and dimers of mixed-influence interactions, where neither of these conditions is met. It is useful to group the complexes in this way because the hydrogen-bonded subset (containing 23 dimers involving water, methanol, acetic acid, and other polar monomers) places stringent demands on the basis set as compared to the other S66 systems. The dispersion-bound subset contains 23 dimers involving monomers such as benzene, pyridine, and ethylene.