  We report on dynamical quantum transport simulations for realistic molecular
devices based on an approximate formulation of time-dependent Density
Functional Theory with open boundary conditions. The method allows for the
computation of various properties of junctions that are driven by alternating
bias voltages. Besides the ac conductance for hexene connected to gold leads
via thiol anchoring groups, we also investigate higher harmonics in the current
for a benzenedithiol device. Comparison to a classical quasi-static model
reveals that quantum effects may become important already for small ac bias and
that the full dynamical simulations exhibit a much lower number of higher
harmonics. Current rectification is also briefly discussed.
