Relativistic equation-of-motion coupled-cluster method for the double ionization potentials of the closed-shell atoms

TL;DR

This paper introduces a relativistic equation-of-motion coupled-cluster method for calculating double ionization potentials, demonstrating high accuracy and comparing results with other theoretical approaches and experimental data.

Contribution

The paper presents a novel implementation of a relativistic EOM-CC method for double ionization spectra of atoms and molecules, achieving improved accuracy over previous methods.

Findings

Achieved ~0.1% accuracy in ionization potentials for selected atoms.

Compared EOM-CC results with NIST data and other ab initio methods.

Demonstrated the method's effectiveness for closed-shell atoms.

Abstract

We report the general implementation of the relativistic equation-of-motion coupled-cluster method to calculate double ionization spectra (DI-EOMCC) of atomic and molecular systems. As a first application, this method is employed to calculate the principal valence double ionization potential values of He and alkaline earth metal (Be, Mg, Ca, Sr and Ba) atoms. Our results are compared with the results available from the national institute of standards and technology (NIST) database and other ab initio calculations. We have achieved an accuracy of ~ 0.1%, which is an improvement over the first principles T-matrix calculations [J. Chem. Phys. 123, 144112 (2005)]. We also present results using the second-order many-body perturbation theory and the random- phase approximation in the equation-of-motion framework and these results are compared with the DI-EOMCC results.