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

The dynamics of an autolocalized quasiparticle in a discrete lattice is inv estigated analytically and numerically, taking into account the quasipartic le interaction with acoustic phonons. The dependence of the parameters of a soliton-like polaron on the carrying wave vector at large values of the la tter is shown to differ from those predicted by the continuum models. We fi nd 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 so me low-dimensional compounds. The potential of the Peierls-Nabarro relief c aused by the lattice discreteness is calculated using perturbation theory, and pinning of a soliton by this barrier is studied numerically. For strong ly localized, narrow polarons a critical value of the wave vector is needed to overcome the intersite barrier. (C) 2000 Elsevier Science S.A. All righ ts reserved.