Well,
AS/AD/PS/PD is needed if option CALCACM is used...
Please also refer to tsxx spice model file.
New parameter "CALCACM" is added in the H97.4.1
* In H97.2 & H97.4, the default values of AS/AD and PS/PD are zero when BSIM3v3.1
* model with ACM=12 is used. This results in zero junction capacitance and incorrect
* junction leakage current, if AS/AD and PS/PD are not specified in the netlist. In
* H97.4.1, with CALCACM > 0, the default calculation of AS/AD and PS/PD will be
* calculated using HDIF, if AS/AD and PS/PD are not specified in the netlist.However
* with CALCACM=0, the default is zero for AS/AD and PS/PD.
How to well define those?? I have no idea....
It can be accomplished by doing try and error plus a certain experience, or ask layout to have Layout Parasitic Extraction (LPE) for you.
Of course, you have to put efforts to back annotate it...
The easiest way to do is assume larger ones instead...