configuration interaction method, this approximation allows one to treat the Schrödinger equation as a "simple" eigenvalue equation of the electronic molecular Hamiltonian , with a discrete set of solutions. Contents 1 Accuracy and scaling 1.1 Linear scaling approaches 2 Classes of methods 2.1 Hartree–Fock methods 2.2 Post-Hartree–Fock methods 2.3 Multi-reference methods