Electron correlation effects at the Gd„0001... surface

We have performed full-potential linearized augmented plane wave calculations of the Gd~0001! surface using the local density approximation ~LDA! together with the Hubbard U ~LDA1U! total energy functional. The use of LDA1U instead of LDA total energy calculations leads to a ferromagnetic ground state for both bulk Gd and the Gd surface, in agreement with experimental observation. The calculated downward shift of 4 f eigenvalues for the Gd surface is in agreement with experimentally observed binding energies. Surface strain relaxation leads to a 90% enhancement of the interlayer surface-to-bulk effective exchange coupling. Application of a Landau–Ginzburg-type theory yields a 30% enhancement of the Curie temperature at the surface, in very good agreement with the experiment. © 2000 American Institute of Physics. @S0021-8979~00!50208-4#