  The ionic Hubbard model is investigated at half filling at zero temperature.
We apply the cellular dynamical mean-field theory to the one-dimensional ionic
Hubbard model to compute local quantities such as double occupancy and
staggered charge density. Both quantities provide general transition behavior
of the model from a band insulating phase to a Mott insulating phase. The
renormalized band gap is introduced as an efficient order parameter for the
transition from a band insulator. We also present the spectral properties of
the ionic Hubbard model, which exhibit characteristic features for both weak
and strong interactions.
