Semi-empirical quantum chemistry methods are based on the Hartree–Fock formalism, but make many approximations and obtain some parameters from empirical data.
They are very important in computational chemistry for treating large molecules where the full Hartree–Fock method without the approximations is too expensive.
Within the framework of Hartree–Fock calculations, some pieces of information (such as two-electron integrals) are sometimes approximated or completely omitted.
[1][2][3][4][5][6] For all valence electron systems, the extended Hückel method was proposed by Roald Hoffmann.
[7] Semi-empirical calculations are much faster than their ab initio counterparts, mostly due to the use of the zero differential overlap approximation.