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.