Singlet Geminal Wavefunctions

TL;DR

This paper introduces singlet geminal wavefunctions that explicitly couple electron pairs to better describe open-shell systems and transition metal chemistry, showing improved results over traditional closed-shell approaches.

Contribution

It develops a new class of geminal wavefunctions explicitly designed for open-shell singlet states, extending the applicability of pair-based wavefunctions.

Findings

Numerical results show improved accuracy over closed-shell methods.

Explicit coupling of second-quantized operators enhances wavefunction flexibility.

Applicable to systems with nonzero spin and transition metals.

Abstract

Wavefunction forms based on products of electron pairs are usually constructed as closed-shell singlets, which is insufficient when the molecular state has a nonzero spin or when the chemistry is determined by $d$- or $f-$electrons. A set of two-electron forms are considered as explicit couplings of second-quantized operators to open-shell singlets. Geminal wavefunctions are constructed and their structure is elaborated. Numerical results for small model systems clearly demonstrate improvement over closed-shell singlet pairs.