Structure and binding energy of the H2S dimer at the CCSD(T) complete basis set limit

This study presents results for the binding energy and geometry of the H2S dimer which have been computed using Moller-Plesset perturbation theory (MP2, MP4) and coupled cluster (CCSD, CCSD(T)) calculations with basis sets up to aug-cc-pV5Z. Estimates of D-e, E-ZPE, D-o, and dimer geometry have been obtained at each level of theory by taking advantage of the systematic convergence behavior toward the complete basis set (CBS) limit. The CBS limit binding energy values of De are 1.91 (MP2), 1.75 (MP4), 1.41 (CCSD), and 1.69 kcal/mol (CCSD[T]). The most accurate values for the equilibrium S-S distance r(SS) (without counterpoise correction) are 4.080 (MP2/aug-cc-pV5Z), 4.131 (MP4/aug-cc-pVQZ), 4.225 (CCSD/aug-cc-pVQZ), and 4.146 angstrom (CCSD(T)/aug-cc-pVQZ). This study also evaluates the effect of counterpoise correction on the H2S dimer geometry and binding energy. As regards the structure of (H2S) 2, MPn, CCSD, and CCSD(T) level values of rSS, obtained by performing geometry optimizations on the counterpoisecorrected potential energy surface, converge systematically to CBS limit values of 4.099 (MP2), 4.146 (MP4), 4.233 (CCSD), and 4.167 angstrom (CCSD(T)). The corresponding CBS limit values of the equilibrium binding energy D-e are 1.88 (MP2), 1.76 (MP4), 1.41 (CCSD), and 1.69 kcal/mol (CCSD(T)), the latter in excellent agreement with the measured binding energy value of 1.68 +/- 0.02 kcal/mol reported by Ciaffoni et al. [Appl. Phys. B92, 627 (2008)]. Combining CBS electronic binding energies D-e with EZPE predicted by CCSD(T) vibrational second-order perturbation theory calculations yields D-o = 1.08 kcal/mol, which is around 0.6 kcal/mol smaller than the measured value of 1.7 +/- 0.3 kcal/mol. Overall, the results presented here demonstrate that the application of high level calculations, in particular CCSD(T), in combination with augmented correlation consistent basis sets provides valuable insight into the structure and energetics of the hydrogen sulfide dimer. Published by AIP Publishing.