Toward a Consistent Interpretation of the QTAIM: Tortuous Link between Chemical Bonds, Interactions, and Bond/Line Paths

Abstract

Currently, bonding analysis of molecules based on the Quantum Theory of Atoms in Molecules (QTAIM) is popular; however, "misinterpretations" of the QTAIM analysis are also very frequent. In this contribution the chemical relevance of the bond path as one of the key topological entities emerging from the QTAIM's topological analysis of the one-electron density is reconsidered. The role of nuclear vibrations on the topological analysis is investigated demonstrating that the bond paths are not indicators of chemical bonds. Also, it is argued that the detection of the bond paths is not necessary for the "interaction" to be present between two atoms in a molecule. The conceptual disentanglement of chemical bonds/interactions from the bonds paths, which are alternatively termed "line paths" in this contribution, dismisses many superficial inconsistencies. Such inconsistencies emerge from the presence/absence of the line paths in places of a molecule in which chemical intuition or alternative bonding analysis does not support the presence/absence of a chemical bond. Moreover, computational QTAIM studies have been performed on some "problematic" molecules, which were considered previously by other authors, and the role of nuclear vibrations on presence/absence of the line paths is studied demonstrating that a bonding pattern consistent with other theoretical schemes appears after a careful QTAIM analysis and a new "interpretation" of data is performed.

Evaluating common QTAIM and NCI interpretations of the electron density concentration through IQA interaction energies and 1D cross-sections of the electron and deformation density distributions

“…[28]. Although many regard the debate to be stale [37,38], new papers are still being published regarding the interpretation and physical nature of AILs [39][40][41][42][43][44][45][46]. NCI managed to solve one branch of QTAIM-associated problems, by showing that the absence of an AIL does not imply that electron density cannot be concentrated in the bonding region of an interaction.…”

To What Extent are “Atoms in Molecules” Structures of Hydrocarbons Reproducible from the Promolecule Electron Densities?

“…On the other hand, what triggers an additional ambiguity is the presence of (3, À1) CPs between atoms in molecules (AIM), both in intra-and intermolecular cases, that few chemists are willing to conceive ac hemical bond in between. [4,5] It is also tempting to assume that two AIM with a( 3, À1) CP in between are more strongly interacting than those without; however,t his interpretationi s not in line with what is known from the general theory of intermolecular forces. [5,7] One may sum up and claim that there is no universal one-to-onee quivalence betweent he presence of the (3, À1) CPs and the presence of chemical bonds or strongi nteractions.…”

“…[4,5] It is also tempting to assume that two AIM with a( 3, À1) CP in between are more strongly interacting than those without; however,t his interpretationi s not in line with what is known from the general theory of intermolecular forces. [5,7] One may sum up and claim that there is no universal one-to-onee quivalence betweent he presence of the (3, À1) CPs and the presence of chemical bonds or strongi nteractions. By dismissing this unacceptable equivalence,m ost, if not all, controversies surrounding the QTAIM applications are resolved.…”

“…[1][2][3] Unfortunately,concomitantly,misinterpretations of the QTAIM analysis have also grown rapidly, triggering controversies aroundt he theory (for ac omprehensive bibliography of the past controversies see the literature in refs. [4] and [5]). In the heart of these controversies is the question of whether the presence/absence of a( 3, À1) critical point (CP) between two atomsi namolecule, emerging from the topological analysiso ft he molecular electron densities, is indicative of the presence/absence of ac hemical bond.…”

Six questions on topology in theoretical chemistry

“…Since subjective elements are always involved in constructing correspondence rules, the emerging classifications always have vague "borderlines". Thus, the initial floppiness remains even after "quantification" [48].…”