Need info on the betaeff and vdsat parameters found from simulation

That's almost certainly because you are using a vastly simplified model of MOS transistor behaviour which doesn't match current reality (even 25 years ago it was probably not valid).

There is description of how each model works in the spectre documentation which you can look at using <MMSIMinstDir>/tools/bin/cdnshelp - look under MMSim->Virtuoso SImulator Components and Device Models Reference. If you're using (say) a bsim4 model, there is a section labelled "Saturation Voltage Vdsat" (equation 21-34 onwards in MMSIM12.1, 2-37 onwards in MMSIM13.1).

In the documentation (at least in MMSIM11.1/12.1 - it's accidentally omitted in 13.1 - which is being corrected) - it tells you that betaeff is defined this way:

betaeff = ueff * coxe * weff / leff

You can find some other posts which talk about how ueff and cox are formed - but you may need to consult with the bsim4 documentation from Berkeley to see all of the equations. This is of course assuming that it's bsim4 that you're using - the equations will be different for different models...

Regards,

Andrew.