In method 1, the energy step for numerical integration was set to be 0.2 meV and lower and upper limit of the integration is -5 eV and 5 eV. It should be emphasized that the integration step size should be significantly smaller than the width of the transmission peak, which is defined by the coupling parameter in Eq 1.3. We found this step size and integration limit are generally enough even down to the 1 meV coupling situation, and further smaller step size and wider integration range produce none noticeable difference in I-V plot. At last, the thermal energy (KBT) in the Fermi function in Eq 1 was set to be 0.025 eV for room temperature (298K).