Tight binding description of the electronic response of a molecular deviceto an applied voltage

We analyze the effect of an external electric field on the electronic struc ture of molecules which have been recently studied as molecular wires or di odes. We use a self-consistent tight binding technique that provides result s in good agreement with ah initio calculations and that may be applied to a large number of molecules The voltage dependence of the molecular levels is mainly linear with slopes intimately related to the electronic structure of the molecules. We emphasize that the response to the applied voltage is an important feature that governs the behavior of a molecular device.