# How to Model Drude Materials using FDTD

by thepolishman
Tags: computational, drude, fdtd, light interaction, materials, metals, model
 P: 5 Hello all, I have been learning to use FDTD to model light interaction with various materials. I've successfully managed to model light interaction with semiconductors/insulators. However, I've been having trouble understanding how to incorporate metals into this model. The code becomes unstable whenever I give it a negative or imaginary permittivity. One of the methods used to circumvent this problem is to model the metal as a Drude material, as outlined in this FDTD help guide: http://www.eecs.wsu.edu/~schneidj/ufdtd/chap10.pdf After incorporating the equations shown in Section 10.4 in the link above, I still can't use any negative or imaginary permittivities in my code. I'm fairly certain I did not make any coding errors. My guess is that I have to incorporate this negative or imaginary permittivity indirectly somehow. The problem is, I don't know how. Any help regarding how to correctly implement this model (or possibly an alternative one, as I'm aware that there are others) would be greatly appreciated.
 Sci Advisor P: 3,267 First, it would have been nice to write out what FDTD stands for (Finite Difference Time Domain) instead of leaving it to us to find out. Maybe the point is only how to specify the susceptibility:In the Drude model is that the complex value of the susceptibility arises once you specify a positive value for the damping g. So you don't have to enter any negative or complex values explicitly. You could also try to split the complex susceptibility into its (positive) real part and the imaginary part and treat the latter as a real conductivity term. If this doesn't solve your problem, it is rather difficult to propose a solution as I can't tell you what goes wrong without knowing your code.

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