Theoretical Methods for Molecular Potential Surfaces

理论和计算化学计划中的该项目涉及开发几种用于对分子进行电子结构计算的改进方法。 局部相关法将采用解析能量梯度法，以促进大分子基态的几何确定。 基于 UHF 自然轨道的初步计算，一种无偏选择活性 MCSCF 轨道的新方法将推广到激发态。 将实施和测试一种用于确定开壳和多参考态相关能量的新扰动理论。 基于超高频态的类似微扰理论也将通过消除自旋污染的新方法得到改进。 总而言之，这些进展将极大地扩展可以通过精确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.