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.