Electronic structure of small copper clusters. I

Abstract

The electronic structure of small Cu clusters Cu_n (n = 2–6) is investigated by an all‐electron SCF calculation. Basis sets for the calculations are chosen with special care. The calculated atomization energy per atom increases almost linearly with the number of the Cu atoms from Cu₄ to Cu₆, while the bond energy defined as the atomization energy per bond shows a gradual convergence. The band structure of clusters is closely investigated. The absolute value of the orbital energies for the highest occupied 4s‐like orbitals is around 5 eV for Cu₄–Cu₆, in agreement with the experimental work function (4.65 eV) of the Cu bulk; however the absolute value of the orbital energies for the highest occupied 3d‐like orbitals is around 13 eV, which is much larger than the photoelectronic result of 6.75 eV. In this connection, the importance of the reorganization effect in the d electron ionization is emphasized. It is proposed that the orbital energies of the 3d‐like orbitals should be shifted by ∼6 eV to compare them with photoelectron spectroscopic data.