This research proposes a spin-free coupled cluster method that effectively describes open-shell systems, suggesting improved calculations for complex quantum states.
Key Points
The aim is to develop a spin-free, size-extensive coupled cluster method that handles arbitrary spin eigenfunctions effectively.
Introduced a spin-free approach based on generalized normal ordered exponential ansatz.
Eliminated redundancies in excitations by selecting relevant interactions that project the reference function.
Utilized localized orbitals to ensure size-consistency in open-shell fragment dissociation.
Demonstrated competitive numerical results for prototypical multireference systems at singles and doubles levels.
The method provides more compact working equations compared to existing approaches.