A conformational study of the influence of vibrations on conduction in molecular wires

We present two examples of the influence of vibrations on electronic transport in molecular wires. Conductance is computed using a scattering approach and the effect of vibrations is included in a static picture where the conductance is computed for a sample of nuclear geometries. The physical picture involved is that of electrons tunneling elastically through variable geometries, and is a first approach to the real problem of inelastic scattering and dynamical electron-phonon coupling. The first example corresponds to a one-dimensional tight-binding model wire, where we study changes in conduction as a consequence of dimerization and soliton formation. In the second example, we consider a more realistic wire, a p-benzene-dithiol molecule, described with an extended Huckel Hamiltonian. We calculate the conductance for different distorted geometries obtained by taking displacements along the normal modes. For the tight-binding wire, we obtain important changes in the linear current depending on the location of the soliton deformation and the magnitude of dimerization. The effect is traced back to the strong influence geometry has on the electronic structure of the wire, whose overlap with the leads determines the current. For the p-benzene-dithiol case, we find a weak dependence of the effective coupling on the nature of the vibrational mode.