Quantum physics is referred to as an ab initio model because it uses fundamental principles and basic equations to calculate properties of systems from scratch without resorting to empirical or semi-empirical data.

Classical mechanics is not commonly referred to as an ab initio model. Instead, it is based on fundamental laws and principles that describe the motion of macroscopic objects, but it is not typically categorized as ab initio like quantum physics.

Classical electromagnetism can be considered an ab initio model as it is grounded on basic principles, such as Maxwell’s equations, which describe electromagnetic phenomena without using empirical data. The first principles in classical electromagnetism include Coulomb’s law, Biot-Savart’s law, Ampère’s law, and Maxwell’s equations.