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arXiv · 2307.14694

Post-CCSD(T) corrections to bond distances and vibrational frequencies: the power of $Λ$

Maciej Spiegel·Emmanouil Semidalas·Jan M. L. Martin·Megan R. Bentley·John F. Stanton
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Abstract

The importance of post-CCSD(T) corrections as high as CCSDTQ56 for ground-state spectroscopic constants ($D_e$, $ω_e$, $ω_ex_e$, and $α_e$) has been surveyed for a sample of two dozen mostly heavy-atom diatomics spanning a broad range of static correlation strength. While CCSD(T) is known to be an unusually felicitous `Pauling point' between accuracy and computational cost, performance leaves something to be desired for molecules with strong static correlation. We find CCSDT(Q)$_Λ$ to be the next `sweet spot' up, of comparable or superior quality to the much more expensive CCSDTQ. A similar comparison applies to CCSDTQ(5)$_Λ$ vs. CCSDTQ5, while CCSDTQ5(6)$_Λ$ is essentially indistinguishable from CCSDTQ56. A composite of CCSD(T)-X2C/ACV5Z-X2C with [CCSDT(Q)$_Λ$ -- CCSD(T)]/cc-pVTZ or even cc-pVDZ basis sets appears highly effective for computational vibrational spectroscopy. Unlike CCSDT(Q) which breaks down for the ozone vibrational frequencies, CCSDT(Q)$_Λ$ handles them gracefully.

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Maciej Spiegel, Emmanouil Semidalas, Jan M. L. Martin, Megan R. Bentley, John F. Stanton. 2023-08-22. Post-CCSD(T) corrections to bond distances and vibrational frequencies: the power of $Λ$. https://doi.org/10.1080/00268976.2023.2252114

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