We present a generalized conductance formula for the multiband tight-binding model based on the formula by Caroli. We show that the transmission coefficients for Bloch states can be calculated using the expression for the self-energies of the leads in terms of the eigenstates of the secular matrix. We also show that evanescent states cannot be neglected in the calculation as is usually done. Although they do not explicitly contribute to the total conductance, they are needed to obtain the correct Green’s function and the self-energies. This formula allows for an alternative to the usual iterative method for calculating the conductance of a molecule connected to two semi-infinite leads, and can give the contributions to the conductance decomposed by conduction channel.

• Received 29 April 2002

DOI:https://doi.org/10.1103/PhysRevB.66.205319