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Updated: Jul 26, 2025

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
Published on: April 8, 2020
Entanglement coupled cluster theory: Exact spin-adaptation
Sarai Dery Folkestad1, Bendik Støa Sannes1, Henrik Koch1,2
1Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim, Norway.
Abstract:
We present a novel framework for spin-adapted coupled cluster theory. The approach exploits the entanglement of an open-shell molecule with electrons in a non-interacting bath. Together, the molecule and the bath form a closed-shell system, and electron correlation can be included using the standard spin-adapted closed-shell coupled cluster formalism. A projection operator, which enforces conditions on the electrons in the bath, is used to obtain the desired state of the molecule. This entanglement coupled cluster theory is outlined, and proof-of-concept calculations for doublet states are reported. The approach is further extendable to open-shell systems with other values of the total spin.
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