Multiwfn forum

rodrigocormanich

Member

Registered: 2025-02-21

Posts: 4

CVB Index

Dear Professor Tian Lu,

I have seen in Multiwfn manual that CVB indexes are calculated as:

"In my viewpoint, the best definition of ELF(C-V) should be the ELF value at the minimum dissecting core and valence shell of donor atom on the ELF curve between D and H"

However, in Theor. Chem. Acc., 104, 13 (2000) it is said the following:

"In order to build up a scale for the weak and medium hydrogen bonds based on topological criteria we define the core±valence bifurcation (CVB) indices as the difference of n(rcv), the lowest value of the ELF for which all the core basins of the complex are separated from the valence, and n(rAHB), the value at the saddle connection of the V(A, H) and V(B) basins."

So it seems that it should be used the "lowest value of the ELF for which all the core basins of the complex are separated from the valence" instead of the minimum dissecting the core and valence of donor atom.
For instance, in this ELF plot they use the ELF "peak" marked in red below as the lowest one separating core from valence:

That is why, the authors use different ELF references in different papers, as pointed out in the manual:

"However, in the subsequent paper Struct. Chem., 16, 203 (2005) written by the same author, I found the ELF(C-V) is seemingly calculated as 375 3  Functions the ELF value at one of exactly located ELF bifurcation points connecting core and valence basin of donor atom (while acceptor atom is seemingly ignored)."

So, the automatic CVBI calculation in Multiwfn should not be changed to calculate considering the lowest value of the ELF for which all the core basins of the complex are separated from the valence instead?

Thank you very much in advance

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,927

Website

Re: CVB Index

In my opinion, if the CVB index is used to measure H-bond strength, "lowest value of the ELF for which all the core basins of the complex are separated from the valence" may not be the most reasonable way of defining ELF(C-V), because the role of donor atom and that of acceptor atom is very different in a H-bond, not only the hydrogen involved in the H-bond is bonded to the donor, but also ELF(DH-A) fully distinguishes donor and acceptor. Correspondingly, the ELF(C-V) should be an exclusive property of the donor side, and hence it is explicitly referred to as ELF(C-V,D) in the output of CVB index calculation function of Multiwfn.

Although the implementation of CVB index in Multiwfn is not exactly in line with the authors' original defintion for some systems, I think it is the most logically acceptable.