Hi Joe,

I personally don't really have  any experience with k.p models, so I don't think I will be much help; hopefully someone else on the mailing list will be better able to. That being said, these high-k modes are surely present even in the continuum, no? They are a consequence of the k.p model you are using, *not* the discretization, so I would agree with what Rafal said: that you need to make sure your model is valid at the energies you care about first before discretizing.

I see what you’re saying. Yes, The high-k modes are present in the continuum; they’re just ignored because they’re outside the Brillouin zone.

The idea of adding "dummy" degrees of freedom and a coupling to open up a gap seems reasonable. You could also just calculate the scattering matrix *with* the high-k modes included and see whether there is any scattering to/from the low-k modes. If there's not you might be able to get away with not doing anything about them at all?

I was also wondering if there was much coupling between the high- and low-k modes. How would I extract that info from the scattering matrix?

Thanks.

-Leon