An analytical six‐dimensional potential energy surface for (HF)2 from ab initio calculations

We have developed an analytical expression for the 6D potential energy surface of (HF)2 and fitted it to 1061 ab initio points covering an energy range of up to 25 000 cm−1 above equilibrium. The ab initio calculation used the coupled pair functional approach with an extended polarized basis set. We have adjusted 42 parameters (and constrained 7 others) in the fitting of the analytical function to the points; the standard deviation of the weighted fitting is 26.8 cm−1 . The minimum energy path from the linear saddle point (345 cm−1 above equilibrium), through the equilibrium point, to the C2h saddle point (332 cm−1 above equilibrium) has been determined, and several cuts through the potential are presented. We plan to use this potential surface in reaction path and close coupling calculations of rotation–vibration term values.