Implementation and Application of the Relativistic Equation of Motion Coupled-cluster Method for the Excited States of Closed-shell Atomic Systems

TL;DR

This paper presents the implementation of a relativistic equation-of-motion coupled-cluster method for calculating excited states in closed-shell atomic systems, demonstrating its accuracy on highly charged ions relevant to astrophysics.

Contribution

The paper introduces a four-component relativistic EOMCC method for excited state calculations, enabling high-precision atomic property evaluations in complex ions.

Findings

Accurately calculated excitation energies for Ne-like ions.

Validated the method against experimental data.

Estimated sensitivity coefficients for fine structure constant variations.

Abstract

We report the implementation of equation-of-motion coupled-cluster (EOMCC) method in the four-component relativistic framework with the spherical atomic potential to generate the excited states from a closed-shell atomic configuration. This theoretical development will be very useful to carry out high precision calculations of varieties of atomic properties in many atomic systems. We employ this method to calculate excitation energies of many low-lying states in a few Ne-like highly charged ions, such as Cr XV, Fe XVII, Co XVIII and Ni XIX ions, and compare them against their corresponding experimental values to demonstrate the accomplishment of the EOMCC implementation. The considered ions are apt to substantiate accurate inclusion of the relativistic effects in the evaluation of the atomic properties and are also interesting for the astrophysical studies. Investigation of the temporal variation of the fine structure constant (\alpha) from the astrophysical observations is one of the modern research problems for which we also estimate the \alpha sensitivity coefficients in the above ions.