A Drude-Lorentz mode for better fitting the gold permittivity from experimental data (Johnson and Christy) is base on this paper:
"Improved analytical fit of gold dispersion: Application to the modeling of extinction spectra with a finite-difference time-domain method", Phys. Rev. B 71, 085416 (2005) PDF
"Improved analytical fit of gold dispersion: Application to the modeling of extinction spectra with a finite-difference time-domain method", Phys. Rev. B 71, 085416 (2005) PDF
The real and imag part is plotted as below with a Python code: