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 Δ E int between two fragments A and B in a molecule A–B is partitioned in three terms, namely, (1) the quasiclassical electrostatic interaction Δ E elstat between the fragments, (2) the repulsive exchange (Pauli) interaction Δ E Pauli between electrons of the two fragments having the same spin, and (3) the orbital (covalent) interaction Δ E 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.