You're a Chemist, why are you doing quantum Physics?
Because I had a choice of going in the QM direction or the MM (Molecular Mechanics) direction, MM isn't even taught in my degree and I will not be able to write my thesis on it... and everything else in chemistry is physics anyway, so short of doing thermodynamics I don't really have any other options if I want the computational degree.
Also because I love quantum physics. Am I supposed to call it quantum chemistry? It's all kind of the same from a slightly different angle, anyway.