The intercomparison of molecular force fields for triatomic molecules

A simple scheme for the intercomparison of different anharmonic force fields for the same molecule is introduced. It is based on the evaluation of quantities described as the mean absolute percentage difference (MAPD) and mean percentage difference (MPD) between two potential energy surfaces. It is applicable to any analytical form and an analytical function can be compared with a set of energy points from ab initio calculations. Minimization of the misfit can be used to fit analytical functions to a set of points or to other functions. Examples are given which illustrate the variation in the degree of coincidence shown by surfaces calculated in different ways. For two surfaces fitted to the same experimental data by different treatments the criterion that they each fit experimental observations appears to require multiple crossing of the surfaces.