One-dimensional ionic Hubbard model in the high ionicity limit

We consider a Hubbard chain with an energy difference Delta between the odd and even sites. The model, known as the one-dimensional ionic Hubbard model, is used to describe the neutral-ionic transition in mixed-stack charge-transfer organic crystals and the displacive-type ferroelectric transition in perovskite oxide compounds. We show that for sufficiently large Delta and electron densities less than half-filling the system reduces to the one-band Hubbard model with a bond-site interaction, model known as relevant to quasi-one-dimensional materials with a large conduction bandwidth.