Optical absorption and activated transport in polaronic systems
  We present exact results for the optical response in the one-dimensional Holstein model. In particular, by means of a refined kernel polynomial method, we calculate the ac and dc electrical conductivities at finite temperatures for a wide parameter range of electron phonon interaction. We analyze the deviations from the results of standard small polaron theory in the intermediate coupling regime and discuss non-adiabaticity effects in detail. 
G. Schubert, G. Wellein, A. Wei{\ss}e, A. Alvermann, and H. Fehske