A Computational Study of the Vibrational and Rotational g-Factors of the Diatomic Molecules LiH, LiF, CO, CS, SiO and SiS

TL;DR

This study calculates vibrational and rotational g-factors of diatomic molecules using advanced quantum chemistry methods, comparing theoretical results with experimental data to identify the most accurate computational approaches.

Contribution

It provides a comprehensive benchmark of various computational methods and basis sets for accurately determining g-factors in diatomic molecules.

Findings

MCSCF method with aug-cc-pCV5Z basis set yields most reliable results

Vibrational averaging improves agreement with experimental g-factors

Active space size does not always converge to experimental values

Abstract

The purpose of this article is to present theoretical values for the vibrational and rotational g-factors of several diatomic molecules. The calculations have been carried out at the Multi-Configurational Self-Consistent Field (MCSCF) level of theory. To determine the most reliant method and basis set for these calculations also the Hartree-Fock (HF) and Density Functional Theory (DFT) approaches were considered. Different DFT functionals, including B3LYP, BHandHLYP, PBE0, B3PW91 and KT3 have been employed. Furthermore, different active spaces were evaluated to optimize MCSCF. To establish the accuracy of the methods the computed rotational g-factors were compared to experimental values. The benchmark study of CO and CS shows that the MCSCF method provides most reliable results and that the aug-cc-pCV5Z basis set is the most sufficient. The aug-cc-pCVQZ basis set for Li and aug-cc-pV5Z basis set for H gave best results for LiH. The active spaces tested for CO and CS do not yet converge towards the experimental values when more determinants were included. However, if the g-factors are vibrationally averaged, the computed values are seen to move towards the experimental value. Lastly, the g-factors have been vibrationally averaged, and it shows a slight improved agreement between computed values and experimental data.