The integration in Eq 1 is apparently not easy to perform due to the complex mathematical form of Fermi function and density of state. There is no simple analytical relation for current and voltage to be used for experimental data analysis. Various approximated modeling methods have been invented and applied to fit the experimental I-V results to extract transport parameters like coupling strength (Γ) and energy offset (ε0) . The first one is to perform numerical integration of Eq 1. By decreasing the step size in the numerical integration, a high accuracy can be achieved. On other hand, when the Fermi broadening is small relative to the density of states, or if at low temperature, the Fermi function in Eq 1 can be approximated by a step function, and an analytical expression of I-V can be obtained as