the ab initio way explanation

ab initio model is a model that makes use of fundamental physics law to approach a problem

quantum physics will be an ab initio model if the problem we’re trying to solve makes use of a fundamental physics law; and for quantum mechanics its funamental physics will be the use of Schrodinger’s equation, wave-particle duality, quantisation of energy and also wave function, so if a model consider this funamental physics law then we can say it is a quantum physics ab initio model

same as classical model, the fundamental physics will be the use of Newtons three law

Similarly, classical electromagnetism can be used as an ab initio framework. Its first principles are Maxwell’s four equations, together with the Lorentz force law, which describe the behaviour of electric and magnetic fields and their interactions with charged particles.