Energy Decomposition Analysis of the Chemical Bond: Scope and Limitation

We introduce and discuss the basics of the energy decomposition analysis (EDA), which is a powerful method that connects the results of accurate quantum chemical calculations with the Lewis electron-pair bonding model. The breakdown of the calculated interaction energy between two or more fragments into well-defined terms makes it possible to model the nature of the chemical bond in a physically meaningful way. The EDA focuses on the formation of the chemical bond rather than on the mere description of the finally formed electronic structure of a molecule. This distinguishes the EDA from the most of the other approaches of analysing a chemical bond. The consideration of various electronic states, charges and electron configurations of the fragments in EDA makes it possible to identify the best-suited fragments for the description of the bond and it provides deep insight into the interatomic interactions during bond formation. The combination of the EDA with natural orbitals for chemical valence (NOCV) connects the heuristic Lewis picture with quantitative MO theory complemented by Pauli repulsion and Coulombic interactions. The results of the EDA-NOCV method provide a physically sound picture of the chemical bonds of atoms across the periodic table. This review discusses the scope but also the limitation of the EDA-NOCV method. Results are presented for first-row diatomic molecules and for compounds of main-group atoms, transition metals, lanthanides and actinides.