We consider the influence of a nearest-neighbor Coulomb interaction in an extended Hubbard model and introduce a new interaction term which simulates atomic polarizabilities. This has the effect of screening the on-site Coulomb interaction for charged excitations, unlike a neighbor Coulomb interaction which reduces energies of locally neutral excitations. We find that the spin density to charge density wave phase transition, however, is determined by the unscreened on-site Coulomb repulsion. The order of this phase transition is affected by polarization. We show that new phases appear, one of which is ferroelectric, when atomic polarizabilities are explicitly included.
van de Brink, J., Meinders, M. B. J., Lorenzana, J., Eder, R., & Sawatzky, G. A. (1995). New phases in an extended Hubbard model explicitly including atomic polarizabilities. Physical Review Letters, 75(25), 4658-4661. https://doi.org/10.1103/PhysRevLett.75.4658