Theoretical three-dimensional potential-energy surface for the reaction of Be with HF

The three-dimensional potential-energy surface for reaction of Be and HF has been computed and fit with an analytic form. Several hundred points on the surface were obtained from a two-configuration MC SCF function using a DZ GTO basis set. Comparisons with much larger calculations at a smalle rnumber of points suggest that this level of approximation gives a good qualitative and probably a reasonable quantitative description. The present surface is in good accord with a previous collinear surface (although the barrier is significantly higher in the present work) and also with a recently published valence-bond calculation. The surface is found to be quite insensitive to orientation for angles of approach between collinear and perpendicular: the minimum-energy path is not collinear. An analytic fit to the surface has been obtained. The general features are reproduced by a three-structure effective hamiltonian which is motivated by valence-bond-like ideas and which accurately reproduces the asymptotic diatomic limits. In the region of strong interaction this model is augmented by a damped fourth-order polynomial in the internuclear separations. Despite the complexity of this fitting function, it provides only a fair quantitative representation.