Nonlinear capacitor in XFDTD

Hi Everyone!

I have a problem with using nonlinear capacitors in Remcom XFDTD.
After calculations in response I have only one harmonic(incident frequency)
and no one on other frequencies(such as 2f? 3f etc).

Question:
How to specify nonlinear capacitor in XFDTD correctly?


Thanks!

May be any one can present examples or projects
with using nonlinear capacitors in XFDTD