  To explore whether the density-functional theory non-equilibrium Green's
function formalism (DFT-NEGF) provides a rigorous framework for quantum
transport, we carried out time-dependent density functional theory (TDDFT)
calculations of the transient current through two realistic molecular devices,
a carbon chain and a benzenediol molecule inbetween two aluminum electrodes.
The TDDFT simulations for the steady state current exactly reproduce the
results of fully self-consistent DFT-NEGF calculations even beyond linear
response. In contrast, sizable differences are found with respect to an
equilibrium, non-self-consistent treatment which are related here to
differences in the Kohn-Sham and fully interacting susceptibility of the device
region. Moreover, earlier analytical conjectures on the equivalence of static
and time-dependent approaches in the low bias regime are confirmed with high
numerical precision.
