Effects of core-valence and core-core correlation on the line strength of the resonance lines in Li i and Na i

Abstract
The resonance lines in Li I and Na I both exhibit a puzzling discrepancy between experiment and accurate ab initio calculations. Only results from a semiempirical method, that in principal neglects core-core correlation, agree with the experiments. The agreement with a multiconfiguration Hartree-Fock calculation, including only core-valence correlation, shows that this might be fortuitous. A method for including some core-core correlation is designed and gives results in excellent agreement with other accurate ab initio methods