  The chemical bond is an important local concept to understand chemical
compounds and processes. Unfortunately, like most local concepts, the chemical
bond and the bond order do not correspond to any physical observable and thus
cannot be determined as an expectation value of a quantum chemical operator. We
recently demonstrated [Boguslawski et al., J. Chem. Theory Comput., 2013, 9,
2959--2973] that one- and two-orbital-based entanglement measures can be
applied to interpret electronic wave functions in terms of orbital correlation.
Orbital entanglement emerged to be a powerful tool to provide a qualitative
understanding of bond-forming and bond-breaking processes, and allowed for an
estimation of bond orders of simple diatomic molecules beyond the classical
bonding models. In this article we demonstrate that the orbital entanglement
analysis can be extended to polyatomic molecules to understand chemical
bonding.
