ETS-NOCV is a powerful tool to quantitatively analyze chemical bonds, combining the extended transition state (ETS) method for energy decomposition analysis combined with the natural orbitals for chemical valence (NOCV) theory. It is also known as EDA-NOCV (Energy Decomposition Analysis).
With the ETS-NOCV charge and energy decomposition scheme the deformation density is partitioned into the different components (σ, π, δ) of the chemical bond being analyzed (see also the manual). The energy contributions to the total bond energy is calculated for each specific orbital interaction between fragments, giving insight in the orbital interactions also for non-symmetric molecules.
The ETS-NOCV analysis offers a compact quantitative picture of the chemical bond, which is also qualitatively attractive to chemists. Since recently the analysis has been extended to periodic systems (see tutorial), so that one can also analyze adsorbate-surface bonding and the interaction of molecules with porous frameworks.