Polaron dynamics and Peierls-Nabarro barrier in a discrete molecular chain

The dynamics of an autolocalized quasiparticle in a discrete lattice is investigated analytically and numerically, taking into account the quasiparticle interaction with acoustic phonons. The dependence of the parameters of a soliton-like polaron on the carrying wave vector at large values of the latter is shown to differ from those predicted by the continuum models. We find that the saturation of the polaron velocity in a discrete system occurs below the sound velocity in the chain, a result which is in agreement with the experimental observations of the saturation of the drift velocity in some low-dimensional compounds. The potential of the Peierls-Nabarro relief caused by the lattice discreteness is calculated using perturbation theory, and pinning of a soliton by this barrier is studied numerically. For strongly localized, narrow polarons a critical value of the wave vector is needed to overcome the intersite barrier.