We clarify some aspects of the calculation of the thermal transport coefficients. For a tight-binding Hamiltonian we discuss the approximate nature of the charge current and the thermal current obtained by Peierls substitution which is also identical to the equation of motion technique. We address the issue of choosing an appropriate basis for making the Peierls construction for transport calculations. We propose a criteria for finding an optimum Wannier basis where the difference between the exact current and the approximate one is minimum. Using the equations of motion we derive the thermal current for a generalized Hubbard model with density interaction. We identify a part which is the contribution from the long-range interactions to the heat current. For the Hubbard model we derive expressions for the transport coefficients in the limit of infinite dimensions.

• Received 1 October 2002

DOI:https://doi.org/10.1103/PhysRevB.67.115131