Study of quadrupole polarizabilities with combined configuration interaction and coupled-cluster method

TL;DR

This paper extends a combined configuration interaction and coupled-cluster method to accurately calculate quadrupole polarizabilities for Mg and Si^{2+}, providing precise values and analyzing their differences.

Contribution

The study applies and validates an advanced computational approach for quadrupole polarizabilities in divalent systems, achieving high accuracy and uncertainty estimates.

Findings

Calculated quadrupole polarizabilities for Mg and Si^{2+} with 0.37% accuracy.

Provided upper bounds on the uncertainty of the polarizability values.

Discussed differences in polarizability contributions between neutral Mg and Si^{2+}.

Abstract

The recently developed method combining the configuration interaction and the coupled-cluster method was demonstrated to provide accurate treatment of correlation corrections in divalent atomic systems [M.S.Safronova, M.G.Kozlov, and C.W.Clark, Phys. Rev. Lett. 107, 143006 (2011)]. We have extended this approach to the calculation of quadrupole polarizabilities alpha_2 and applied it to evaluate alpha_2 for the ground state of Mg and Mg-like Si^{2+}. Performing the calculations in three different approximations of increasing accuracy allowed us to place the upper bounds on the uncertainty of the final results. The recommended values alpha_2(3s^2 1S0)= 35.86(13) a.u. for Si^{2+} and alpha_2(3s^2 1S0)= 814(3) a.u. for Mg are estimated to be accurate to 0.37%. Differences in quadrupole polarizability contributions in neutral Mg and Si^{2+} ion are discussed.