BULK AND SURFACE MAGNETISM AND INTERPLANAR SPACINGS IN GD FROM FIRST-PRINCIPLES CALCULATIONS

The magnetic ground state of bulk Gd and surface Gd is investigated by means of first-principles calculations based on the local-spin-densit y approximation. Good agreement between theory and experiment is found for all calculated bulk properties only if we treat the 4f states as core electrons. For the bulk calculations we also studied the effect o f the generalized gradient correction to the potential, and also good agreement between theory and experiment was found only when we treated the 4f states as core electrons. At compressed volumes we predict tha t bulk Gd should become antiferromagnetic. Our calculations reproduce the experimentally determined, ferromagnetic alignment between the sur face and subsurface layers of Gd (0001), as well as a similar to 0.13 Angstrom inward relaxation of the surface layer.