The delocalization energy of molecules can be calculated approximately using the Huckel approximation, as was done originally by Huckel.

It is the spreading of valence electrons over two or more bonds in a chemical compound. In certain compounds, the valence electrons cannot be regarded as restricted to definite bonds between the atoms but move over several atoms in the molecule.

Delocalization occurs particularly when the compound contains alternating (conjugated) double or triple bonds, the delocalized electrons being those in the pi orbitals. The molecule is then more stable than it would be if the electrons were localized, an effect accounting for the properties of benzene and other aromatic compounds.

The energy difference between the actual delocalized state and a localized state is called the delocalization energy. Delocalization of electrons is a feature of metallic bonding.