Personally, I work in the field of Optics and use computer simulations all the time.
In two different internships I've used large scale computations:
In the simulation of laser pulse propagation, where I modeled quantum systems interacting with the laser field
In the simulation of the optical response of complex surfaces, where I solved eigenvalue problems for specific structures.
Honestly, once you have a good knowledge in computer simulation and numerical calculations, then adapting them to different physical systems is not too hard. I even have a friend who does the same type of research I do but followed a mathematics MSc. And her thesis is on signal treatment for gravitational waves, which is not a particularly easy field, but she does just fine.