Combining configuration interaction with perturbation theory for atoms with large number of valence electrons

TL;DR

This paper introduces a hybrid computational method combining configuration interaction with perturbation theory, enabling efficient and accurate spectral calculations for complex atoms with many valence electrons.

Contribution

A novel approach that treats highly excited states perturbatively within CI, reducing computational complexity for large-electron atoms.

Findings

Accurately calculated spectra of iodine, tungsten, and ytterbium.

Method shows good agreement with experimental data.

Discusses advantages and limitations of the combined approach.

Abstract

A version of the configuration interaction (CI) method is developed which treats highly excited many-electron basis states perturbatively, so that their inclusion does not affect the size of the CI matrix. This removes, at least in principle, the main limitation of the CI method in dealing with many-electron atoms or ions. We perform calculations of the spectra of iodine and its ions, tungsten, and ytterbium as examples of atoms with open $s$, $p$, $d$ and $f$-shells. Good agreement of the calculated data with experiment illustrates the power of the method. Its advantages and limitations are discussed.