A new open-shell CCSDTQ implementation and its application to the basis set convergence of post-CCSDT(Q) corrections in computational thermochemistry
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arXiv
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| Auteurs principaux: | , , |
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| Format: | Preprint |
| Publié: |
2026
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| _version_ | 1866910236543025152 |
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| author | Barman, Aditya Jones, Gregory H. Martin, Jan M. L. |
| author_facet | Barman, Aditya Jones, Gregory H. Martin, Jan M. L. |
| contents | We extend the CCSDTQ implementation in CFOUR to UHF and ROHF references and demonstrate its efficiency. We apply it to basis set convergence of post-CCSDT(Q) corrections for the W4-08 thermochemical dataset. Convergence of (Q)$_Λ$--(Q) is relatively rapid. For difficult species (e.g., B2, O3), CCSDTQ--CCSDT(Q)$_Λ$ may converge more slowly than (5)$_Λ$, but the effects and and basis-set trends oppose each other. Consequently, a single-shot CCCSDTQ(5)$_Λ$-CCSDT(Q)$_Λ$ correction appears most efficient. For radicals with bifurcating UHF solutions, energetics of the `less spin-contaminated' solution are clearly more well-behaved. Our best computed adiabatic electron affinity of ozone is in excellent agreement with experiment. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_19860 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | A new open-shell CCSDTQ implementation and its application to the basis set convergence of post-CCSDT(Q) corrections in computational thermochemistry Barman, Aditya Jones, Gregory H. Martin, Jan M. L. Chemical Physics We extend the CCSDTQ implementation in CFOUR to UHF and ROHF references and demonstrate its efficiency. We apply it to basis set convergence of post-CCSDT(Q) corrections for the W4-08 thermochemical dataset. Convergence of (Q)$_Λ$--(Q) is relatively rapid. For difficult species (e.g., B2, O3), CCSDTQ--CCSDT(Q)$_Λ$ may converge more slowly than (5)$_Λ$, but the effects and and basis-set trends oppose each other. Consequently, a single-shot CCCSDTQ(5)$_Λ$-CCSDT(Q)$_Λ$ correction appears most efficient. For radicals with bifurcating UHF solutions, energetics of the `less spin-contaminated' solution are clearly more well-behaved. Our best computed adiabatic electron affinity of ozone is in excellent agreement with experiment. |
| title | A new open-shell CCSDTQ implementation and its application to the basis set convergence of post-CCSDT(Q) corrections in computational thermochemistry |
| topic | Chemical Physics |
| url | https://arxiv.org/abs/2605.19860 |