Quantum-based material’s calculations are simulation, the theoretical aspect is the Schrodinger equation itself. You are not actively trying to justify or create the Schrodinger equation, we know it works and we are now using it to simulate and calculate.
I think quantum mechanics is viewed by many as a completely theoretical field, as for example the first scientists that come to mind are the founders of this field, who did in fact do theoretical work. However, the field is now much further, and both the experimental (ex. quantum computing) and simulation activity (ex. ab initio calculations) is present.