In Equations 3-5, k 1 , k 2 , and k 3 are, respectively, the wavevectors of the hole in the left electrode, bridging molecule, and right electrode. E is the energy of the hole, x is the tunneling coordinate along the electrode-molecule-electrode axis, φ b is the height of the tunneling barrier, a is the width of the tunneling barrier, m eff is the effective mass of the hole, and h is the reduced Planck constant. φ b is defined as