Can Aromaticity be Evaluated Using Atomic Partitions based on the Hilbert-space?

Kimika Teorikoa Seminar

Aromaticity is a fundamental concept in chemistry that
explains the stability and reactivity of many compounds by
identifying atoms within a molecule that form an aromatic
ring. Reliable aromaticity indices focus on electron
delocalization and depend on atomic partitions, which give

rise to the concept of an atom-in-the-molecule (AIM). Real-
space atomic partitions present two important drawbacks: a

high computational cost and numerical errors, limiting
aromaticity measures to medium-sized molecules with rings
up to 12 atoms. This restriction hinders the study of large
conjugated systems like porphyrins and nanorings.
On the other hand, traditional Hilbert-space schemes are
free of the latter limitations but
can be unreliable for the large basis sets required in
modern computational chemistry. This
paper explores AIMs based on three robust Hilbert-space
partitions—meta-L ̈owdin, [1] Natural Atomic Orbitals
(NAO), [2] and Intrinsic Atomic Orbitals (IAO) [3]—which
combine
the advantages of real-space partitions without their

disadvantages. These partitions can effectively replace real-
space AIMs for evaluating the aromatic character.

For the first time, we report multicenter index (MCI) and
Iring values for large rings and
introduce ESIpy, an open-source Python code for
aromaticity analysis in large conjugated
rings. [4]
References
[1] Q. Sun, G. K.-L. Chan, J. Chem. Theory Comput., 2014,
10, 3784.
[2] A. E. Reed, R. B. Weinstock, F. Weinhold, J. Chem.
Phys., 1985, 83, 735.
[3] G. Knizia, J. Chem. Theory Comput., 2013, 9, 4834.
[4] J. Grèbol-Tomàs, E. Matito, P. Salvador, Chem. Eur. J.,
2024, e20241282.