MOLECULAR-ORBITAL STUDIES OF HYDROGEN BONDS . AN AB INITIO CALCULATION FOR DIMERIC H2O

The hydrogen-bond energy and the most stable structure of the dimeric H2O system are calculated by the LCAO MO SCF method using a medium-sized Gaussian orbital basis set. The most stable structure, found by a limited variation of the interatomic coordinates, is a linear hydrogen bond (stabilization energy 12.6 kcal mole-1) with an H⋯O distance of 1.72 Å, and with the hydrogen-acceptor molecule almost freely rotating around its molecular axis. The stretching of the proton donor O-H bond is calculated to be 0.12 Å. A population anaysis near the energy minimum shows that the change in the population is distributed not only in the O⋯H-O fragment, but also delocalized into the neighboring O-H bonds. Hydrogen bonds of dimeric H2O other than the linear structure (cyclic and bifurcated) are also examined.