All-electron calculations were performed for Ni , Ni , and Ni clusters 2 3 4 and their respective anions and cations using density functional theory techniques as implemented in the DGauss code. Both local and generalized gradient-corrected functionals were employed. Three different multiplicities were examined for each cluster Ž . M s 3, 5, and 7 . The calculated ground states were found to have multiplicities of M s 3 for Ni and Ni and M s 5 for Ni with associated magnetic moments per atom 2 3 4 of 1.0 for Ni and Ni , while Ni shows an isotropic magnetic distribution. The B 2 4 3
cluster magnetization is enhanced relative to that of the bulk, which is in qualitative agreement with experimental data for clusters larger than 50 atoms. For these smallest Ž . Ni clusters, there is a mixture of 3d and 4 s bonding. The 3d 4 s contribution to the n Ž . bonding decreases increases going from n s 2 to n s 4, which is reflected by the larger equilibrium bond lengths of Ni , as compared to that of Ni . The frontier molecular 4 2 orbitals, the so-called HOMO and LUMO, were studied; they provide insight into the reactivity of these small particles. We also determined the lowest-energy states of anions, Ni y , and cations, Ni q . The calculated ionization potentials and electron affinities are in n n reasonable agreement with experimental observations as well as with other reported theoretical results.