The Lewis electron-pair bonding model: modern energy decomposition analysis

Breaking down the calculated interaction energy between two or more fragments into well-defined terms enables a physically meaningful understanding of chemical bonding. Energy decomposition analysis (EDA) is a powerful method that connects the results of accurate quantum chemical calculations with the Lewis electron-pair bonding model. The combination of EDA with natural orbitals for chemical valence (NOCV) links the heuristic Lewis picture with quantitative molecular orbital theory complemented by Pauli repulsion and Coulombic interactions. The EDA-NOCV method affords results that provide a physically sound picture of chemical bonding between any atoms. We present and discuss results for the prototypical main-group diatomics H2, N2, CO and BF, before comparing bonding in N2 and C2H2 with that in heavier homologues. The discussion on multiply bonded species is continued with a description of B2 and its N-heterocyclic carbene adducts. This Perspective introduces energy decomposition analysis as a means of providing a quantum chemically derived bonding model that we can use to rationalize molecular geometries and bonding. The model serves as a bridge between the simple Lewis electron-pair bond and the complicated quantum theoretical nature of the chemical bond.