How to translate Curtice-Cubic Model to a Quadratic Curtice MESGET Model?

Hi,

I have a Curtice-Cubic Model (= Curtice3_Model in ADS) of a device. Is there a "simple"way, without going into the deeply maths, to translate this to a Quadratic Curtice MESFET Model (I use the Qucs MESFET model) .
The Quadratic Curtice is the Curtice2_Model in ADS I think.

Thanks.

Best regards,
JrV