My effort concentrated on the bond, angle, and dihedral force constants. The non-bond interaction parameters from Bruce Gelin's thesis were used without modification or cutoffs for the model systems. These nonbond parameters are the same as those found in PARMFIX10.
The hydrogen bond geometries and well depths were obtained from a table of typical values found in Vinogradov and Linell. Because the van der Waals and electrostatic terms contribute significantly to the total hydrogen bond energy, the hydrogen bond parameters were adjusted to give an energy minimized water dimer with the desired geometry and well depth. The other terms were shifted similarly, although by smaller amounts because the van der Waals interaction is not as large in the longer nitrogen-oxygen and nitrogen-nitrogen pairs. No hydrogen bonds were present in the model systems used above.