Electronic structure and magnetism of Ni(100) films: Self-consistent local-orbital calculations

The electronic structure of three- and five-plane films of ferromagnetic Ni(100) has been computed self-consistently, with the use of an atomic-orbital basis. A surface-state band obtained for the five-plane film corresponds to surface-sensitive bands observed recently in angle-resolved photoemission measurements. Both films have a work function of 5.0 eV and an enhanced surface magnetization (ESM) compared with that of the inner planes, which have essentially the bulk magnetization. The contributions of dehybridization and band narrowing to ESM are assessed by repeating the calculations with $\mathrm{sp}-d$ matrix elements omitted. Also, while the occupancy of the nominal $d$ bands decreases at the surface, their $d$ character increases; cancellation of these effects explains why the $d$-orbital occupation number is nearly independent of the coordination. On the other hand, a definite surface charge transfer from $p$ to $s$ orbitals is observed in the calculations. We also studied Ni(100) monolayers with lattice spacings 10% smaller, and 20% larger, than the bulk spacing. In these systems also, the magnetization increases as the atomic limit is approached, while the number of $d$ electrons is nearly constant.