SEARCH Articles Figures Tables Approximate Molecular Orbital Theory for 4-Electron 3-Centre Bonding Units Centre Molecular Orbitals and Pauling 3-Electron Bonds Centring of the atomic orbital Delocalized Molecular Orbital Theory for 4-Electron 3-Centre Bonding Units Increased-Valence Structures with three 2-Centre Bond Orbitals Muffin-Tin Orbitals and One-Centre Expansion Three-centred orbitals