Exponentially correlated Hylleraas-Configuration Interaction studies of atomic systems. II. Non-relativistic energies of the 1 singlet S through 6 singlet S states of the Li+ ion

Published

October 15, 2021

Author(s)

Maria B. Ruiz, James S. Sims, Bholanath Padhy

Abstract

A generalization of the Hylleraas-Configuration Interaction method (Hy-CI) first proposed in a previous study, the Exponentially Correlated Hylleraas-Configuration Interaction method (E-Hy-CI) in which the single rij of an Hy-CI wave function is generalized to a form of the generic type rij exp(-a rij), is explored. This type of correlation, suggested by Hirschfelder in 1960, has the right behavior both in the vicinity of the rij cusp as rij goes to 0 and as rij goes to infinity; this work continues the exploration, begun in the first paper in this series (on the helium atom), of whether wave functions containing both linear and exponential rij factors converge more rapidly than either one alone. In the present study we examine not only the ground 1 singlet S state of the Li+ ion, but the 2 singlet S through 6 singlet S excited states as well. The convergence of the E-Hy-CI wave function expansion is compared with that of the Hy-CI wave function without exponential factors for excited S states, demonstrating again both convergence acceleration and an improvement in the precision for the same basis. This makes the application of the E-Hy-CI method to systems with N > 4, for which this formalism with at most a single rij exp(-a rij) factor per term leads to solvable integrals, very promising.

Citation

International Journal of Quantum Chemistry

Volume

122

Issue

1

Pub Type

Journals

Download Paper

https://doi.org/10.1002/qua.26823

Local Download

Keywords

Lithium ion, non-relativistic energy, singlet S states, Hy-CI, E-Hy-CI

Citation

Ruiz, M. , Sims, J. and Padhy, B. (2021), Exponentially correlated Hylleraas-Configuration Interaction studies of atomic systems. II. Non-relativistic energies of the 1 singlet S through 6 singlet S states of the Li+ ion, International Journal of Quantum Chemistry, [online], https://doi.org/10.1002/qua.26823, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=933006 (Accessed April 24, 2024)