A Comparative Analysis of Non-relativistic and Relativistic Calculations of Electric Dipole Moments and Polarizabilities of Heteronuclear Alkali Dimers

TL;DR

This study compares non-relativistic and relativistic calculations of electric dipole moments and polarizabilities in heteronuclear alkali dimers, highlighting the importance of relativistic effects for accurate predictions and their impact on Van der Waals interactions.

Contribution

It provides a comprehensive analysis of relativistic effects on molecular properties using coupled-cluster theory, improving the accuracy of theoretical predictions for alkali dimers.

Findings

Relativistic effects significantly influence PDMs more than polarizabilities.

Inclusion of relativistic PDMs improves Van der Waals $C_6$ coefficients.

Relativistic calculations align better with experimental data for PDMs.

Abstract

We analyze the molecular electric dipole moments (PDMs) and static electric dipole polarizabilities of heteronuclear alkali dimers in their ground states by employing coupled-cluster theory, both in the non-relativistic and four-component relativistic frameworks. The roles of electron correlations as well as relativistic effects are demonstrated by studying them at different levels of theory, followed by a comprehensive treatment of error estimates. We compare our obtained values with the previous non-relativistic calculations, some of which include lower-order relativistic corrections, as well as with the experimental values, wherever available. We find that the PDMs are very sensitive to relativistic effects, as compared to polarizabilities; this aspect can explain the long-standing question on the difference between experimental values and theoretical results for LiNa. We show that consideration of relativistic values of PDMs improves significantly the isotropic Van der Waals $C_6$ coefficients of the investigated alkali dimers over the previously reported non-relativistic calculations. The dependence of dipole polarizabilities on molecular volume is also illustrated.