Lower Bounds and Estimation of Energy Eigenvalues in a Gaussian Basis

摘要

Lower bounds to the groundhyphen;state energy of the helium atom are computed in the Gaussian framework. Comparison is made between the lower bounds obtained using variationally optimized upperhyphen;bound wavefunctions and the best lower bounds obtained by complete optimization of all parameters. There is a large improvement in the latter. Conroy's method of estimating eigenvalues is tested for the first time in a Gaussian basis, giving relatively poor results. An alternative method of estimating eigenvalues, based upon the partitioning of spectral impurities, is presented. The results of computations with this method are seen to be quite good.