What does shape a topological atom?
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In this pedagogical communication after demonstrating the legitimacy for using the quantum theory of atoms in molecules (QTAIM) to non-Coulombic systems, Hookean H2 +/H3 2+ species are used for AIM analysis. In these systems, in contrast to their Coulombic counterparts, electron density is atom-like and instead of expected two/three topological atoms, just a single topological atom emerges. This observation is used to demonstrate that what is really “seen” by the topological analysis of electron densities is the clustering of electrons. The very trait of monotonic decay of electron density around the “centers” of clustering guarantees the appearance of topological atoms as basin of attraction of the gradient vector field of the electron density. Although observations with Hookean molecules may seem disappointing at first glance, a careful reasoning points to the fact that the QTAIM methodology is extendable to novel domains, by a knowledge of the morphology of underlying densities, beyond the typical Coulombic systems.
KeywordsQuantum theory of atoms in molecules Topological atoms Monotonic electron density Hookean model of molecules Non-Coulombic potential energies
Shant Shahbazian is grateful to Mr. Shahin Sowlati, Dr. Rohoullah Firouzi, Miss. Masume Gharabaghi and Dr. Cina Foroutan-Nejad for a detailed reading of a previous draft of this paper and their fruitful comments and suggestions.
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