Relativistic coupled-cluster-theory analysis of unusually large correlation effects in the determination of gj factors in Ca+

Abstract

We investigate roles of electron correlation effects in the determination of the gj factors of the 4s 2 S 1/2 , 4p 2 P 1/2 , 4p 2 P 3/2 , 3d 2 D 3/2 , and 3d 2 D 5/2 states, representing to different parities and angular momenta, of the Ca + ion. Correlation contributions are highlighted with respect to the mean-field values evaluated using the Dirac-Hartree-Fock method, relativistic second order manybody theory, and relativistic coupled-cluster (RCC) theory with the singles and doubles approximation considering only the linear terms and also accounting for all the non-linear terms. This shows that it is difficult to achieve reasonably accurate results employing an approximated perturbative approach. We also find that contributions through the non-linear terms and higher-level excitations such as triple excitations, estimated perturbatively in the RCC method, are found to be crucial to attain precise values of the gj factors in the considered states of Ca + ion.

Diverse trends of electron correlation effects for properties with different radial and angular factors in an atomic system: a case study in Ca+

“…In this point of view, we do not focus on the basis size truncation error and numerical instabilities. Such analyses are already carried out in our previous studies in most of the considered properties [15,26,28,40,41]. However, we would like to demonstrate importance of the higher-level excitations contributions that are neglected in the CCSD method approximations in the determination of various properties in Ca + .…”

“…The electron correlation effects hardly play any role in estimating the g J Q D correction [28], so the angular and radial dependencies of the expression given by equation (5) is reflected in the determination of the g J factor through different many-body methods.…”

Significance of Non-Linear Terms in the Relativistic Coupled-Cluster Theory in the Determination of Molecular Properties

“…It owes the title to its ability to capture electron correlation effects to a much better extent than other well-known many-body approaches such as configuration interaction (CI) [3], at a given level of truncation. This feature has led to accurate calculations of many properties in both the atomic and molecular systems (for example, see [4,5]). We shall focus on the application of this method to evaluate molecular properties that are useful to probe fundamental physics, specifically the permanent electric dipole moment (PDM) and parity and time-reversal violating electric dipole moment of the electron (eEDM) [6,7].…”