Theoretical Methods for Molecular Potential Surfaces

理论和计算化学课程中的这个项目涉及对分子进行电子结构计算的几种改进方法的开发。在局域相关方法中将采用解析能量梯度方法，以便于大分子基态的几何确定。基于UHF自然轨道的初步计算，将一种新的无偏选择MCSCF活性轨道的方法推广到激发态。一种新的用于确定开壳和多参考态的关联能的微扰理论将被实施和检验。一种消除自旋污染的新方法也将改进基于UHF态的类比微扰理论。综上所述，这些发展将极大地扩大可以通过准确的计算方法解决的化学问题的范围。

This project in the Theoretical and Computational Chemistry program concerns the development of several improved methods for carrying out electronic structure calculations on molecules. Analytic energy gradient methods will be implemented in the Local Correlation Method to facilitate geometry determinations of the ground states of large molecules. A new method for unbiased selection of active MCSCF orbitals, based on preliminary calculation of UHF natural orbitals, will be generalized to excited states. A new perturbation theory for determination of correlation energies in open shell and multi-reference states will be implemented and tested. The analogous perturbation theory based on UHF states will also be improved by a new method of eliminating spin contamination. Taken together, these developments will greatly extend the range of chemical problems that can be addressed by accurate computational methods.