How to simulate finfet in ltspice?
First find a model: an example of a Finfet model can be found here.

Then you need to import the model in to LT spice. 

Remember spice is only for modeling circuits, it doesn't always reflect what happens int the real world. Spice is really only a text file, graphical packages only generate the spice netlist, it is important to understand the spice code. In Lt spice this can be located under view->spice netlist