Band magnetism in the spin-density-functional formalism

Abstract

A band model of magnetism is obtained from the Hohenberg‐Kohn‐Sham spin‐density‐functional (SDF) formalism. The equations of this scheme have the simple independent particle form, and correlation effects are included via an effective potential. Usually, this potential is calculated in the local‐spin‐density (LSD) approximation. This approximation is discussed and reasons for its success are shown. Its accuracy is illustrated by a few applications related to magnetism. The independent particle form of the SDF equations can be used to derive a first principles Stoner model. Results for transition metals obtained using this model as well as using band calculational methods are reviewed. The LSD‐Stoner model gives far too high results for the Curie temperature T_c. The reason is probably the neglect of spin fluctuations above T_c in this model. In a calculation for iron dimer it is shown that there is a strong tendency to form local moments in the LSD approximation. The Heisenberg type coupling constant between the moments is discussed. The calculation suggests that spin fluctuations are important.