The interaction energies of the dimethylsulfide-methanol (I) and dimethylthiocarbonyl-methanol (II) complexes are calculated as a function of the S.H-O distances at various levels of theory and compared to those of their oxygen analogs. At the coupled cluster level the binding energy of (I) is -5.46 kcal/mol, only slightly smaller than the hydrogen bond energy of -5.97 kcal/mol for the corresponding oxygen analog, i.e., the dimethylether-methanol complex. It is also considerably larger than for dimethylether-methylthiol, where S and O of the parent complex are interchanged. Density functional theory is unable to describe these weak interactions properly. Choosing second-order Moller-Plesset perturbation theory, the interaction potential surfaces of both complexes with respect to the three relevant intermolecular coordinates are compared. The interactions in the hydrogen bonds involving sulfur are classified by Morokuma, atoms-in-molecules, and natural bond orbital analyses. (C) 2003 American Institute of Physics.