Towards a spectroscopically accurate set of potentials for heavy hydride laser cooling candidates: effective core potential calculations of BaH

TL;DR

This study develops highly accurate ab initio potential energy surfaces for BaH, a promising laser cooling candidate, using advanced computational methods to closely match experimental data and improve simulation reliability.

Contribution

The paper demonstrates the generation of spectroscopically accurate potentials for BaH using MRCI+Q with an effective core potential, achieving close agreement with experimental molecular constants.

Findings

Predicted dissociation energy D_e within 0.1% of experimental value

Calculated r_e within 0.03 pm of experimental data

Validated the use of a 46-electron ECP with augmented basis sets for accurate predictions

Abstract

BaH (and its isotopomers) is an attractive molecular candidate for laser cooling to ultracold temperatures and a potential precursor for the production of ultracold gases of hydrogen and deuterium. The theoretical challenge is to simulate the laser cooling cycle as reliably as possible and this paper addresses the generation of a highly accurate ab initio $^{2}\Sigma^+$ potential for such studies. The performance of various basis sets within the multi-reference configuration-interaction (MRCI) approximation with the Davidson correction (MRCI+Q) is tested and taken to the complete basis set limit. It is shown that the calculated molecular constants using a 46 electron Effective Core-Potential (ECP), the augmented polarized core-valence quintuplet basis set (aug-pCV5Z-PP) but only including three active electrons in the MRCI calculation are in close agreement with the available experimental values. The predicted dissociation energy D$_e$ for the X$^2\Sigma^+$ state (extrapolated to the complete basis set (CBS) limit) is 16895.12 cm$^{-1}$ (2.094 eV), which agrees within 0.1$\%$ of a revised experimental value of $<$16910.6 cm$^{-1}$, while the calculated r$_e$ is within 0.03 pm of the experimental result.