Dipole Polarizability Calculation of Cd Atom: Inconsistency with experiment

TL;DR

This study calculates the dipole polarizability of the Cd atom using advanced relativistic coupled-cluster methods, resolving previous discrepancies with experimental data by employing the relativistic normal coupled-cluster approach and finite-field calculations.

Contribution

The paper introduces the use of the relativistic normal coupled-cluster (RNCC) method for more accurate polarizability calculations of Cd, addressing inconsistencies in earlier theoretical approaches.

Findings

Calculated $oldsymbol{ ext{α}_d}$ as 46.02(50) e a₀³, aligning closely with experimental values.

Demonstrated the importance of triples excitations in accurate polarizability calculations.

Showed RNCC method's advantages, including natural termination of expectation value expressions and adherence to Hellmann-Feynman theorem.

Abstract

Three earlier relativistic coupled-cluster (RCC) calculations of dipole polarizability ($\alpha_d$) of the Cd atom are not in good agreement with the available experimental value of $49.65(1.65) \ e a_0^3$. Among these two are finite-field approaches in which the relativistic effects have been included approximately, while the other calculation uses a four component perturbed RCC method. However, another work adopting an approach similar to the latter perturbed RCC method gives a result very close to that of experiment. The major difference between these two perturbed RCC approaches lies in their implementation. To resolve this ambiguity, we have developed and employed the relativistic normal coupled-cluster (RNCC) theory to evaluate the $\alpha_d$ value of Cd. The distinct features of the RNCC method are that the expression for the expectation value in this approach terminates naturally and that it satisfies the Hellmann-Feynman theorem. In addition, we determine this quantity in the finite-field approach in the framework of A four-component relativistic coupled-cluster theory. Considering the results from both these approaches, we arrive at a reliable value of $\alpha_d=46.02(50) \ e a_0^3$. We also demonstrate that the contribution from the triples excitations in this atom is significant.