From Intermolecular Interaction Energies and Observable Shifts to Component Contributions and Back Again: A Tale of Variational Energy Decomposition Analysis

Quantum chemistry in the form of density functional theory (DFT) calculations is a powerful numerical experiment for predicting intermolecular interaction energies. However, no chemical insight gained this way beyond predictions observables. Energy decomposition analysis (EDA) can quantitatively bridge gap by providing values drivers interactions, such as permanent electrostatics, Pauli repulsion, dispersion, and charge transfer. These energetic contributions are identified performing DFT with constraints that disable components interaction. This review describes second-generation version absolutely localized molecular orbital EDA (ALMO-EDA-II). The effects different physical on changes observables structure vibrational frequencies upon complex formation characterized via adiabatic EDA. Example applications include red- versus blue-shifting hydrogen bonds; bonding frequency shifts CO, N 2 , BF bound to [Ru(II)(NH 3 ) 5 ] + moiety; nature strongly complexes between pyridine benzene naphthalene radical cations. Additionally, use ALMO-EDA-II benchmark guide development advanced force fields simulation illustrated recent, very promising, MB-UCB potential.