AbstractBasis set superposition error in hydrogen‐bonded systems can exaggerate attraction calculated from self‐consistent field energies as well as from electron correlation energies. One cause of this error is the basis set deficiency in describing the charge polarization of one constituent molecule when its bonding partner approaches. That constituent molecule's description is improved partly because of the proximity of the partner's basis functions, independent of real attraction. That polarization‐related error is shown to occur primarily at the SCF level and not at correlated l