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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.
We developed a new entanglement coupled cluster theory for open-shell molecules. This method uses a non-interacting electron bath to simplify calculations, enabling accurate electron correlation analysis.
Area of Science:
- Quantum Chemistry
- Theoretical Chemistry
- Computational Chemistry
Background:
- Open-shell molecules present challenges in accurately calculating electron correlation.
- Standard coupled cluster methods are typically designed for closed-shell systems.
Purpose of the Study:
- To introduce a novel spin-adapted coupled cluster framework for open-shell systems.
- To leverage entanglement with a non-interacting bath to simplify calculations.
Main Methods:
- Developed a theoretical framework exploiting molecule-bath entanglement.
- Treated the combined molecule-bath system as closed-shell.
- Employed a projection operator to isolate the molecular state.
Main Results:
- Successfully outlined the entanglement coupled cluster theory.
- Performed proof-of-concept calculations for doublet states.
- Demonstrated the framework's applicability to various spin states.
Conclusions:
- The entanglement coupled cluster theory provides a viable approach for open-shell systems.
- The method is extendable to systems with different total spin values.
- This framework enhances the study of electron correlation in open-shell molecules.
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