Journal Article atoms in molecules conceptual density functional theory AIM Fukui function Heisenberg Equation of motion Kullback-Leibler QTAIM Quantum Theory of Atoms in Molecules Research Support, U.S. Gov't, Non-P.H.S. atomic properties chemical reactivity density functional theory ehrenfest force electron density general‐purpose reactivity indicator hirshfeld partitioning information-theoretic fitting least squares linear response function probabilty density fitting quantum theory of atoms in molecules radical addition reactions relativity scalar relativistic zeroth-order regular approximation softness kernel stockholder population analysis two-component zero-flux condition zero-flux surface