Perturbative approach to orbital magnetism in density-functional theory

It is shown how to calculate the total energy, the single-particle energies, and the current density of an interacting current-carrying many-body system, from solutions of the Kohn-Sham equation of conventional density-functional theory. On the conceptual side, this procedure, which applies both in the presence and absence of external magnetic fields, sheds light on the role of orbital magnetism in density-functional theory and the interrelation of conventional and current-density functional theory. On the practical side it provides a computationally simple many-body approach to the interplay of orbital magnetism and electron-electron interactions in atoms, molecules, and solids.