The exact ground-state exchange-correlation functional of Kohn-Sham density
functional theory yields the exact transmission through an Anderson junction at
zero bias and temperature. The exact impurity charge susceptibility is used to
construct the exact exchange-correlation potential. We analyze the successes
and limitations of various types of approximations, including smooth and
discontinuous functionals of the occupation, as well as symmetry-broken
approaches.Comment: 6 pages, 5 figures, submitted to Phys. Rev.