Electronic Stress as a Guiding Force for Chemical Bonding

In the electron-preceding picture of chemical change, the paramount problem is identifying favorable changes in electronic structure. The electronic stress tensor provides this information; its eigenvectors represent electronic normal modes, pointing the way towards energetically favorable (or unfavorable) chemical rearrangements. The resulting method is well founded in both density functional theory and the quantum theory of atoms in molecules (QTAIM). Stress tensor analysis is a natural way to extend the QTAIM to address chemical reactivity. The definition and basic properties of the electronic stress tensor are reviewed and the inherent ambiguity of the stress tensor is discussed. Extending previous work in which the stress tensor was used to analyze hydrogen-bonding patterns, this work focuses on chemical bonding patterns in organic reactions. Other related material (charge-shift bonding, links to the second-density-derivative tensor) is summarized and reviewed. The stress tensor provides a multifaceted characterization of bonding and can be used to predict and describe bond formation and migration.