Comparison of Dispersion Models for the Silver Nanostructure in FDTD Simulations

In the time domain finite difference (FDTD) simulation of metal nanostructure, the computational accuracy strongly relies on the accuracy of the permittivity description by means of metal dispersion model over the range of wavelengths of interest. In this paper, several typical metal dispersion models for the description of silver dielectric functions are discussed, including Drude, Drude-2lorentz and Drude2cp (Critical Point) models. The deviations of the dielectric constant between the different dispersion models and the real silver are compared and analyzed. Moreover, using the FDTD method and the dispersion model, the transmission characteristics of silver nanostructure are simulated, and the effects of different dispersion models on the transmission spectra are discussed. Numerical studies show that the transmittance is affected by the dispersion model. The accuracy of the Drude model and the Drude2cp model is similar when the optical frequency is lower. The interband transition effect of the silver is enhanced when the optical frequency increases, and the precision of the Drude2cp model is significantly better than other dispersion models. The artificial red-shift of the transmission formant of silver nanostructure is discovered at higher frequency by using the Drude model and the Drude-2lorentz model. Nevertheless, the shift of transmission formant is not caused by using the Drude2cp model.