Is there a schottky diode model for the simulation?

Yes. The device model is called

sc_diode

. I do not yet have a device layout generator for it in magic, but there is a

draw_sc_diode

routine for it in the klayout pymacros.

I see files named sc_diode, but there doesn't seem to be a model in the xschem folder

Xschem is all ASCII text based, so it's easy enough to start with a symbol representing any of the diode models in the process and change the model name in the symbol to

sc_diode

. I agree it would be nice to have it in the library, but it's also nice to know that it's trivially easy to add any new component in xschem.