存在着高度发达的计算机程序，可将这两种理论中的任何一种应用于各种各样的化学问题。从头算方程，特别是耦合集群理论的方程，可能需要使用超级计算机进行非常繁重的计算，但这些方程是牢固地建立在良好的数学和物理原理基础上的。密度泛函理论的方程提供了显著的计算优势，但关于这些方程的精确形式仍然存在严重的问题。目前对从头算和密度泛函方法的比较研究试图开发改进的分子电子结构计算方法，结合这两种不同形式的优势。这种改进的密度泛函理论的发展是当前现代理论化学的一个热点。这一领域的突破将极大地扩展分子系统的规模，用现代计算机可以对分子系统进行可靠的理论预测，而且几乎肯定会得到广泛而直接的应用。所提出的过渡金属化合物的试验计算是合理设计新型工业催化剂的第一步。

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.