2025/07/17 by Nicholas C.J. Lee, David P. Tew, Lee, Nicholas +1 · 1 citation
Chemistry · Materials Science · Physics and Astronomy · #Advanced Chemical Physics Studies #Advanced Physical and Chemical Molecular Interactions #Chemical Physics (physics.chem-ph) #FOS: Physical sciences #Magnetism in coordination complexes
paper · pdf · doi:10.48550/arxiv.2507.13472
openalex publication_date 2025/07/17 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We present a spin-free, size-extensive, and size-consistent coupled cluster method based on a generalised normal ordered exponential ansatz. This approach is a natural generalisation of single-reference coupled cluster theory for arbitrary spin eigenfunctions. The working equations are size-extensive through the generalised normal order formalism, and made spin-free with the spin-ensemble approach. Redundancies amongst excitations are eliminated by selecting only those excitations that project the reference function onto the first-order interacting space. Furthermore, by utilising localised orbitals, the proposed method describes dissociation into open-shell fragments size-consistently. Numerical results on prototypical multireference systems at the singles and doubles level of theory are competitive with existing multireference approaches, yet with more compact working equations.