ELECTRONIC AND ATOMIC-STRUCTURE OF COPPER CLUSTERS

The electronic and geometrical structure of Cu microclusters is invest igated utilizing a parametrized tight-binding linear-muffin-tin-orbita l (TB-LMTO) method in combination with the real-space recursion techni que. The parameters of the TB-LMTO Hamiltonian are derived from ab ini tio self-consistent k-space TB-LMTO calculations for the corresponding cluster material in its bulk phase for varying lattice constants. It is found that Cu clusters exhibit certain similarities to simple-metal clusters with respect to the gross electronic features: The calculate d density-of-state (DOS) spectra exhibit exceptionally large gaps for sizes corresponding to the well-known magic numbers of the spherica je llium model. Likewise, this shell structure shows up as pronounced dro ps at the magic sizes in calculated ionization potentials, in agreemen t with recently published experimental data. For the geometrical struc ture of Cu clusters we find high-symmetry arrangements to be Jahn-Tell er unstable. The geometry of the magic Cu20 cluster, obtained by means of the simulated annealing strategy, exhibits a high sphericity, but low overall symmetry. The calculated root-mean-square bond-length fluc tuation in Cu20 qualitatively matches the results from molecular dynam ics simulations for other materials. Due to the dramatically growing c omputational difficulties with increasing cluster size, for larger clu sters with sizes N > 55, only uniformly relaxed fcc structures were ex amined. For such geometries, the DOS spectra in the range N almost-equ al-to 500 are found to be almost fully converged to the corresponding k-space result of solid Cu.