Theoretical Methods For Molecular Potential Energy Surfaces and Properties

这项研究项目涉及分子电子结构理论中的三种具体计算方法，得到了美国国家科学基金会理论和计算化学项目的支持。主题(1)将Pulay目前的无限制自然轨道完全活性空间方法(UNO-CAS)扩展到大分子(例如含有24个非氢原子的分子)，并提供了更准确的激发电子态描述。主题(2)通过放宽参考函数，有效地包含了低阶广义Moller Plesset微扰理论中的高阶修正。主题(3)使用规范不变原子轨道从头算量子力学计算核磁共振性质，并探索在密度泛函理论中使用类似的技术。实验室实验和理论预测，使用基于电子运动的量子力学方程的计算机模型，今天作为平等的合作伙伴，为理解化学行为做出了贡献。现代分子电子结构计算方法的发展对几乎所有化学领域都产生了重大影响，从研究地球大气中的小分子到具有生物化学重要性的大分子。这些数学方法的发展和大规模计算机程序的实现是数百年人类努力的结果。该项目延续了开发实用的、广泛适用的理论工具的传统。这个项目的目标是提高分子电子结构计算的速度和精度，将这些计算扩展到更大的分子，处理激发电子态(对光学性质和某些类别的化学反应很重要)，并更好地了解分子结构和观测到的核磁共振(核磁共振)谱之间的基本关系。

This research project, which treats three specific computational methods in molecular electronic structure theory, is supported by the NSF Theoretical and Computational Chemistry Program. Topic (1) extends Pulay's current Unrestricted Natural Orbital Complete Active Space method (UNO-CAS) to large molecules (e.g. molecules with 24 nonhydrogen atoms) and provides a more accurate description of excited electronic states. Topic (2) effectively includes higher-order corrections in low-order Generalized Moller Plesset perturbation theory by relaxing the reference function. Topic (3) employs gauge-invariant atomic orbitals for ab initio quantum mechanical calculation of NMR properties, and explores the use of similar techniques in density functional theory. Laboratory experiments and theoretical predictions, using computer models based on the quantum mechanical equations of motion of the electrons, today contribute as equal partners to the understanding of chemical behavior. The evolution of modern methods for molecular electronic structure computation has had a major impact on virtually every field of chemistry from the study of small molecules in the earth's atmosphere to large molecules of biochemical importance. The development of these mathematical methods and their implementation into large scale computer programs is the result of hundreds of man years of effort. This project continues this tradition of developing practical, widely applicable, theoretical tools. The goal of this project is to improve the speed and accuracy of molecular electronic structure computations, to extend these to larger molecules, to treat excited electronic states (important for optical properties and certain classes of chemical reactions), and to better understand fundamental relationships between molecular structure and observed nuclear magnetic resonance (NMR) spectra.