Hylleraas-configuration-interaction analysis of the low-lying states in the three-electron Li atom and Be+ ion

TL;DR

This paper presents a highly accurate computational analysis of low-lying states in the three-electron lithium atom and beryllium ion using Hylleraas-configuration-interaction methods, achieving unprecedented precision for many excited states.

Contribution

It introduces an effective procedure for calculating energies of excited states in three-electron systems with high accuracy using compact wave functions.

Findings

Achieved approximately 1.10-6 a.u. accuracy for ground states

Achieved approximately 1.10-4 a.u. accuracy for excited states

Many excited states evaluated with unprecedented precision

Abstract

The total energies of twenty eight bound S-, P-, D-, F-, G-, H-, and I-states in the three-electron systems Li atom and Be+ ion, respectively, are determined with the use of the Configuration Interaction (CI) with Slater orbitals and L-S eigenfunctions, and the Hylleraas-configuration-interaction (Hy-CI) methods. We discuss the construction and selection of the configurations in the wave functions, optimization of the orbital exponents and advanced computational techniques. Finally, we have developed a very effective procedure which allows one to determine the energies of the excited states in three-electron atoms and ions to high accuracy by using compact wave functions. For the ground and low lying excited states our best accuracy with the Hy-CI method was approximately 1.10-6 a.u. and 1.10-4 a.u. for other excited states. Analogous accuracy of the CI method is substantially lower approximately 1.10-3 a.u. Many of the rotationally excited (bound) states in the three-electron Li atom and Be+ ion have never been evaluated to such an accuracy.