Information theoretic approach to molecular and reactive systems

The information-theoretic basis of the “stockholder” partitioning of the molecular electron density into fragment densities is reexamined in terms of the variational principles for alternative measures of the minimum information distance between the subsystem densities and promolecule electron distribution, for which the Hirshfeld scheme represents the optimum division. The local equalization of the subsystem information distance densities is discussed and illustrated for selected diatomics and triatomics. Approximate relations between the information content diagrams and familiar density difference plots of quantum chemistry are explored and the surprisal analysis of the molecular electron density is advocated as the entropic complement of to the familiar density difference diagrams. The generalized forces (affinities) and the Fukui function quantities of the Hirshfeld reactants in the donor-acceptor reactive system are examined. These affinities, combining both the information entropy and the Fukui function information, drive the charge transfer processes between the subsystems. Various Fukui function descriptors of acidic and basic reactants are defined and the associated minimum entropy deficiency rule for the Fukui function “distributions” is established.