Several analysis tools in ADF offer detailed insight in chemical bonding and other properties such as charges, densities and potentials. With the integrated GUI various standard and analysis options are readily accessible and easily visualized.
The energy decomposition analysis (EDA) or extended transition state (ETS) analysis1 in ADF is a powerful method to dissect the interactions that constitute a chemical bond between fragments in a molecule:
∆Ebond = ∆Estrain + ∆Eint
∆Eint = ∆Velstat + ∆EPauli + ∆Eoi + ∆Edisp
The total bonding consists of the interaction energy ∆Eint between the fragments and the strain, or preparation energy, (∆Estrain) involved in deforming the fragments to the geometries in the pro-molecule.
The interaction energy is further decomposed in terms which are meaningful in chemistry. The electrostatic attraction ∆Velstat and Pauli repulsion ∆EPauli are sometimes conveniently summed together to a steric term.2
The stabilizing orbital interactions ∆Eoi describe the orbital mixing and charge transfer between the fragments when they form the molecule. In a symmetric molecule, these can be further decomposed in the individual irreducible representations. Alternatively, an ETS-NOCV analysis3 decomposes the bonding interactions in the context of natural orbitals for chemical valence.
1 T. Ziegler & A. Rauk, Theoret. Chim. Acta 45, 1-10 (1977).
2 F. M. Bickelhaupt & E. J. Baerends, In: Reviews in Computational Chemistry Vol. 15; K. B. Lipkowitz, D. B. Boyd, Eds. (2000)
3 M. Mitoraj & A. Michalak, J Mol Model. 13, 2 (2007)