INSTANTON APPROACH TO THE LATTICE POLARON PROBLEM

Starting from the path-integral approach to the process of tunneling i n the presence of phonons we develop a theoretical procedure for the c alculation of the bandwidth of the small-radius polaron in a one-dimen sional crystal lattice. A two-site analog of the Holstein molecular cr ystal model is explored to study the tunneling character in the limit of small phonon frequencies. We do not observe any changeover from the regime of Frank-Condon type of bandwidth renormalization to the so-ca lled adiabatic regime anticipated in the molecular crystal model.