Modified Debye model parameters of metals applicable for broadband calculations

The finite-difference time-domain method can provide broadband results if the excitation source is a pulse. This demands that the parameters of modeled materials have to be applicable over broad frequency bands. We optimize the modified Debye model parameters for gold, silver, copper, platinum, and aluminum using a large-scale nonlinear optimization algorithm. The complex relative permittivities calculated using the optimized parameters agree well with experimental values over broad frequency bands. The associated root-mean-square deviations are 0.49%, 3.52%, 4.13%, 1.64%, and 0.66%, respectively. We also provide an example of broadband calculations. The obtained broadband results are verified by a series of steady-state calculations.