  We study quantum phase transitions by measuring the bond energy, the number
density, and the half-chain entanglement entropy in the one-dimensional ionic
Hubbard model. By performing the infinite density matrix renormalization group
with matrix product operator, we obtain ground states as the canonical form of
matrix product states. Depending on the chemical potential and the staggered
potential, the number density and the half-chain entanglement entropy shows
clear signatures of the Mott transition. Our results confirm the success of the
matrix product operator method for investigation of itinerant fermion systems.
