Relativistic equation-of-motion coupled-cluster method using open-shell reference wavefunction

TL;DR

This paper presents a successful implementation of a relativistic equation-of-motion coupled-cluster method for open-shell systems, accurately calculating ionized states of heavy atoms and molecules by considering relativistic and electron correlation effects.

Contribution

The paper introduces a four-component relativistic EOM-CC method for open-shell systems, demonstrating its accuracy on heavy atomic and molecular ionization states.

Findings

High agreement with experimental data for heavy atoms and molecules.

Relativistic and electron correlation effects are both crucial for accurate results.

Method validation through comparison with other theoretical approaches.

Abstract

The open-shell reference relativistic equation-of-motion coupled-cluster method within its four-component description is successfully implemented with the consideration of single- and double- excitation approximation. The one-body and two-body matrix elements required for the correlation calculation are generated using Dirac-Coulomb Hamiltonian. As a first attempt, the implemented method is employed to calculate a few of the low-lying ionized states of heavy atomic (Ag, Cs, Au, Fr, Lr) and valence ionization potential of molecular (HgH, PbF) systems, where the effect of relativity does really matter to obtain highly accurate results. Not only the relativistic effect, but also the effect of electron correlation is crucial in these heavy atomic and molecular systems. To justify the fact, we have taken two further approximations in the four-component relativistic equation-of-motion framework to quantify how the effect of electron correlation plays a role in the calculated values at different level of the approximation. All these calculated results are compared with the available experimental data as well as with other theoretically calculated values to judge the extent of accuracy obtained in our calculations. A nice agreement is achieved for all the considered systems which validates the performance of the open-shell reference relativistic equation-of-motion coupled-cluster method.