Testing different methods, we arrive at a conclusion that calculating the complex permittivity directly from the polarization autocorrelation function (ϕ) proves to be more efficient and clearer compared to employing its derivative. Primarily, a continuous relaxation time distribution model is adopted to calculate the Debye relaxations of the spectra. This method represents ϕ(t) as a superposition of exponential decay functions that follow continuous relaxation time distribution g(τ ).