@User for montecarlo you need to use the 'mc' process corner in the .lib, for device mismatch use tt_mm corner. You don't need to set the mc_mm_switch variable, this is done in the .lib file once you select a mismatch or MC corner.

Strange... the inverter circuit, if made with 1.8 V devices, works. WIth 5V devices, the mc corner doesn't work at all and the simulation crashes.

@User this may be because montecarlo is not (yet) available for these devices? I don't know the answer, may be @User knows.

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@User just a quick test, try to assign L=0.5 and W=1, see if it does better...

Ah... it was the problem

High voltage transistors have some limits on W and L, the higher the voltage the less the freedom for the designer :-)

Another point for continuous W and L models. I hope we will have it soon.