Development of Programs for Spin Projection, Energy Derivatives and Advanced Graphics in MO Calculations

该项目是由理论和计算物理化学计划中的计算科学和工程倡议资助的。施莱格尔教授的目标是开发快速计算化学反应反应路径的技术，以及准确的能垒和断键能量的理论预测。这项工作，以及施莱格尔教授之前的工作，预计将对实验化学家有很大的帮助。当不受限制的Hartree-Fock和Moeller-Plesset微扰理论用于开壳系统的反应和键的解离时，来自不想要的自旋态的污染有时可能大到足以严重扭曲能面。最大自旋污染物的湮灭极大地提高了计算的势垒高度和键离解势。本项目将涉及所有自旋污染物的湮灭，自旋投射能量梯度的计算，用于关联修正的自旋湮没，以及用于测试自旋投射方法的全CI和高阶微扰理论。证明自旋投射方法实用性的化学应用将包括研究多个键的自由基加成，自由基提取反应，键解离势，以及环加成反应中的双自由基中间体。还将开发用于自旋投射能量梯度、过渡态优化、反应路径跟踪、使用解析梯度的基组优化以及使用电场相关函数的IR强度的新算法。

This project is being funded under the Computational Science and Engineering Initiative in the Theoretical and Computational Physical Chemistry program. Professor Schlegel's aim is to develop techniques for rapid calculation of reaction pathways for chemical reactions and the accurate theoretical prediction of energy barriers and bond- breaking energies. This work, and prior work by Professor Schlegel, are expected to be of great utility to experimental chemists. When unrestricted Hartree-Fock and Moeller-Plesset perturbation theory are used for reactions of open shell systems and for bond dissociations, contamination from unwanted spin states can sometimes be large enough to distort the energy surface severely. Annihilation of the largest spin contaminant dramatically improves calculated barrier heights and bond dissociation potentials. The present project will address the annihilation of all spin contaminants, calculation of gradients of spin-projected energies, spin annihilation applied to correlation corrections, and full CI and high order perturbation theory to test the spin projected methods. Chemical applications to demonstrate the utility of the spin projected method will include studies of radical additions to multiple bonds, radical abstraction reactions, bond dissociation potentials, and diradical intermediates in cycloaddition reactions. New algorithms will also be developed for gradients of spin projected energies, transition state optimization, reaction path following, basis set optimization using analytical gradients, and IR intensities using electric field-dependent functions.