The electronic structure and magnetic properties of small Ni-n clusters (n = 4, 5, 6, 8, 13) are studied at the self-consistent-field multireference configuration interaction singles level using the intermediate neglect of differential overlap model Hamiltonian parametrized for spectroscopy. Results are in agreement with density functional theory calculations and ab initio calculations for the smaller (n = 4-6) structures, Discrepancies develop for the larger (n = 8, 13) structures, and these discrepancies are discussed. We examine systems and criteria for the selection of the cluster size that most accurately model heterogeneous catalysts.