Atoms in Molecules

The quantum theory of atoms in molecules (QTAIM) was developed by Professor Richard Bader since the early 1960s, during the past decades QTAIM has gradually become a theory for addressing possible questions regarding chemical systems, in a variety of situations hardly handled before by any other model or theory in Chemistry. QTAIM recovers the central operational concepts of the molecular structure hypothesis, that of a functional grouping of atoms with an additive and characteristic set of properties, together with a definition of the bonds that link the atoms and impart the structure. QTAIM approach defines chemical bonding and structure of a chemical system based on the topology of the electron density. In addition to bonding, AIM allows the calculation of certain physical properties on a per-atom basis, by dividing space up into atomic volumes containing exactly one nucleus, which acts as a local attractor of the electron density. In QTAIM an atom is defined as a proper open system, i.e. a system that can share energy and electron density, which is localized in the 3D space. The mathematical study of these features is usually referred in the literature as charge density topology.

The electron density describes the manner in which the electronic charge is distributed throughout real space in the attractive field exerted by the nuclei.

According to the theorems of QTAIM, the molecular structure is given by the stationary points of the electron density.