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PedroSilva

Member

Registered: 2022-09-30

Posts: 2

A strange result in Atomic dipole moment corrected Hirshfeld charges

I have been analyzing some results on systems composed of two fragments:
1) an alkyne of the form CH3-C(triple-bond)C-X   (where X is NH2, CH3, CH3, OCH3 or SCH3) 
2) [Cu(CH3)2] -

The ADCH charges computed for the pi-complexes and reaction intermediates look very reasonable, but for the pre-reactional complexes (composed of the two intact fragments at around 3.2 to 4 angstrom of each other)  I get very large charges on the Cu (from -3.5 to +9.5) and very large  charges on the methyl carbons attached to the Cu (the total charge of the Cu(CH3)2- moiety does remain reasonable, at -0.9) . The charges on the alkyne moiety look reasonable. At first I assumed  this strange behavior might be due to the large electric dipole of the [Cu(CH3)2]- moiety , but I now know it must be something else because this strange behavior does not happen when X is NH2 or PH2, only when X=CH3, OCH3, or SCH3 , or when I compute the isolated [Cu(CH3)2] - even though the [Cu(CH3)2]- moiety where the "error" (?) appears  has the same geometry in all cases.

This unfortunately makes me a little wary of using this method for my other comparisons.

Has anyone here found such behavior in other systems?

Last edited by PedroSilva (2022-09-30 11:24:28)

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,830

Website

Re: A strange result in Atomic dipole moment corrected Hirshfeld charges

Please try to use Multiwfn to calculate Hirshfeld-I or CM5 charges, they are usually comparably reasonable as ADCH. In very rare cases, I noticed that the current algorithm for calculating correction charges of ADCH is not quite numerically stable. If Hirshfeld-I or CM5 works in the present case, you can use them instead.

PedroSilva

Member

Registered: 2022-09-30

Posts: 2

Re: A strange result in Atomic dipole moment corrected Hirshfeld charges

Yes, I have meanwhile computed CM5 charges, and they look completely reasonable.

PS: in case this might be important for the diagnosis of the origin of the error,  my computations had an ECP on  Cu  (SBKJC) and  6-311G(2d,p) on the other atoms

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,830

Website

Re: A strange result in Atomic dipole moment corrected Hirshfeld charges

This problem is irrelevant to basis set, but mostly related to spatial arrangement of atoms in special configuration.