Spin-polarized electronic structure of the Ni(001) surface and thin films

Spin-polarized energy bands, charge and spin densities have been calculated self-consistently for one, three, and five atomic (001) layers of fcc Ni using the linear augmented plane-wave method and the von Barth—Hedin approximation for exchange and correlation. The self-consistent potential of the five-layer film is used to calculate the electronic structure of a 13-layer film. The theoretical work function of 5.4 eV agrees well with the experimental value of 5.2 eV. The calculated spin moments are ordered ferromagnetically in all the films considered, and the moments of the atoms in the surface layer are 0.95, 0.69, and 0.65 Bohr magnetons for the one-, three-, and five-layer films, respectively. The moment of an atom in the central layer of the five-layer film is 0.61 Bohr magnetons as compared with the calculated (experimental) bulk value of 0.59±0.01 (0.56) Bohr magnetons. The increase of the magnetic moment at the surface is mainly of $d(x^2-y^2)$ character. The calculated $4s$ contribution to the hyperfine field changes sign and becomes positive in the outermost layer. Near $k=0\mathrm{}$, between the Fermi level and the $d$-band edge (which lies 0.3 eV below the Fermi level), we find no majority-spin surface states that can explain the sign reversal of the electron spin polarization near threshold. This supports the suggestion by Liebsch that, in photoemission experiments on Ni, correlation effects make the majority-spin bands appear higher in energy. With such an adjustment of our energy bands we are able to identify the two spin-up $\overline{\Sigma }$ surface bands, but not the ${\overline{\Delta }}_1$ band, observed in angular-resolved photoemission experiments.