On the calculation of atomic spin densities of hcp surface clusters of transition metals (Co, Ni, Cu), of medium size (100–1000 atoms)

In the present work it is proposed a very general quantum theoretical approach, able to describe the electronic structure of big molecular systems, that have a large number of unpaired electrons. The feasibility of the method is established by calculating, at semi-empirical level, the (restricted) atomic spin densities of 90 hcp surface clusters, in the range 20–1000 atoms, for the Co, Ni, Cu metals. Agreement of atomic magnetizations (spin moments) with, both, the Stern–Gerlach magnetic deflection, and the magnetic circular dichroism experimental ones, is achieved. A better theoretical description, according to these experimental results, is provided for the surface of the Ni metal. Finally, it is found that there exists a small excess of electronic density in the surface of these metals.