Coupled cluster theory for multireference and open-shell molecules

Abstract:We introduce a simple coupled cluster approach for multireference and open-shell systems. In the restricted active space coupled cluster framework, the cluster operator only includes excitations from doubly occupied to virtual orbitals, and this ensures the individual operators commute among each other. The ground and excited states are obtained by diagonalisation of the coupled cluster similarity transformed Hamiltonian in a restricted active space. We demonstrate the framework for the RAS-CCSD model, where single and double excitations are included in the cluster operator, and likewise for a complete active space. We consider systems with multireference character and open-shell systems in a spin-adapted manner. The approach captures significantly more dynamical correlation than without the coupled cluster similarity transformation.

Chemical Physics (physics.chem-ph); Quantum Physics (quant-ph)

arXiv:2610.07440 [physics.chem-ph]

(or arXiv:2610.07440v1 [physics.chem-ph] for this version)

https://doi.org/10.48550/arXiv.2610.07440 Focus to learn more arXiv-issued DOI via DataCite (pending registration)

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