SEARCH Articles Figures Tables Approximate Molecular Orbital Theory for 4-Electron 3-Centre Bonding Units Approximate theory Computational quantum mechanics approximate orbital theories Integral approximation, semiempirical molecular orbital theory MNDO approximation, semiempirical molecular orbital theory Molecular orbital theory Hartree-Fock self-consistent field approximation Molecular orbital theory approximate Molecular orbital theory approximate methods Molecular orbital theory approximation Molecular orbital theory tight-binding approximation Orbital approximation Orbitals approximation Simple Hiickel molecular orbital theory approximations