Quantum Mechanics: Schrodinger’s equation forms the basis of describing a natural system from nano-scale to meso-scale physics, determining the evolution of system through time, which is closely replicates the nature in a mathematical way. It cannot be broken down into fragments to reveal any basic structure(equation).

Classical Mechanics:It perfectly describes the macroscopic world through Newtonian Mechanics and later through Lagragian and Hamiltonian Mechanics. it perfectly fits the empirical data thus describing the observable world.

Classical electromagnetism: It is an ab initio model if we consider only the fundamental charge carrier electron. But a more refined theory that could be counted as the ab initio would be quantum electrodynamics, which explains light-matter interactions.

Thus making quantum mechanics a truly ab-initio model.