We describe a simple method to automate the geometric optimization of molecular orbital calculations of supermolecules on potential surfaces that are corrected for basis set superposition error using the counterpoise ͑CP͒ method. This method is applied to the H-bonding complexes HF/HCN, HF/H 2 O, and HCCH/H 2 O using the 6-31G͑d,p͒ and D95ϩϩ͑d,p͒ basis sets at both the Hartree-Fock and second-order Mo "ller-Plesset levels. We report the interaction energies, geometries, and vibrational frequencies of these complexes on the CP-optimized surfaces; and compare them with similar values calculated using traditional methods, including the ͑more traditional͒ single point CP correction. Upon optimization on the CP-corrected surface, the interaction energies become more negative ͑before vibrational corrections͒ and the H-bonding stretching vibrations decrease in all cases. The extent of the effects vary from extremely small to quite large depending on the complex and the calculational method. The relative magnitudes of the vibrational corrections cannot be predicted from the H-bond stretching frequencies alone.

A novel definition for the hydrogen bond is recommended here. It takes into account the theoretical and experimental knowledge acquired over the past century. This definition insists on some evidence. Six criteria are listed that could be used as evidence for the presence of a hydrogen bond.