# Shape resonances of Be$^-$ and Mg$^-$ investigated with method of analytic continuation

## TL;DR

This paper applies a regularized analytic continuation method to accurately compute low-energy resonance states of Be$^-$ and Mg$^-$ ions using routine quantum chemistry calculations, demonstrating good agreement with advanced methods.

## Contribution

It introduces a simple, accessible approach for calculating atomic negative ion resonances using regularized analytic continuation with standard quantum chemistry software.

## Key findings

- Resonance parameters for Be$^-$ and Mg$^-$ agree with advanced methods.
- The method is stable with respect to perturbation width and input range.
- Resonance energies and widths are accurately determined.

## Abstract

The regularized method of analytic continuation is used to study the low-energy negative ion states of beryllium (configuration 2$s^2\varepsilon p\; ^2P$) and magnesium (configuration 3$s^2\varepsilon p\; ^2P$) atoms. The method applies an additional perturbation potential and it requires only routine bound-state multi-electron quantum calculations. Such computations are accessible by most of the free or commercial quantum chemistry software available for atoms and molecules. The perturbation potential is implemented as a spherical Gaussian function with a fixed width. Stability of the analytic continuation technique with respect to the width and with respect to the input range of electron affinities is studied in detail. The computed resonance parameters $E_r$=0.282 eV, $\Gamma$=0.316 eV for the $2p$ state of Be$^-$ and $E_r$=0.188 eV, $\Gamma$=0.167 for the $3p$ state of Mg$^-$, agree well with the best results obtained by much more elaborated and computationally demanding present-day methods.