Guilin Sun
Ansys Employee

The built-in material mode obeys the Kramers Kronig causality. However, you could for example set the imaginary part to be zero, and refit it. There might be some difference between the original and newly set model. So you need to confirm the effectiveness.

If the new model modifies the real part too much, you may consider to sweep wavelength with the fixed real part, provided that the raw data is smooth, in order to get smooth result. You may also fix the mesh size by enforcing this:

with the minimum wavelength.