BANDSTRUCTURE AND LOCALIZED DESCRIPTIONS OF NARROW-BAND SYSTEMS

In this note I would like to give some personal views on the relevance of bandstructure treatments of narrow-band systems. At first sight one might think that bandstructure theory is not a very appropriate framework for quasi-localized electrons. Nevertheless, it has been found that density-functional (DF) theory in its modern form gives a rather impressive description of ground-state properties for the majority of systems, not only " in principle " but also in practice via calculations based on the local-density approximation (LDA). I will here discuss some key concepts in DF theory with emphasis on physical significance of the eigenvalues which appear in the DF one-electron-like equations. I will also to some extent discuss the dynamical selfenergy Σ, which describes the " one-electron " excitations reached by adding or removing an electron, although there is very little work done for narrow-band electrons.