# The correlation theory of the chemical bond. (arXiv:1605.06919v3 [quant-ph] UPDATED)

The quantum mechanical description of the chemical bond is generally given in

terms of delocalized bonding orbitals, or, alternatively, in terms of

correlations of occupations of localised orbitals. However, in the latter case,

multiorbital correlations were treated only in terms of two-orbital

correlations, although the structure of multiorbital correlations is far

richer; and, in the case of bonds established by more than two electrons,

multiorbital correlations represent a more natural point of view. Here, for the

first time, we introduce the true multiorbital correlation theory, consisting

of a framework for handling the structure of multiorbital correlations, a

toolbox of true multiorbital correlation measures, and the formulation of the

multiorbital correlation clustering, together with an algorithm for obtaining

that. These make it possible to characterise quantitatively, how well a bonding

picture describes the chemical system. As proof of concept, we apply the theory

for the investigation of the bond structures of several molecules. We show that

the non-existence of well-defined multiorbital correlation clustering provides

a reason for debated bonding picture.