Theoretical Calculations of Hydrogen-Bond Geometries

Abstract

The calculation of reliable hydrogen-bond geometries is more difficult than for covalent bond geometries. One obvious reason for this is that the simplest relevant systems are necessarily more complex since they involve dimers, trimers, and higher polymers, instead of monomers. A second reason is that the weaker attractive forces which attenuate more slowly result in a potential energy surface near the minimum, which is much shallower than for covalent bonds. Consequently, relatively small changes in energy correspond to relatively large changes in bond lengths and bond angles. Since all methods seek the energy minimum, a higher accuracy of calculation is necessary to obtain the same accuracy in hydrogen-bond lengths and angles than can be obtained with a covalently bonded system of the same complexity.