The curious case of DMSO: A CCSD(T)/CBS(aQ56+d) benchmark and DFT study


This work addresses the pathological behavior of the energetics of dimethyl sulfoxide and related sulfur-containing compounds by providing the computational benchmark energetics of R2E2 species, where R = H/CH3 and E = O/S, with bent and pyramidal geometries using state-of-the-art methodologies. These 22 geometries were fully characterized with coupled-cluster with single, double, and perturbative triple excitations [CCSD(T)], second-order Møller–Plesset perturbation theory (MP2), and 22 density functional theory (DFT) methods with 8, 12, and 12, respectively, correlation consistent basis sets of double-, triple-, or quadruple-ζ quality. The relative energetics were determined at the MP2 and CCSD(T) complete basis set (CBS) limits using 17 basis sets up to sextuple-ζ and include augmented, tight-d, and core–valence correlation consistent basis sets. The relative energies of oxygen-/sulfur-containing compounds exhibit exceptionally slow convergence to the CBS limit with canonical methods as well as significant basis set dependence. CCSD(T) with quadruple-ζ basis sets can give qualitatively incorrect relative energies. Explicitly correlated MP2-F12 and CCSD(T)-F12 methods dramatically accelerate the convergence of the relative energies to the CBS limit for these problematic compounds. The F12 methods with a triple-ζ quality basis set give relative energies that deviate no more than 0.41 kcal mol−1 from the benchmark CBS limit. The correlation consistent Composite Approach (ccCA), ccCA-TM (TM for transition metals), and G3B3 deviated by no more than 2 kcal mol−1 from the benchmark CBS limits. Relative energies for oxygen-/sulfur-containing systems fully characterized with DFT are quite unreliable even with triple-ζ quality basis sets, and 13 out of 45 combinations fortuitously give a relative energy that is within 1 kcal mol−1 on average from the benchmark CCSD(T) CBS limit for these systems.

J. Chem. Phys., 155, 114304 (2021)

Errata from the author:

  • The caption to Figure 4 is wrong. The caption should denote that isomer 10 is lower in energy relative to isomer 12. Isomer 12 is higher in energy than isomer 10 at the CCSD(T) CBS limit.

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Supporting information can be found here.

Eric Van Dornshuld
Eric Van Dornshuld
Assistant Clinical Professor

My research interests include modeling small molecule systems with convergent quantum chemistry.

Charles Edwin Webster
Charles Edwin Webster
Professor and Associate Department Head

Faculty co-advisor for the MSU SMACS (2018–present).