On the evolution of cluster to bulk properties: a theoretical LCGTO-LDF study of free and coordinated Ni_n clusters (n=6-147)

The electronic properties of Ni clusters containing up to 147 atoms have been determined by all-electron LCGTO-LDF calculations. Both icosahedral and octahedral packings have been considered, the icosahedral being always more stable than the cuboctahedral. The cohesive energy of the clusters shows a linear dependence on n^{- sol1 3}, where n is the number of atoms in the cluster; the slope of the curve is the same as for experimental cohesive energies of gas-phase Ni clusters. The first ionization potential and the electron affinity of Ni clusters qualitatively follow the prediction of the classical droplet model. The Ni clusters exhibit average magnetic moments per atom which are higher than that of metallic Ni. This enhanced magnetization is due to the presence of many low-coordinated surface atoms in the clusters. The effect of a ligand shell on the electronic structure of the Ni clusters has also been considered. He atoms have been used to simulate one of the electronic effects induced by closed shell ligands like CO, i.e. the quenching of the cluster magnetic moment. It is shown that this magnetic quenching is due to the repulsive interaction with the ligand shell and is essentially restricted to the metal atoms on the cluster surface.