[QE-users] definition of the hyperfine coupling constant in QE-GIPAW

[Gregor Mali]

Dear Davide,


I am studying several Cu(II)-based systems. One of them is Cu-L-alanine. Crystallographic unit cell of this complex comprises two Cu atoms and four L-alanine molecules. Hyperfine coupling constants on 13C nuclei calculated by QE-GIPAW were comparable to hyperfine coupling constants calculated by Orca, where the structural model used in Orca consisted of only one Cu atom and two L-alanine molecules.

The next system was one of metal-organic frameworks. Its unit cell, supplied to QE-GIPAW calculations, contained 12 Cu atoms, whereas the model used with Orca comprised 6 Cu atoms. The latter structural model described the same motif as was the one contained in the unit cell of periodic calculations. Nevertheless, hyperfine coupling constants on 13C nuclei obtained with QE-GIPAW were about 9-times as large as hyperfine coupling constants obtained with Orca:

Orca : QE-GIPAW

-0.9 :       -7.9
2.4 : 21.0
0.3 : 3.3

For another MOF system again a large factor was between the QE-GIPAW and Orca calculated constants.

Best regards
Gregor


________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Davide Ceresoli <davide.ceresoli at cnr.it>
Sent: Friday, December 18, 2020 12:44:29 PM
To: users at lists.quantum-espresso.org
Subject: Re: [QE-users] definition of the hyperfine coupling constant in QE-GIPAW

Dear Gregor,
     the hyperfine coupling should be multiplied by the number
of unpaired electrons (2*S_z). It also assumes I=1/2.

In the past I checked that GIPAW yields the same results of ORCA
and Gaussian for molecules in the case S = I = 1/2. I can re-check that.

Best.
Davide



On 12/18/20 10:22 AM, Gregor Mali wrote:
> Hello.
>
>
> Isotropic hyperfine coupling constants A_iso, calculated by QE-GIPAW, can differ
> by a large factor from A_iso, obtained by Orca. The factor depends on the number
> of unpaired electrons in the unit cell (used in QE) and in the cluster model
> (used in Orca). In Orca, A_iso is proportional to spin-density at the position
> of a nucleus divided by <S_z>. <S_z> is the maximum value of the z component.
> What is the definition of A_iso in QE-GIPAW? Is it perhaps proportional
> to spin-density multiplied by S(S+1)/<S_z>?
>
>
> Thanks in advance!
>
>
> Gregor Mali
>
> National Institute of Chemistry
>
> Ljubljana, Slovenia
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