Resonating valence bond wave function with molecular orbitals: Application to first-row molecules

TL;DR

This paper presents a new quantum chemical method combining a geminal wave function with molecular orbitals and a correlation factor, optimized via quantum Monte Carlo, to accurately describe non-dynamical correlations in molecules.

Contribution

It introduces a variational wave function approach that effectively captures non-dynamical correlations using molecular orbitals and a real space correlation factor, tested on various dimers.

Findings

Accurately reproduces non-dynamical correlations in molecules.

Effective for systems with strong non-dynamical correlations and weak van der Waals interactions.

Provides energetics and properties using quantum Monte Carlo techniques.

Abstract

We introduce a method for accurate quantum chemical calculations based on a simple variational wave function, defined by a single geminal that couples all the electrons into singlet pairs, combined with a real space correlation factor. The method uses a constrained variational optimization, based on an expansion of the geminal in terms of molecular orbitals. It is shown that the most relevant non-dynamical correlations are correctly reproduced once an appropriate number $n$ of molecular orbitals is considered. The value of $n$ is determined by requiring that, in the atomization limit, the atoms are described by Hartree-Fock Slater determinants with Jastrow correlations. The energetics, as well as other physical and chemical properties, are then given by an efficient variational approach based on standard quantum Monte Carlo techniques. We test this method on a set of homonuclear (Be2, B2, C2, N2, O2, and F2) and heteronuclear (LiF, and CN) dimers for which strong non-dynamical correlations and/or weak van der Waals interactions are present.