Local Exchange Integrand: Looking into Quantum Contributions to Chemical Bonds

In this work, we present maps of the integrand of the exchange energy <i>K</i>(<i>r</i>₁,<i>r</i>₂) in terms of atomic contributions. This quantity helps to improve the understanding of this quantum correction in chemical bonding. With a set of covalent and noncovalent diatomic molecules, we show that it is possible to develop useful vocabularies for identifying regions where the exchange correction removes or adds electrons predicted by the classical Coulomb term. Applying the results to four halogen-bonded complexes, we prove that it is possible to gain a further understanding of the characteristics of the interaction between them and to offer a complete description of the anisotropy of the σ hole. The results are confirmed by molecular orbital, NBO, and SAPT(DFT) analyses and bode well for the use of <i>K</i>(<i>r</i>₁,<i>r</i>₂) in chemical bond analysis.