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saeed_E

Member

Registered: 2019-12-21

Posts: 292

Sigme- or Pi-hole characterization with Laplacian of Rho

Dear Tian,
I hope you are doing well. Please, if possible, kindly let me ask you a question about Sigme- or Pi-hole characterization with the Laplacian of Rho.
Is it true to state that "a sigma-hole or a pi-hole is always characterized with the emergence of a hole on the isosurface of the Laplacian of Rho when an isovalue of zero is considered"?

In advance, thank you very much.

Sincerely,
Saeed

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,954

Website

Re: Sigme- or Pi-hole characterization with Laplacian of Rho

Dear Saeed,

I think it is true.

Best,

Tian

saeed_E

Member

Registered: 2019-12-21

Posts: 292

Re: Sigme- or Pi-hole characterization with Laplacian of Rho

Dear Tian,
Many thanks for your kind attention and, for guiding me with your highly valuable confirmation.

Please, also, let me ask one more question. In some cases, such as for TeHF compound in which the presence of a sigma-hole along the extension of the Te-F bond is expected, drawing isosurface of Laplacian of Rho (with isovalue= 0, namely the reactive surface) does not show a hole. On the other hand, this sigma-hole can be seen when isovalue is increased to 0.001 (a value slightly greater than zero). Could you please let me know why?

As another case, SnH3F could be mentioned. For this compound, the emergence of an expected hole along the Sn-F bond can never be satisfied using ANY value as isosurface for Laplacian of Rho. Such cases made me quite confused. Please let me know why some cases fail to present an expected sigma-hole over the Laplacian isosurface. I tried several times to attach "SnH3F.fch" file generated at M06-2X-D3(0)/def2-TZVPP level but, all tries failed! Using Multiwfn and VMD, I could not see the sigma-hole in this compound at any isovalue of Laplacian of Rho!

Sincerely,
Saeed

Last edited by saeed_E (2025-03-22 20:31:16)

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,954

Website

Re: Sigme- or Pi-hole characterization with Laplacian of Rho

Dear Saeed,

I suggest try to use ELF or LOL isosurface.

To represent hole by isosurface of Laplacian of rho, the precondition is that Laplacian of rho is able to exhibit the region where electron density concentrates (e.g. lone pair and covalently bonding regions), but it often fails for elements with large atomic radius, such as Sn.

Best,

Tian

saeed_E

Member

Registered: 2019-12-21

Posts: 292

Re: Sigme- or Pi-hole characterization with Laplacian of Rho

Dear Tian,
Too many thanks for your kind attention and the highly valuable, informative, and professional suggestion.

Sincerely yours,
Saeed