[Pw_forum] inconsistent quadrupolar coupling from gipaw calculation

[Davide Ceresoli]

Dear Jia,
     I have to admit that this is the first time that NMR/EFG results
depend so much on the choice of the pseudopotential. I've calculated
a bunch of minerals, both with NC and US pseudos, and results are
in good agreement each other.

I've tested several Co pseudos (NC, NC+semicore, PAW+semicore) on
Co3O4 spinel and the EFG results span the entire real numbers range,
both for Co and for O.

Which one is correct? I don't know. I'm in favor of pseudopotentials
with semicore states. They should be closer to all-electron.

Do you have some reference with Co EFG calculated all-electron (wien2k,
elk/exciting) on some simple system? If not, is there someone that
could help us to setup a wien2k/elk calculation?

Best regards,
     Davide





On 09/20/2017 06:50 PM, Jia Chen wrote:
> Dear All,
> 
> I am working on calculating nmr parameters with gipaw code. I have two settings: 
> one with norm-conserving gipaw pesudopotentials which has some semi-core states, 
> and the other with ultra-soft gipaw pseudopotentials. Electronic structure 
> eigenvalues from pwscf look similar, and chemical-shift are not far away from 
> each other. The issue is quadrupolar coupling, for Co, norm-conserving 
> calculation gives 0.5MHz and ultra-soft gives 1.5MHz. It seems to me a 
> significant discrepancy.  I don't know what caused the inconsistency, and which 
> one is more reliable. I appreciate any insight on this problem.
> 
> One thing about norm-conserving calculation is that the code gives warming about 
> some orbitals has zero norm. I don't know if that could be of concern.
> 
> Cheers
> Jia