Spin-orbit coupling matrix elements from the explicitly connected expressions of the response functions within the coupled-cluster theory

TL;DR

This paper introduces a coupled cluster-based method for calculating spin-orbit coupling matrix elements using quadratic response functions, tested on alkaline earth atoms with promising results.

Contribution

The work develops a new coupled cluster response function approach for spin-orbit coupling, including systematic approximations at CCSD and CC3 levels.

Findings

Accurate spin-orbit matrix elements computed for Ca, Sr, Ba atoms.

Method shows good agreement with experimental and theoretical data.

Applicable with Gaussian and Slater basis sets.

Abstract

In this work we present a coupled cluster based approach to the computation of the spin orbit coupling matrix elements. The working expressions are derived from the quadratic response function with the coupled cluster parametrization, using the auxiliary excitation operator S. Systematic approximations are proposed with the CCSD and CC3 levels of theory. The new method is tested by computing lifetimes of several electronic states of Ca, Sr and Ba atoms, with Gaussian and Slater basis sets. The results are compared with available theoretical and experimental data.