Energy decomposition analysis

The energy decomposition analysis (EDA) is a powerful method for a quantitative interpretation of chemical bonds in terms of three major expressions. The instantaneous interaction energy ΔE _int between two fragments A and B in a molecule A-B is partitioned in three terms, namely, (1) the quasiclassical electrostatic interaction ΔE _elstat between the fragments, (2) the repulsive exchange (Pauli) interaction ΔE _Pauli between electrons of the two fragments having the same spin, and (3) the orbital (covalent) interaction ΔE _orb, which comes from the orbital relaxation and the orbital mixing between the fragments. The latter term can be decomposed into contributions of orbitals with different symmetry, which makes it possible to distinguish between σ, π, and δ bonding. After a short introduction into the theoretical background of the EDA, we present illustrative examples of main group and transition metal chemistry. The results show that the EDA terms can be interpreted in a chemically meaningful way, thus providing a bridge between quantum chemical calculations and heuristic bonding models of traditional chemistry.