The aim of this review is threefold. On the one hand, we intend it to serve as a gentle introduction to the Interacting Quantum Atoms (IQA) methodology for those unfamiliar with it. Second, we expect it to act as an up-to-date reference of recent developments related to IQA. Finally, we want it to highlight a non-exhaustive, yet representative set of showcase examples about how to use IQA to shed light in different chemical problems. To accomplish this, we start by providing a brief context to justify the development of IQA as a real space alternative to other existent energy partition schemes of the non-relativistic energy of molecules. We then introduce a self-contained algebraic derivation of the methodological IQA ecosystem as well as an overview of how these formulations vary with the level of theory employed to obtain the molecular wavefunction upon which the IQA procedure relies. Finally, we review the several applications of IQA as examined by different research groups worldwide to investigate a wide variety of chemical problems.

We propose a hierarchy of H-bond strength in terms of the single and double character of the involved donor and acceptors within different structures of (H ₂ O) ₆ .

We give a new interpretation of Resonance Assisted Hydrogen Bonds (RAHBs) in which RAHB formation leads to an overall electron localization excluding covalency as the main source of stabilization. The most relevant contributions to the RAHB energetics are electrostatics, polarization and charge transfer.

In this Perspective we review some recent advances in the concept of atoms-in-molecules from a real space perspective.