Selected face treated as rigid in solidworks simulation

I would like to set a particular face in my part to be rigid in the simulation. I am basically doing a tensile stiffness test; I have fixed one end of a part and applied a load to the other end. I want to know the displacement of the loaded end, but the face is not rigid so the result is a kind of dome-ed geometry. Is there a way to set a particular face to be rigid (i.e. all nodes on the face maintain their position relative to one another) while allowing the rest of the part to deform?

Thanks!

SolidworksSimulation