  We investigate the ground-state phase diagram of the one-dimensional
half-filled Hubbard model with an alternating potential--a model for the
charge-transfer organic materials and the ferroelectric perovskites. We
numerically determine the global phase diagram of this model using the
level-crossing and the phenomenological renormalization-group methods based on
the exact diagonalization calculations. Our results support the mechanism of
the double phase transitions between Mott and a band insulators pointed out by
Fabrizio, Gogolin, and Nersesyan [Phys. Rev. Lett. 83, 2014 (1999)]: We confirm
the existence of the spontaneously dimerized phase as an intermediate state.
Further we provide numerical evidences to check the criticalities on the phase
boundaries. Especially, we perform the finite-size-scaling analysis of the
excitation gap to show the two-dimensional Ising transition in the charge part.
On the other hand, we confirm that the dimerized phase survives in the
strong-coupling limit, which is one of the resultants of competition between
the ionicity and correlation effects.
