  We calculate the exact Kohn-Sham (KS) scalar and vector potentials that
reproduce, within current-density functional theory, the steady-state density
and current density corresponding to an electron quasiparticle added to the
ground state of a model quantum wire. Our results show that, even in the
absence of an external magnetic field, a KS description of a steady-state
system in general requires a non-zero exchange-correlation magnetic field that
is purely mechanical in origin. The KS paramagnetic current density is not, in
general, that of the interacting system in any gauge.
