# Fast configuration-interaction calculations for nobelium and ytterbium

## TL;DR

This paper introduces an efficient configuration-interaction method to calculate excitation energies of nobelium and ytterbium, aiding spectral predictions and experimental interpretation for these complex atoms.

## Contribution

The paper develops and tests a novel, efficient many-electron configuration-interaction approach for heavy atoms with open f-shells, specifically applied to nobelium and ytterbium.

## Key findings

- Accurate excitation energies for nobelium's low states were obtained.
- The method was validated on ytterbium, showing reliable results.
- Results assist in spectral prediction and experimental analysis for nobelium.

## Abstract

We calculate excitation energies for low states of nobelium, including states with open $5f$ subshell. An efficient version of the many-electron configuration-interaction method for treating the atom as a sixteen external electrons system has been developed and used. The method is tested on calculations for ytterbium which has external electron structure similar to nobelium. The results for nobelium are important for prediction of its spectrum and for interpretation of recent measurements. Ytterbium is mostly used to study the features of the method.