Excitation Energies from the Entanglement Coupled Cluster Model for Doublets.

ABSTRACT: We present a spin-adapted coupled cluster singles and doubles model for the excitation energies of molecular doublets. The entanglement coupled cluster approach represents an unconventional take on the notorious problem of spin adaptation for open-shell species. In this approach, the high-spin open-shell molecular system is coupled to non-interacting bath orbitals to form a total closed-shell system. In entanglement coupled cluster theory, many of the attractive features of the spin-adapted closed-shell coupled cluster are retained: an unambiguous definition of the cluster operator and a terminating Baker-Campbell-Hausdorff expansion. The model produces excitation energies of a quality comparable to that of the closed-shell counterpart. Additionally, some ionized states that cannot be mode

SUBMITTER: Folkestad SD 

PROVIDER: S-EPMC12319896 | biostudies-literature | 2025 Jul

REPOSITORIES: biostudies-literature