Localization and Localizability in Quantum Organic Chemistry: Localized Orbitals and Localization Functions

The utility of the localization and localizability concepts for describing chemical situation is discussed. Two routes can be followed to get such a picture from wave functions which are in principle delocalized in nature. On the one hand are orbital localization techniques which are described in the context of their applicability to organic chemistry problems. On the other hand are methods relying on local functions which perform a partition of the molecular space into connected non overlapping regions. The Becke and Edgecombe localization function is presented in detail and its application to organic quantum chemistry reviewed.