[QE-users] Different implementations of the Hubbard 'U' between QE and VASP

[Nicola Marzari]

On 06/05/2020 22:02, Shivesh Sivakumar wrote:
> Nicola,
> 
> Sorry to bring up the subject again but I still can't reconcile 
> something. I understand that 'U' is not universal and not completely 
> portable between different PPs. But what I find odd is the effect of 
> 'U'. On QE (with NCPP), 'U' seems to suppress the band gap whereas in 
> VASP (with PAW), 'U' seems to widen the band gap. This is what looked 
> very strange.
> 
> Best,
> Shivesh

Not sure what to say - i.e. one would really need to delve deep into the 
case study. I think the VASP PAW projectors that are used for the U are 
strictly localized inside the core, and so might be quite a bit 
different from those of say a NCPP pseudo. But this is the kind of 
question that can be answered only by a detailed study - do you get with 
no U the same results?

Where did you get the Cr norm-conserving pseudo? Is it any good?
Our recommendation is the USSP from the GBRV work of David Vanderbilt:
https://www.materialscloud.org/discover/sssp/plot/precision/Cr

			nicola


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Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
Director, National Centre for Competence in Research NCCR MARVEL, EPFL
http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project