OK, place a Schmitt trigger on the schematic and right-click on it. Below is a screen capture of this. I parameterized the logic high voltage as an example. You could just make it 4, or 5, or whatever you think is right. I also picked typical values for delay, rise time, threshold voltage, and hysteresis. You can get them from the datasheet. If you want to add input and output resistance and capacitance, you will have to add them externally.
This model is only behavioral, but is still very useful, and runs very fast.
You can, of course, do similar setups with any of the digital parts. The D FF is very useful. I made a model of a 4-bit counter using these models,and it matched the CMOS part (can't remember which one, and I think it's on my computer at work) pretty well.