where ε(∞) is the real part permittivity at high frequency, which is the sum of ε(∞) from both Drude and Lorenz models, ω P,D is the plasma frequency of the Drude model, Γ D is the dumping constant of the Drude model, ω P,L, j is the plasma frequency of the Lorenz model, ω 0, j is the central angular frequency in the Lorenz model, Γ L, j is the dumping constant of the Lorenz model, j is the indicator number, which is connected to the number of oscillation, 1 or 2 is used in this study.