There are a couple of MOSFET Models available, the last one I came across was BSIM4 (for deep-sub-Mircon <100 nm) and BSIM3 which ought to be good enough down to 180 nm.
@David, your Simulator uses the most simplest (and fastest) Model which is know as a first generation model for default.
So, the 3rd generation model, quite more complicated has a couple of more parameters to tune. Here is the documentation from ngspice, btw. the best FOSS spice simulator we can use.
http://ngspice.sourceforge.net/external-documents/models/bsim330_manual.pdf
We need reasonable values for *all* parameters!