The electronic structure of the transition metal clusters Ni1-Ni6, Cu1-Cu6, and Zn1-Zn6 is studied by ab initio SCF calculations. The configuration interaction calculations are also performed for Zn and Ni clusters. In this paper, density of the states (DOS) is discussed in detail. Using the Koopmans' theorem, we found that the d-band is completely separated from the s-band for the Cu clusters. Also, DOS given by ΔSCF with the symmetry adopted SCF calculations is parallel to that given by the Koopmans' theorem. We note that d-electrons are bound near to the nucleus compared with 4s electrons. When a d-electron is ionized, a resulting d-hole might be localized at one of the constituent atoms of the clusters. Such a model probably gives a better description for the d-electron ionization so far as the one electron approximation is employed. The calculated results for the Cu clusters meet our expectations. The resulting d-band is embedded in the 4s-band for the Cu clusters and DOS of the clusters resemble that of metal Cu. Similar results are found for the Ni and Zn clusters. It will be, however, dicussed that the Fermi level of the small clusters is somewhat larger (deeper) than that of the metals.
