Triple excitation in relativistic coupled-cluster theory and properties of one-valence systems Rb and Sr$^+$

TL;DR

This paper develops a tensor-based approach to include triple excitations in relativistic coupled-cluster calculations, analyzing their impact on hyperfine structure constants of Rb and Sr$^+$.

Contribution

It introduces a tensor representation of triple cluster operators and derives linearized equations for relativistic coupled-cluster theory with triples.

Findings

Triple excitations significantly affect hyperfine constants.

The tensor representation simplifies inclusion of triples.

Results improve agreement with experimental data.

Abstract

We examine the contributions from triple excitation cluster operators in the relativistic coupled-cluster theory in atoms and ions. For this, we propose a tensor representation of the triple cluster operator. Based on this representaion and using diagrammatic analysis, we derive the linearized coupled-cluster equations for single, double and triple excitation cluster operators. The contributions from the triple cluster operators to the hyper fine structure constants of single-valence systems Rb and Sr$^+$ are analysed using the perturbed triples.