Multiwfn forum

alessiomacorano

Member

Registered: 2023-12-19

Posts: 17

Aromaticity index calculation

Dear Prof. Tian Lu,

First of all, thank you very much for your outstanding work on MULTIWFN and for managing the forum.

I have two quick questions:

1) In your opinion, what are the most appropriate aromaticity indices for studying π-interactions in benzene dimers? 

(The example geometries are the three shown in the image)

2) If I wanted to study the aromaticity of a single benzene ring, which indices would you recommend?

I ask because HOMA and the Bird index come to mind, but perhaps they aren’t sufficient.

Thank you so much for your Help!

My best

Alessio

sobereva

Tian Lu (Multiwfn developer)

From: Athens, Greece

Registered: 2017-09-11

Posts: 2,229

Website

Re: Aromaticity index calculation

Dear Alessio,

1 Aromaticity index is not directly related to pi-pi interaction in benzene dimers. Weak interactions usually have negligible influence on electronic structure and thus aromaticity. To study this the pi-pi interaction, there are many analyses in Multiwfn can be used, such as IGMH visualization analysis (DOI: 10.1002/jcc.26812, DOI: 10.1002/anie.202504895, DOI: 10.1016/B978-0-12-821978-2.00076-3), sobEDA energy decomposition (DOI: 10.1021/acs.jpca.3c04374), superposition of electrostatic potential colored vdW surface maps of monomers (Section 4.A.13 of Multiwfn manual), etc. Please check Section 4.A.5 of Multiwfn manual, which is an overview of methods for studying weak interactions.

By the way, I have a very detailed blog article to discuss pi-pi interaction: http://sobereva.com/737

2 It is relatively easy to characterize aromaticity of benzene in different environments, the HOMA you mentioned can be used, however, its variant HOMAc (J. Org. Chem., 90, 1297 (2025)) performs better and is also supported in Multiwfn, see Section 3.28.7 of manual. In addition, I suggest also using at least one aromaticity descriptor defined based on electronic structure to study aromaticity, the multicenter bond order (MCBO) in Multiwfn is a preferential choice, see Section 3.11.2.

Best regards,

Tian

alessiomacorano

Member

Registered: 2023-12-19

Posts: 17

Re: Aromaticity index calculation

Dear Prof Tian Lu,

Simply Amazing!! thank you so much for your detailed response !!

My best

Alessio