Drude Model

I have a question regarding this tool. Here if we simulate the theoretical models the equation for example drude model defined as drude free electron theory model defined in Johnson & Christy’s Physical review paper . epsilon(w)=1-(plasma freq)^2/omega(omega+i*collision frequency) but the drude model permittivity of present FDTD model defined as epsilon(w)=epsilon infinity-(plasma freq)^2/omega(omega+i*collision frequency). so to make the use of FDTD simulation tools as well as EM Solvers what should we put as epsilon infinity. If we place this value is 1 then the values going to be changed.

Please suggest a convincing way.

Best Regards