A diode model looks like
.model 1N4148 D(Is=2.52n Rs=.568 N=1.752 Cjo=4p M=.4 tt=20n Iave=200m Vpk=75 mfg=OnSemi type=silicon)
If I want to model some other diode c-v curve, I can edit Cjo as needed. But what parameter would change the shape of the curve, how c declines with voltage?
I'm modeling a weird photodiode and I can get close to the actual datasheet values, but the shape is a little off.