Siberian Federal University

The effects of strong electron-phonon interaction in a realistic model of a system with strong Coulomb correlations are analyzed using the Lang and Firsov transformation. It is shown that polaronic and bipolaronic transformations, widely discussed in the literature and associated with a smooth or sharp transitions in the properties of charge carriers when the strength of the electron-phonon coupling changes, determine the switching of the system between the regimes of correlated carriers, polarons or bipolarons. These transitions are controlled by the local electron-phonon interaction of the Holstein type. At the same time, the non local electron-lattice contribution associated with the modulation of the hopping integral plays a major role in the crossover of the polaron and bipolaron regimes in the limit of strong electron correlations