Abstract
The SX diatomics, X = first- or second-row atom, have been studied employing coupled cluster theory and the aug-cc-pV(X+d)Z basis sets. To estimate ΔfH°298, we have included a correction for core−valence (CV) correlation, spin−orbit splitting, and scalar-relativistic (SR) effects. For SO and SC, the estimated ΔfH°298 values are 0.5 kcal/mol within the experiment. However, for the remaining molecules, a revision of their ΔH°f,298 are required. Deviations as large as 10 kcal/mol have been found between our best estimates and the values adopted by the NIST-JANAF tables. The proposed ΔfH°298 (±0.5kcal/mol) are 67.6 (SB), 66.7 (SN), 0.8 (SF), 47.4 (SAl), 27.9 (SSi), 38.1 (SP), 29.4 (S2), and 27.1 (SCl) kcal/mol. For comparative purposes we performed BD(T), G3, CBS-QB3, B3LYP, and B3PW91 calculations. The mean absolute error (MAE) of the G3 and CBS-QB3 ΔfH°298 with respect to our best results is 1.0 kcal/mol for both methodologies, whereas for B3LYP/6-311+G(3df) and B3PW91/6-311+G(3df), the MAE is 1.6 and 2.0 kcal/mol, respectively. At the coupled cluster level of theory, with respect to the experiment, the MAE of the equilibrium bond lengths is 0.0013 and 0.0012 Å for the first- and second-row SX, respectively. This result involves extrapolation to the CBS limit, a correction for CV and SR effects, and also a correction for complete triple excitations. Two molecules presented an unstable HF wave function, SN and SP. In both cases, the use of the CCSDT and BD(T) methods outperformed CCSD(T). Our spin−orbit corrected coupled cluster adiabatic electron affinities (EAad) are ±0.7 kcal/mol within the experiment for SN, SO, SF, and S2. However, some discrepancies were found for SC and SAl. Our best estimates are EAad(SC) = 2.3 kcal/mol and EAad(SAl) = 62.5 kcal/mol, 2.4 and 1.6 kcal/mol larger than the experimental EAad, respectively. For SB, SSi, SP, and SCl, we propose new EAad of 53.7, 12.4, 36.5, and 59.0 kcal/mol, respectively. The MAE of the CBS-QB3 and G3 EAad with respect to our estimated EAad is 0.9 kcal/mol for both methodologies, whereas for B3LYP/6-311+G(3df) and B3PW91/6-311+G(3df), the MAE are 1.9 and 2.7 kcal/mol, respectively, but 50% of the error is provided only by SC and SN. Systematic Coupled Cluster, Brueckner Coupled Cluster, G3, CBS-QB3, and DFT Investigation of SX Diatomics; X = First- or Second-Row Atom - ResearchGate. Available from: http://www.researchgate.net/publication/231639185_Systematic_Coupled_Cluster_Brueckner_Coupled_Cluster_G3_CBS-QB3_and_DFT_Investigation_of_SX_Diatomics_X__First-_or_Second-Row_Atom [accessed Apr 16, 2015].
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