New aspect of hydrogen sulfide dimer: CCSD(T)/CBS potential surface of antiparallel interactions

The potential energy surface of the hydrogen sulfide dimer with antiparallel S–H⋯H–S orientations was investigated by high-level very accurate CCSD(T)/CBS quantum chemical calculations. More than 1300 geometries were calculated to characterize the potential energy surface. The antiparallel dimer that is minimum on the potential surface has an interaction energy of −1.57 kcal/mol, only slightly less strong than that of the classical hydrogen-bonded dimer (−1.71 kcal/mol). These data demonstrate that antiparallel interaction represents an important stabilization motif in hydrogen sulfide aggregates. Symmetry-adapted perturbation theory reveals that the interaction is governed by comparable electrostatic (47%) and dispersion (43%) contributions, in contrast to the antiparallel water dimer, where electrostatic interactions dominate. The present study provides the first detailed characterization of the antiparallel interaction in the hydrogen sulfide dimer and extends the understanding of the shallow potential energy surface of this system.