Charging effects, forces, and conduction in molecular wire systems.

Recently, experiments have shown that effects arising from charging and conformational changes in a molecular wire due to an applied voltage bias can have a significant influence on the transport characteristics of the system. We introduce a tractable theoretical approach based on Landauer theory and total energy methods that treats transport nonlinearities, conformational changes, and charging effects in molecular wires in a unified way. We apply this approach to molecular wires consisting of short chain molecules with different electronic and structural properties bonded to metal contacts. We find that the nonlinear conductance characteristics of these systems are remarkably similar and can be understood in terms of a single physical mechanism. We predict that negative differential resistance should occur at high bias in such molecular wires due to the combined effects of charging and conformational changes on their electronic structure.