Ab initio potential energy surface for HeF2 in its ground electronic state

The ground state potential energy surface for He-F2 has been generated using the coupled-cluster singles and doubles excitation approach with perturbative treatment of triple excitations [CCSD(T)] and multi-reference configuration interaction (MRCI) methodologies, with augmented correlation consistent quadruple zeta basis set and diffused functions. Both the CCSD(T) and MRCI surfaces are compared and the results analyzed. The CCSD(T) surface exhibits van der Waals minima at different distances for different orientations of He approaching F2 and is adequate to describe accurately only in the region around the equilibrium bond distance of F2. The MRCI surface, on the other hand, yields reliable results for a wider range of F-F bond distances leading to the correct asymptote. Davidson correction to the MRCI surface makes it purely repulsive over the regions investigated.