On the metallic behavior of Co clusters

The role of structure in the nonmetal-metal transition of Co clusters is in vestigated by performing calculations for different symmetries: hexahedral, octahedral and decahedral. This transition occurs when the density of stat es at the Fermi level exceeds 1/k(B)T and the discrete energy levels begin to form a quasi-continuous band. The electronic structure is calculated inc luding spd orbitals and spillover effects in a Hubbard Hamiltonian solved w ithin the unrestricted Hartree-Fock approximation. We find that in small cl usters (N less than or equal to 40) the metallic behavior is strongly relat ed to the geometrical structure of the cluster. We compare our results with those coming out of a simple Friedel's model. (C) 1999 Elsevier Science Lt d. All rights reserved.