1. Quantum physics is the ab initio model because it is underlying on the Schrödinger equation.
2. Classical physics is the ab initio model because it is underlying on the Newton equations.
3. The classical electromagnetism is the ab initio model because it is underlying on the Maxwell equations.
There are the 3 tasks in quantum chemistry that have the precise solutions of the Schrodinger equation: the hydrogen atom, the molecular ion of hydrogen, the molecule of hydrogen. The precise solution of the Schrodinger equation for the hydrogen atom we receive in spherical coordinates, the solutions for other two task we receive in elliptical coordinates. These are an ab initio solutions.
The main problem of ab initio solution for other molecules is the calculation of quantum chemistry integrals (matrix elements of Hamiltonian) on several centers. This problem can be solved by a replace of the real quantum chemistry integral on ionization potentials. This method is called Huckel method. This is no ab initio method, this is a semiempirical method.