Molecular Electronic Structure Theory: Methods and Applications

乔治亚大学的Henry (Fritz) Schaefer获得了化学学部化学理论、模型和计算方法项目以及计算和数据支持科学与工程项目（CDS&amp；E）的奖励，以开发新的量子化学方法来研究分子中电子的行为。原子和分子中的电子负责形成和破坏化学键。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化学反应以及其他重要的原子和分子过程的基本理解是必不可少的。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，对所有分子进行精确的量子力学描述将需要大量的计算机时间。量子化学家的一个目标是发展更有效和更精确的方法。Schaefer和他的同事开发了重要的新方法，称为密度累积量理论。这个研究项目有两个不同但又相关的目标。首先是DCT方法的假设、制定、发展、实施和测试。其次，这些新技术被用于解决重要的典型化学问题。这些方法是在一个公开可用的、用户友好的量子化学软件包PSI4中实现的。目前PSI4的许多开发人员都是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）正在被开发。更具体地追求的是(1)从分析幺正变换得出的n -可表征性条件；(2)由两粒子密度矩阵的幂等得到n -可表示性；(3)利用不可约收缩薛定谔方程的可选DCT层次；(4) DCT中的三电子相关效应；(5)大规模化学应用中使用对自然轨道的高效DCT实现。同时正在研究的是用于非常大的分子系统的线性缩放算法。电子结构理论的下一代计算机程序PSI4套件正在开发和分发。应用范围从物理和材料到无机，有机和生物化学都成功地完成了最先进的理论方法。

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.