However, ligand field theory is less artificial, allows for electron delocalization, and is more readily extended to more complex patterns of bonding between the central metal ion and the ligands (such as the incorporation of bonds with π symmetry).
A superior theory is a modification of crystal field theory known as ligand field theory, which is more securely based in MO theory and allows for a more appropriate degree of delocalization of electrons over the metal ion and the ligands.
The chemical bond between the metal and the ligands and the origins of orbital splitting are ascribed not only to electrostatic forces but also to a small degree of overlap of metal and ligand orbitals and a delocalization of metal and ligand electrons.
In another theory, called the molecular orbital theory also applied to coordination compounds complete mixing of metal and ligand orbitals (to form molecular orbitals) and complete delocalization of electrons are assumed.
This formalism does not acknowledge the delocalization of electron density from the metal to the ligand, but the chemical properties of the carbonyl anions do suggest that some of the negative charge resides on the metal.
The British scientist J.D. Bernal predicted in 1928 that all matter should ultimately become metallic at sufficient pressure, as the forced overlap of electron orbitals induces electron delocalization.
The Socialist Party talks fairly vaguely about its interest in a Danish model called "flexicurity," which exchanges job security for a supple approach to hours, pay and delocalization.
Other theories suggest a process called carrier leakage, in which at high currents the carriers start to spill away from areas of high performance, or another process, called carrier delocalization, where electrons simply fail to find a paired hole at high electric currents because they are pulled away from the active region where electrons and holes are supposed to recombine and emit light.
To the objection from delocalization, they argue that all the structural account requires is that some part of the total electron density of the molecule is responsible for the features associated with the bond and there need be no assumption that it is localized directly between the atoms as in Lewis' model (Hendry, 2008,2008b).
