Benchmarking many-body approaches for the determination of isotope-shift constants: Application to the Li, Be+, and Ar15+ isoelectronic systems

B. K. Sahoo and B. Ohayon
Phys. Rev. A 103, 052802 – Published 4 May 2021

Abstract

We have applied relativistic coupled-cluster (RCC) theory to determine the isotope-shift (IS) constants of the first eight low-lying states of the Li, Be+, and Ar15+ isoelectronic systems. Though the RCC theory with singles, doubles, and triples approximation (RCCSDT method) is an exact method for these systems for a given set of basis functions, we notice large differences in the results from this method when various procedures in the RCC theory framework are adopted to estimate the IS constants. This has been demonstrated by presenting the IS constants of the aforementioned states from the finite-field, expectation value, and analytical response (AR) approaches of the RCCSDT method. Contributions from valence triple excitations, Breit interaction, and lower-order QED effects to the evaluation of these IS constants are also highlighted. Our results are compared with high-precision calculations reported using few-body methods wherever possible. We find that results from the AR procedure are more reliable than the other two approaches. This analysis is crucial for understanding the roles of electron correlation effects in the accurate determination of IS constants in the heavier atomic systems, where few-body methods cannot be applied.

  • Received 1 March 2021
  • Accepted 22 April 2021

DOI:https://doi.org/10.1103/PhysRevA.103.052802

©2021 American Physical Society

Physics Subject Headings (PhySH)

Atomic, Molecular & Optical

Authors & Affiliations

B. K. Sahoo1,* and B. Ohayon2,†

  • 1Atomic and Molecular Physics Division, Physical Research Laboratory, Navrangpura, Ahmedabad 380009, India
  • 2Institute for Particle Physics and Astrophysics, ETH Zürich, CH-8093 Zürich, Switzerland

  • *bijaya@prl.res.in
  • bohayon@ethz.ch

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Issue

Vol. 103, Iss. 5 — May 2021

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