Multiwfn forum

saeed_E

Member

Registered: 2019-12-21

Posts: 158

Charge localization/delocalization

Dear Tian,

Is there any index (computation) by which one can prove charge(s) is really localized or delocalized over a given species (or a set of atoms in a species)? If so, could you please let me know instruction of computation?

I want to show charge (electron density) is much more localized in the separate reactants than that in the corresponding TS. While some concepts such as dipole moment and separation between charges could be used to show charges become more localized (delocalized) in going from separate reactants toward TS, I am interested in a much more specific index (characterization). For instance, in a SN2 reaction, charges become highly delocalized when TS is formed from separate ionic reactants. While this matter is quite evident in a SN2 reaction initialized with an anion and neutral reactant, this is not so obvious in a 13-DC reaction in which charge is more localized in the 1,3-dipole than in the TS where both reagents present and, thus an index needs to make the more degree of charge delocalization in the TS quite clear.

Sincerely yours,
Saeed

Last edited by saeed_E (2024-02-05 14:36:30)

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,639

Website

Re: Charge localization/delocalization

Dear Saeed,

In the case of SN2 involving net negative charge, I suggest first plotting Fukui function f- (corresponding to electron density difference between anion and neutral states) for reactant, TS and product, if you clearly observed that f- is much more delocalized at TS structure, then you can try to calculate spatial delocalization index (SDI) for grid data of f- via Multiwfn for the three structures to quantify the difference in delocalization extent of the extra electron, see Section 3.200.19 of latest version of Multiwfn manual and Section 4.200.19 for examples.

Best regards,

Tian

saeed_E

Member

Registered: 2019-12-21

Posts: 158

Re: Charge localization/delocalization

Dear Tian,
Too many thanks for your highly informative and valuable guidance.
I will do as you recommended and, if you kindly let me, I would contact you if any problems (questions) are encountered.

Sincerely,
Saeed