Unified phase diagram of models exhibiting a neutral-ionic transition

We have studied the neutral-ionic transition in organic mixed-stack compounds. A unified model has been derived which, in limiting cases, is equivalent to the models proposed earlier, the donor-acceptor model, and the ionic Hubbard model. Detailed numerical calculations have been performed on this unified model with the help of the density-matrix renormalization-group (DMRG) procedure calculating excitation gaps, ionicity, lattice site entropy, two-site entropy, and the dimer order parameter on long chains and the unified phase diagram has been determined.