Quantum chemical topology: On bonds and potentials

In this essay-like review two different aspects of the "Quantum Chemical Topology" (QCT) approach are critically discussed at great length. One is the ability to compute bonding patterns in single molecules, complexes or crystals based on the topology of the electron density, via the concept of the bond path. The other aspect is the development of an intermolecular potential based on multipole moments of topological atoms. Although bond paths have been embraced by a wide community and successfully applied to reveal interesting insights, there is an ongoing debate about their interpretation. The ongoing work on QCT potentials leads to a consistent force field for proteins and liquid water. Radical ideas on the modelling of polarisation, the short-range regime, overlap, and the nature of quantum delocalisation are presented.