The challenge of fitting ab initio surfaces. I. Rigid-rotor CO₂---H₂ potential

Abstract

The utility of space-fixed expansion for fitting the angular dependence of the ab initio rigid-rotor CO₂---H₂ potential has been tested, using residual plots as a diagnostic tool. We find that 1D spline interpolation of the resulting radial coefficients leads to potential-energy values slightly less accurate than the 3D spline interpolation reported earlier. Our attempts to obtain a completely analytic fit (i.e. including radial as well as angular dependence) of the potential have not been successful. The implications of our results to the general problem of fitting molecule-molecule potentials are discussed.