where T junc and k B are, respectively, the junction temperature and the Boltzmann constant. φ b varies linearly along x from φ b to φ b + eV (Fig. ), therefore, at zero bias voltage the trapezoidal barrier reduces to a rectangular barrier of constant height, φ b . We note that Eqns. 2-5 can describe coherent electron transport, such as in junctions containing benzene molecules terminated by electron-withdrawing groups, e.g., benzene-1,4-dicarbonitrile. In those cases, the transport level is the unoccupied energy level formed from overlap of the molecular LUMO with the electrode levels, and the effective mass is that of the electron. However, in this work we focus on junctions with electron-donating terminal groups.