By direct-fitting the parameters in the physically motivated extended Hartree-Fock approximate correlation energy model to spectroscopic data, potential curves have been obtained for a variety of diatomic systems that mimic the ro-vibrational data often within much less than 1 cm(-1), The approach offers a simple, yet accurate, scheme for modeling the two-body terms that are the leading contributions in a cluster expansion of potential energy surfaces of larger dimensionality. (c) 2006 Elsevier B.V. All rights reserved.