Hohenberg–Kohn theory including spin magnetism and magnetic fields

Beginning with work by U. von Barth and L. Hedin in 1972 and continuing with recent papers in 2001 by K. Capelle and G. Vignale and by H. Eschrig and W. E. Pickett, questions have been raised about the meaning and validity of Hohenberg–Kohn theory when spin magnetism and/or magnetic fields are present. This article offers clarifications of some of these questions. In particular, it also concludes that these questions do not affect spin‐density functional theory for nondegenerate ground states as currently practiced.