Morphing ab initio potentials: A systematic study of Ne–HF

A procedure for “morphing” an ab initio potential energy surface to obtain agreement with experimental data is presented. The method involves scaling functions for both the energy and the intermolecular distance. In the present work, the scaling functions are parametrized and determined by least-squares fitting to the experimental data. The method is tested on the system Ne–HF, for which high-resolution infrared spectra are available. It is shown to work well even with relatively low-level ab initio calculations. Several basis sets are investigated at the CCSD(T) correlation level, including various aug-cc-pVnZ basis sets and the specially-tailored Ne–HF basis set of ONeil et al. All give good results after morphing, but the changes needed to match experiment are much smaller for the ONeil basis set. The use of MP2 calculations is also investigated: again, the MP2 potential is quite satisfactory after morphing, but requires much more modification than the CCSD(T) potential.