A Chemically Meaningful Measure of Electron Localization.
Journal article, 2015
Electron localization and delocalization are commonly invoked in the day-to-day rationalization of chem. This work addresses the challenges of quantifying this elusive concept in a chem. useful manner. A general principle, requiring the simultaneous quantification of (1) a limited phys. vol. (classical criterion) and (2) same-spin loneliness (quantum criterion), is introduced. It is demonstrated how, by beginning with the Electron Localization Function (ELF) scalar field, one can choose to discard all points in space where the same-spin loneliness is lower than a certain value. Such a partitioning approach ensures that both criteria for quantifying localization (1 and 2) are simultaneously met. The most chem. instructive results arise when the dividing boundary condition is set by the local behavior of a homogeneous electron gas. The High Electron Localization domain Population (HELP) is introduced and applied for quantifying the localization of individual domains within mols., as well as a measure of total electron localization in atoms and mols. Several striking agreements with chem. intuition, exptl. measurable quantities, and quantum chem. constructs are demonstrated along with understandable differences. Studies of diat. mols. agree with current ideas on chem. bonding. The size-dependence and magnitude of localization in linear hydrocarbons is studied and compared to cyclic systems, such as benzene. The proposed methodol. offers a straightforward measure for direct and quant. comparisons between atoms, mols., and extended condensed matter. [on SciFinder(R)]
quantum chemical topology