Modeling hydrogen bonds in three dimensions

The effective potential between two hydrogen bonded atoms is calculated on the basis of the Lippencott-Schroeder bent bond model, taken to be a typical model interaction. We differ from other calculations in that the minimum energy configuration for the proton is treated adiabatically, its position being recomputed at each value of the larger atoms separation. We find the typical hard core to have been a consequence of an artificial restriction of the proton to a fixed angle with the larger atom axis, basically a one-dimensional assumption. Free to move in three dimensions, the proton is squeezed off the axis as the separation narrows, and the hard core feature is gone. Depending on the degree of bond bending, the anharmonicity of the bond may be diminished, eliminated, or even reversed.