Two-channel conduction through polyacenes-Extension of the source-sink potential method to multichannel coupling to leads

The source and sink potential method of Goyer et al. [J. Chem. Phys. 126, 144104 (2007)] is extended to the case of multichannel coupling to leads. The formulation leads to a nonlinear equation for just one (the elastic) reflection coefficient. Solution of this equation, in general, requires repeated computation of an n x n determinant, where n is the number of supermolecule basis functions directly coupled to the source lead, as opposed to a determinant with order equal to the full size of supermolecule basis. The method is applied to a Huckel model of two-channel polyacene conduction. A simple model of resonance lineshapes is developed in case of weak coupling to leads. The model accurately relates peak characteristics to orbital probabilities associated with the eigenvectors of the isolated molecule Hamiltonian. The model shows how orbital probabilities that give rise to transmission resonances (i.e., 100% transmission), in the case of single-channel conduction, give rise to equal probabilities (of 1/4) for the two reflections and two transmissions, in the case of two-channel conduction. The model also shows how splitting of degenerate eigenvalues of the isolated molecule Hamiltonian results in overlapping resonances characterized by a single complex lineshape. (C) 2011 American Institute of Physics. [doi:10.1063/1.3535117]