title: N-representability in noncollinear spin-polarized density-functional theory.
abstract: The N-representability problem for noncollinear spin-polarized densities was left open in the pioneering work of von Barth and Hedin [J. Phys. C 5, 1629 (1972)] setting up the Kohn-Sham density-functional theory for magnetic compounds. In this Letter, we demonstrate that, contrarily to the nonpolarized case, the sets of pure and mixed state N-representable densities are different in general. We provide a simple characterization of the latter by means of easily checkable necessary and sufficient conditions on the components ρ(αβ)(r) of the spin-polarized density.
authors.affiliation: Université Paris Est, CERMICS (ENPC), INRIA, F-77455 Marne-la-Vallée, France.
authors.forename: David
authors.initials: D
authors.lastname: Gontier