Accurately solving the electronic Schrödinger equation of atoms and molecules using explicitly correlated (r12-) multireference configuration interaction. VII. The hydrogen fluoride molecule

Abstract

We compute the potential-energy curve of the hydrogen fluoride molecule (HF) using a novel variant of the explicitly correlated multireference averaged coupled-pair functional method with a carefully selected basis set and reference space. After correcting for scalar relativistic effects and spin-orbit coupling, the potential is used to compute the dissociation energy, the equilibrium bond distance, the harmonic frequency, the anharmonicity, and the vibrational levels up to the dissociation limit. The errors in the equilibrium geometry constants compare favorably with the most elaborate (single reference) calculations of the literature. Starting at the region of RA/angstroms approximately 2,...,3, where the covalent HF bond begins to break and where single-reference methods become impractical, our potential begins to slightly underestimate the atomic interaction, which is reflected in an estimated error in the well depth of -0.2 kcal/mol.