I have tried to regenerate the result from drude-lorentz model in the article "Ultra-broadband THz time-domain spectroscopy of common polymers using THz air photonics". The dielectric number of PA6(figure 2 below). my result is very similar to the results but are not equal. I have multiplied both oscillator strength and resonance frequency in 2*pi but the damping coefficient has not been multiplied.
in both COMSOL and MATLAB my results are similar but are different from the article. I think the problem must be about the coefficients in table 2 of the paper.