Let's say you want to simulate three carbon atoms with near perfect accuracy (not considering constituent quarks, radiative effects, or relativistic effects).

Let's say you want to simulate three carbon atoms with near perfect accuracy (not considering constituent quarks, radiative effects, or relativistic effects). We'll remove the BO approximation though. So that's 2^(3 atoms * 3 coordinates * 3*12 particles) = 2^324. That's more than the number of particles in the universe. A classical computer that can handle that is simply not gonna happen. And that's just three atoms.