Meep's ability to work with negative epsilon

[leSemaleon]

I work in the THz range. For copper, for example, in this range dielectric constant is approximately $\hat{\varepsilon}=-75e3+i1.5e6$. How can this be indicated in the material?

[stevengj]

This is a FAQ: https://meep.readthedocs.io/en/latest/FAQ/#why-does-my-simulation-diverge-if-the-permittivity-is-less-than-0

You can have a negative ε in Meep, but it must be done by introducing a dispersive material. This is fundamental to Maxwell's equations in the time domain.

[stevengj]

That being said, in the THz range where the conductivity is that high, the skin depth will be extremely small, so you will have difficulty resolving the penetration of the field into the metal with your grid.

You might be better off putting in the metal as a PEC, and then putting in the effect of absorption perturbatively. (People in the FEM world do something similar with impedance boundary conditions, which give a first-order approximation to Ohmic losses.)