A theoretical model obtained in momentum space for charge transport in a   system consisting of non-interacting polarons
  We developed a theory of charge transport in a system of non-interacting polarons. The theory was conducted to a compact relation through a nonperturbative method based on electron-phonon Hamiltonian. The derived final result represents both two different limits of band and phonon assisted transports which depends on temperature and electron-phonon coupling strength. 
F. Marsusi and J. Sabbaghzadeh
cond-mat.other