Abstract
Energy decomposition schemes such as SAPT, LED, and ALMO emphasize analyses of coulombic, correlative, induction, and dispersion interactions and provide useful descriptions of the attractive branch of nonbonded interactions, but these attractive interactions do not fully describe the a spherical shape of intermolecular contacts.
Kinetic energy, a separable term in the quantum mechanical energy expression complementary to potential energy, describes of exchange repulsion that is free of the challenges associated with electron density partitioning schemes. Kinetic energy-derived exchange repulsion is found to reproduce the observed angular-dependence of nonbond contacts for alkanes and halogen bonds. In addition, it can conclude that nonbond contacts/sterics is a complex interplay between kinetic energy-derived exchange repulsion and electron penetration—not simply a spherical exponential function.
Parallel spin/αα/dispersion, which survives inside the van der Waals contact distance contributes significantly to the medium-range correlation that provides stability to geminal contacts in hydrocarbons, coordination complexes, and halogen bonding.