Is CCSD(T) a proper standard for dipole moment calculations? An analysis considering diverse diatomic species

TL;DR

This study evaluates the accuracy of CCSD(T) for calculating ground state dipole moments of diatomic molecules at the CBS limit, comparing results with experimental data to assess its reliability as a standard.

Contribution

It provides a comprehensive analysis of CCSD(T)'s performance across diverse diatomic species, highlighting its limitations especially with transition metal molecules.

Findings

Core-correlations improve agreement with experiments for some molecules.

CCSD(T) deviations are significant for molecules with transition metals.

CCSD(T) may not be a universally reliable standard for dipole moments.

Abstract

Coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] has been extensively employed as the reference method in benchmarking different quantum chemistry methods. In this work, we test the accuracy of CCSD(T) calculating ground state electric dipole moments at the extrapolated complete basis set (CBS) limit. The calculated dipole moments have been compared to an experimental dataset consisted of diatomic molecules with various kinds of bond natures and spin configurations. As a result, to reach a satisfactory agreement with experimental dipole moments, core-correlations should be included for some molecules. However, even when core-correlations are included, the predicted dipole moment deviates considerably from the experimental values for molecules involving transition metal atoms.