2024/06/13 by Arnab Bachhar, Bachhar, Arnab, Nicholas J. Mayhall +1 · 1 citation
Mathematics · Physics and Astronomy · #Chemical Physics (physics.chem-ph) #Cold Atom Physics and Bose-Einstein Condensates #FOS: Physical sciences #Random Matrices and Applications #Theoretical and Computational Physics
paper · pdf · doi:10.48550/arxiv.2406.08721
openalex publication_date 2024/06/13 · openalex created_date 2024/06/15 · openalex updated_date 2026/07/28
The cluster-based Mean Field method (cMF) and it's second order perturbative correction[1], was introduced by Jiménez-Hoyos and Scuseria to reduce the cost of modeling strongly correlated systems by dividing an active space up into small clusters, which are individually solved in the mean-field presence of each other. In that work, clusters with unpaired electrons are treated naturally, by allowing the α and β orbitals to spin polarize. While that provided significant energetic stabilization, the resulting cMF wavefunction was spin-contaminated, making it difficult to use as a reference state for spin-pure post-cMF methods. In this work, we propose the Restricted Open-shell cMF (RO-cMF) method, extending the cMF approach to systems with open-shell clusters, while not permitting spin-polarization. While the resulting RO-cMF energies are necessarily higher in energy than the unrestricted orbital cMF, the new RO-cMF provides a simple reference state for post-cMF methods that recover the missing inter-cluster correlations. We provide a detailed explanation of the method, and report demonstrative calculations of exchange coupling constants for three systems: a di-iron complex, a di-chromium complex, and a dimerized organic radical. We also report the first perturbatively corrected RO-cMF-PT2 results as well.