The thermoelectric properties of the small polaron

The high temperature behaviour of the thermoelectric transport coefficients for the Holstein small polaron model is investigated. An expression for the energy flux operator is derived, which includes the flow of the electron-lattice interaction energy. This inclusion is necessary for the small polaron model, because the electron-phonon coupling is assumed to be strong, while the kinetic energy of the electrons is understood as a small perturbation. Kubo formulae are used and approximated in lowest order perturbation theory. It follows that there are no dynamical corrections to the thermoelectric power. But the strong electron-lattice interaction leads to a contribution to the thermal conductivity.