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sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,625

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How to Quantify CH----Pi Interactions using Multiwfn?

Today a Multiwfn user asked me how to quantity CH...pi interaction using Multiwfn, my reply is pasted below, which may be also useful for other users.

I don't know how do you want to quanity the CH...pi interaction. If you want to predict its strength, unfortunately there is no general way. However, if you hope to compare relative strength between CH...pi interactions in different systems, the following quantities may be worth to consider:
(1) Integral of electron density (or other functions) within RDG isosurface of CH...pi. This can be realized by domain analysis, see Section 4.200.14.1 of Multiwfn manual for example.
(2) Sum of IBSIW indices between H of CH group and all carbon atoms in the aromatic ring. See Section 3.23.6 of Multiwfn manual about this index. The larger the sum, the stronger the interaction is expected.
(3) Penetration distance between vdW surfaces of the C-H moiety and the aromatic ring. This point has been mentioned in Section 4.A.5 of multiwfn manual. The deeper the penetration, the stronger the interaction is expected.
(4) Electrostatic potential minimum value over local vdW surface of the aromatic ring moiety, and electrostatic potential maximum value over hydrogen of the CH group. The more negative the former and the more positive the latter, the stronger the interaction is expected. See Section 4.12 of Multiwfn manual for example on how to obtain extrema of electrostatic potential on vdW surface.