Molecular Electronic Structure Theory: Methods and Applications

佐治亚大学的Henry(Fritz)Schaefer得到了化学部化学理论、模型和计算方法计划以及计算和数据启用科学与工程计划(CDS&amp；E)的支持，以开发新的量子化学方法来研究电子在分子中的行为。原子和分子中的电子负责形成和断裂化学键。非常小的粒子，如电子，遵循量子力学定律。因此，量子化学或电子结构方法对于基本理解化学反应以及其他重要的原子和分子过程是必不可少的。量子力学的基本方程--薛定谔方程是在计算机上求解的。除了最小的分子外，对所有分子的精确量子力学描述都需要大量的计算机时间。量子化学家的一个目标是开发更高效、更准确的方法。Schaefer和他的同事开发了一种重要的新方法，称为密度累积量理论。(DCT)这个研究项目有两个截然不同但又相互关联的目标。首先是DCT方法的假设、制定、开发、实施和检验。其次，这些新技术被用来解决重要的典型化学问题。这些方法是在一个名为PSI4的公开可用、用户友好的量子化学软件包中实现的。目前PSI4的许多开发者目前都是Schaefer研究小组的成员。在Schaefer实验室，一种重要的新方法--密度累积量理论(DCT)正在得到发展。更具体地说，所追求的是(1)来自么正变换分析的N可表示条件；(2)来自两粒子密度矩阵的幂等性的N可表示条件；(3)使用不可约压缩薛定谔方程的替代DCT谱系；(4)DCT中的三电子关联效应；以及(5)用于大规模化学应用的使用对自然轨道的有效DCT实现。同样需要解决的还有针对超大型分子系统的线性缩放算法。免费提供的、开源的PSI4套下一代电子结构理论计算机程序正在开发和分发中。从物理和材料到无机、有机和生物化学的应用正在用最先进的理论方法成功地完成。

Henry (Fritz) Schaefer of the University of Georgia is supported by an award from the Chemical Theory, Models and Computational Methods Program in the Chemistry Division and the Computational and Data-Enabled Science and Engineering Program (CDS&E) to develop new quantum chemistry methods to study the behavior of electrons in molecules. The electrons in atoms and molecules are responsible for making and breaking chemical bonds. Very small particles, such as electrons, follow the laws of quantum mechanics. Thus, quantum chemistry or electronic structure methods are essential for a fundamental understanding of chemical reactions as well as other important atomic and molecular processes. The basic equation of quantum mechanics, the Schroedinger equation, is solved on a computer. An exact quantum mechanical description of all but the smallest molecules would require vast amounts of computer time. A goal of quantum chemists is to develop more efficient and more accurate methods. Schaefer and his co-workers have developed important new methods called Density Cumulant Theory. (DCT) This research project has two, distinct but related aims. The first is the hypothesis, formulation, development, implementation, and testing of the DCT method. Second, these new techniques are used to solve important prototypical chemical problems. These methods are implemented in a publicly available, user-friendly quantum chemistry software package called PSI4. Many of the current developers of PSI4 are currently members of Schaefer's research group. In the Schaefer laboratory, an important new method is being developed, Density Cumulant Theory (DCT). More specifically being pursued are (1) N-representability conditions from analyses of unitary transformations; (2) N-representability from the idempotency of the two-particle density matrix; (3) alternative DCT hierarchies using the irreducible contracted Schroedinger equation; (4) three-electron correlation effects in DCT; and (5) efficient DCT implementations using pair natural orbitals for large scale chemical applications. Also being tackled are linear-scaling algorithms for very large molecular systems. The freely available, open-source PSI4 suite of next generation computer programs for electronic structure theory is being developed and distributed. Applications ranging from physical and materials to inorganic, organic and biological chemistry are successfully being completed with state-of-the-art theoretical methods.