Development and Applications of the Density-Based Theory of Chemical Reactivity.

Density functional theory, which is well-recognized for its accuracy and efficiency, has become the workhorse for modeling the electronic structure of molecules and extended materials in recent decades. Nevertheless, establishing a density-based conceptual framework to appreciate bonding, stability, function, reactivity, and other physicochemical properties is still an unaccomplished task. In this Perspective, we at first provide an overview of the four pathways currently available in the literature to tackle the matter, including orbital-free density functional theory, conceptual density functional theory, direct use of density-associated quantities, and the information-theoretic approach. Then, we highlight several recent advances of employing these approaches to realize new understandings for chemical concepts such as covalent bonding, noncovalent interactions, cooperation, frustration, homochirality, chirality hierarchy, electrophilicity, nucleophilicity, regioselectivity, and stereoselectivity. Finally, we provide a few possibilities for the future development of this relatively uncharted territory. Opportunities are abundant, and they are all ours for the taking.