High-level thermochemistry for the octasulfur ring: A converged coupled cluster perspective for a challenging second-row system

Author(s)
Karton, Amir
Publication Date
2021-12
Abstract
<p>Sulfur clusters are challenging targets for high-level ab initio procedures. The heat of formation of the most common and energetically stable S<sub>8</sub> allotrope (α-sulfur) has not been the subject of a high-level ab initio investigation. We apply the Weizmann-<i>n</i> computational thermochemistry protocols to the S<sub>8</sub> sulfur cluster. We show that calculating the heat of formation with sub-chemical accuracy requires accurate treatment of post-CCSD (T), core-valence, scalar relativistic, and zero-point vibrational energy contributions. At the relativistic, all-electron CCSDT(Q)/CBS level of theory we obtain an enthalpy of formation at 0 K of ∆<sub>f</sub><i>H</i><sup>◦</sup><sub>0</sub> = 24.44 kcal mol<sup>–1</sup>, and at 298 K of ∆<sub>f</sub><i>H</i><sup>◦</sup><sub>298</sub> = 23.51 kcal mol<sup>–1</sup>. These values suggest that the experimental values from Gurvich (∆<sub>f</sub><i>H</i><sup>◦</sup><sub>0</sub> = 25.1 ± 0.5 kcal mol<sup>–1</sup>) and JANAF (∆<sub>f</sub><i>H</i><sup>◦</sup><sub>0</sub> = 24.95 ± 0.15 and ∆<sub>f</sub><i>H</i><sup>◦</sup><sub>298</sub> = 24.00 ± 0.15 kcal mol<sup>–1</sup>) represent overestimations and should be revised downward by 0.5–0.7 kcal mol<sup>–1</sup>. We also show that computationally economical composite ab initio protocols such as G4, G4(MP2), and CBS-QB3 are unable to achieve chemical accuracy relative to our best CCSDT(Q)/CBS heat of formation for S<sub>8</sub>.</p>
Citation
Chemical Physics Impact, v.3, p. 1-5
ISSN
2667-0224
Link
Publisher
Elsevier BV
Rights
Attribution 4.0 International
Title
High-level thermochemistry for the octasulfur ring: A converged coupled cluster perspective for a challenging second-row system
Type of document
Journal Article
Entity Type
Publication

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