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| Auteurs principaux: | , , |
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| Format: | Preprint |
| Publié: |
2025
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| Accès en ligne: | https://arxiv.org/abs/2504.04459 |
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| _version_ | 1866909568270860288 |
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| author | Folkestad, Sarai Dery Kruken, Kristine Lauvstad Koch, Henrik |
| author_facet | Folkestad, Sarai Dery Kruken, Kristine Lauvstad Koch, Henrik |
| contents | We present excitation energies for molecular doublets from a spin-adapted formulation of coupled cluster singles and doubles theory. 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 is retained: an unambiguous definition of the cluster operator and a terminating Baker-Campbell-Hausdorff expansion. The result is a spin-adapted coupled cluster theory for open-shell species. The model produces excitation energies of a quality comparable to the closed-shell counterpart. Additionally, some ionized states that cannot be modeled accurately with the alternative equation-of-motion approach for ionized states, can be described with the entanglement coupled cluster singles and doubles model. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_04459 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Excitation Energies from the Entanglement Coupled Cluster Model for Doublets Folkestad, Sarai Dery Kruken, Kristine Lauvstad Koch, Henrik Chemical Physics We present excitation energies for molecular doublets from a spin-adapted formulation of coupled cluster singles and doubles theory. 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 is retained: an unambiguous definition of the cluster operator and a terminating Baker-Campbell-Hausdorff expansion. The result is a spin-adapted coupled cluster theory for open-shell species. The model produces excitation energies of a quality comparable to the closed-shell counterpart. Additionally, some ionized states that cannot be modeled accurately with the alternative equation-of-motion approach for ionized states, can be described with the entanglement coupled cluster singles and doubles model. |
| title | Excitation Energies from the Entanglement Coupled Cluster Model for Doublets |
| topic | Chemical Physics |
| url | https://arxiv.org/abs/2504.04459 |