Forced Bonding and QTAIM Deficiencies: A Case Study of the Nature of Interactions in He@Adamantane and the Origin of the High Metastability

Abstract

Calculations within the framework of the interacting quantum atoms (IQA) approach have shown that the interactions of the helium atom with both tertiary, tC, and secondary, sC, carbon atoms in the metastable He@adamantane (He@adam) endohedral complex are bonding in nature, whereas the earlier study performed within the framework of Bader's quantum theory of atoms in molecules (QTAIM) revealed that only He---tC interactions are bonding. The He---tC and He---sC bonding interactions are shown to be forced by the high pressure that the helium and carbon atoms exert upon each other in He@adam. The occurrence of a bonding interaction between the helium and sC atoms, which are not linked by a bond path, clearly shows that the lack of a bond path between two atoms does not necessarily indicate the lack of a bonding interaction, as is asserted by QTAIM. IQA calculations showed that not only the destabilization of the adamantane cage, but also a huge internal destabilization of the helium atom, contribute to the metastability of He@adam, these contributions being roughly equal. This result disproves previous opinions based on QTAIM analysis that only the destabilization of the adamantane cage accounts for the endothermicity of He@adam. Also, it was found that there is no homeomorphism of the ρ(r) and -v(r) fields of He@adam. Comparison of the IQA and QTAIM results on the interactions in He@adam exposes other deficiencies of the QTAIM approach. The reasons for the deficiencies in the QTAIM approach are analyzed.

On the Uselessness of Bond Paths Linking Distant Atoms and on the Violation of the Concept of Privileged Exchange Channels

“…Despite the attractiveness of the concept of privileged exchange channels and its certain acceptance, we will show, however, that this concept is incomplete or even incorrect. The possible cause of the lack of confirmation and possible erroneousness of this concept will also be given.…”

Bond paths between distant atoms do not necessarily indicate dominant interactions

“…Recently, Pendás and his collaborators and then Tognetti and Joubert, and Dem'yanov and Polestshuk have made considerable progress in clarifying the reason for the presence of bond paths between pairs of bonded atoms. Namely, by decomposing the IQA‐based interatomic interaction energy on the electrostatic energy and the exchange‐correlation energy (see the Methodology section) the first authors have showed that the presence of a bond path is closely related to the latter of these two components, i.e., to the exchange‐correlation energy (or, more precisely, to the exchange energy).…”

Hydrogen–hydrogen bonding: The current density perspective

“…The empirical observation of a homeomorphism between the density and the virial field actually served as a justification of the physical meaning of BCPs . Despite the report of exceptions, this homeomorphism does hold for all the molecules investigated in Ref. .…”