DFT study of the structural and electronic properties of small Ni-n (n=2-4) clusters

All-electron calculations were performed for Ni-2, Ni-3, and Ni-4 clusters and their respective anions and cations using density functional theory tec hniques as implemented in the DGauss code. Both local and generalized gradi ent-corrected functionals were employed. Three different multiplicities wer e examined for each cluster (M = 3, 5, and 7). The calculated ground states were found to have multiplicities of M = 3 for Ni-2: and Ni-3 and M = 5 fo r Ni-4 with associated magnetic moments per atom of 1.0 mu(B) for Ni-2 and Ni-4, while Ni-3 shows an isotropic magnetic distribution. The cluster magn etization is enhanced relative to that of the bulk, which is in qualitative agreement with experimental data for clusters larger than 50 atoms. For th ese smallest Ni, clusters, there is a mixture of 3d and 4s bonding. The 3d( 4s) contribution to the bonding decreases (increases) going from n = 2 to n = 4, which is reflected by the larger equilibrium bond lengths of Ni-4, as compared to that of Ni-2. The frontier molecular orbitals, the so-called H OMO and LUMO, were studied; they provide insight into the reactivity of the se small particles. We also determined the lowest-energy states of anions, Ni-n(-), and cations, Ni-n(+). The calculated ionization potentials and ele ctron affinities are in reasonable agreement with experimental observations as well as with other reported theoretical results. (C) 1999 John Wiley & Sons, Inc.