Generalization of the LorentzPole model of the permittivity:

\TField{\varepsilon}^{(\mathrm{rel})} & = & \frac{i\sigma_{\varepsilon}}{\omega-\omega_{p}}+\frac{i\sigma_{\varepsilon}^{\ast}}{\omega+\omega_{p}^{\ast}}

In some publications this model is named critical point model. See [1] and [2] for more details.

[1]Etchegoin, P. G., Le Ru, E. C., & Meyer, M. (2006). An analytic model for the optical properties of gold. The Journal of chemical physics, 125(16), 164705.
[2]Sehmi, H.S., Langbein, W. and Muljarov, E.A., 2017. Optimizing the Drude-Lorentz model for material permittivity: method, program, and examples for gold, silver, and copper. Physical Review B, 95(11), p.115444.