In the explicitly-unsolvable Hamiltonian for a chemical system, approximations are made to solve the energy of the system. In particular we see CNDO (ZDO), INDO and MNDO theories. CNDO - complete neglect of differential overlap; two-center electron integrals are zero. INDO - intermediate neglect of differential overlap MNDO - modified neglect of differential overlap So CNDO is easy, if orbitals arent on the same atom their integral is zero. What about INDO and MNDO? What integrals are included in INDO that arent included in CNDO? What integrals are included in MNDO that arent included in INDO? How are these integrals evaluated (parametrized)?