Coupling between thermochemical contributions of subvalence correlation and of higher-order post-CCSD(T) correlation effects -- a step toward `W5 theory'
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| Format: | Preprint |
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2026
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| _version_ | 1866917411104489472 |
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| author | Barman, Aditya Jones, Gregory H. Weflen, Kaila E. Shepelenko, Margarita Martin, Jan M. L. |
| author_facet | Barman, Aditya Jones, Gregory H. Weflen, Kaila E. Shepelenko, Margarita Martin, Jan M. L. |
| contents | We consider the thermochemical impact of post-CCSD(T) contributions to the total atomization energy (TAE, the sum of all bond energies) of first- and second-row molecules, and specifically their coupling with the subvalence correlation contribution. In particular, we find large contributions from (Q) when there are several neighboring second-row atoms. Otherwise, both higher-order triples $T_3$--(T) and connected quadruples (Q) are important in systems with strong static correlation. Reoptimization of the reference geometry for core-valence correlation increases the calculated TAE across the board, most pronouncedly so for second-row compounds with neighboring second-row atoms. %just slightly increases the calculated TAE for all species, but more pronouncedly so if strong static correlation is present, as well as for second-row compounds, again especially with neighboring second-row atoms. We present a first proposal for a `W5 theory' protocol and compare computed TAEs for the W4-08 benchmark with prior reference values. For some key second-row species, the new values represent nontrivial revisions. Our predicted TAE$_0$ values (TAE at 0 K) agree well with the ATcT (active thermochemical tables) values, including for the very recent expansion of the ATcT network to boron, silicon, and sulfur compounds. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2601_02294 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Coupling between thermochemical contributions of subvalence correlation and of higher-order post-CCSD(T) correlation effects -- a step toward `W5 theory' Barman, Aditya Jones, Gregory H. Weflen, Kaila E. Shepelenko, Margarita Martin, Jan M. L. Chemical Physics We consider the thermochemical impact of post-CCSD(T) contributions to the total atomization energy (TAE, the sum of all bond energies) of first- and second-row molecules, and specifically their coupling with the subvalence correlation contribution. In particular, we find large contributions from (Q) when there are several neighboring second-row atoms. Otherwise, both higher-order triples $T_3$--(T) and connected quadruples (Q) are important in systems with strong static correlation. Reoptimization of the reference geometry for core-valence correlation increases the calculated TAE across the board, most pronouncedly so for second-row compounds with neighboring second-row atoms. %just slightly increases the calculated TAE for all species, but more pronouncedly so if strong static correlation is present, as well as for second-row compounds, again especially with neighboring second-row atoms. We present a first proposal for a `W5 theory' protocol and compare computed TAEs for the W4-08 benchmark with prior reference values. For some key second-row species, the new values represent nontrivial revisions. Our predicted TAE$_0$ values (TAE at 0 K) agree well with the ATcT (active thermochemical tables) values, including for the very recent expansion of the ATcT network to boron, silicon, and sulfur compounds. |
| title | Coupling between thermochemical contributions of subvalence correlation and of higher-order post-CCSD(T) correlation effects -- a step toward `W5 theory' |
| topic | Chemical Physics |
| url | https://arxiv.org/abs/2601.02294 |