On the Breit interaction in an explicitly correlated variational Dirac-Coulomb framework

TL;DR

This paper implements the Breit interaction within an explicitly correlated variational Dirac-Coulomb framework, comparing perturbative and variational approaches, and analyzing deviations from perturbation theory for low atomic numbers.

Contribution

It introduces a method to include the Breit interaction in a no-pair variational Dirac-Coulomb framework using explicitly correlated Gaussian basis, with both perturbative and fully variational treatments.

Findings

Perturbative and variational energies are compared with perturbation theory.

Deviations from perturbation theory are analyzed and discussed.

The approach is applied to low Z atomic systems.

Abstract

The Breit interaction is implemented in the no-pair variational Dirac-Coulomb (DC) framework using an explicitly correlated Gaussian basis reported in the previous paper [Paper I: P. Jeszenszki, D. Ferenc, and E. M\'atyus (2022)]. Both a perturbative and a fully variational inclusion of the Breit term is considered. The no-pair DC plus perturbative Breit as well as the no-pair Dirac-Coulomb-Breit energies are compared with perturbation theory results including the Breit-Pauli Hamiltonian and leading-order non-radiative quantum electrodynamics corrections for low $Z$ values. Possible reasons for the observed deviations are discussed.