Hi, thank you very much for your reply.

I could not understand the last statement. Did you means inter and interband model (https://optics.ansys.com/hc/en-us/articles/360042244874-Graphene-surface-conductivity-material-model)? Do we have option menu to choose from material parameter in Lumerical?

Or did you mean  fermi energy model, for Ef ≤ 0.05 eV and Ef > 0.05 eV (https://optics.ansys.com/hc/en-us/articles/360042243634-Electro-optical-modulator-based-on-a-graphene-coated-waveguide)? In this case if we bias the device with both the positive and negative voltage  then we get both positive and negative value of fermi energy. Don't we have to use both model in this case?