[QE-users] Possibly too few bands at point 2 message in DFT+U+V calculation

[Lorenzo Paulatto]

> > In the HP output file, I am getting below two messages:
> > Possibly too few bands at point 2
> > If this is really related to QE input file then why I do not see any such message in QE output file?
>
> I am not totally sure but I presume that this might be related to the fact that you use too many cores for your system. I think no need to worry about this.

Hello Iurii, I hope you don't mind if I jump in and comment on this.
The premise is that the Sternheimer equation of DFPT can be solved using only the valence states, which is it greatest advantage w.r.t standard QM perturbation theory, which requires a sum over the entire spectrum of virtual states. In the case of metal, where electronic occupation can be fractionary, the Sternheimer equation can be adjusted to keep this into account (PRB 51, 6773 (1995)).
The completely empty states are still not required and the linear-response solver tries to throw them away to save time. The algorithm only includes states up to a ~3 sigmas (the smearing width) up from the Fermi energy. If during this search the algorithm runs out of bands before reaching the threshold, its warns that maybe there were not enough bands to begin with, i.e. that if there had been more bands their occupation may have been non-negligible.
The only way to be sure is to repeat the pw.x calculation increasing nbnd, but if pw.x did not complain during scf about the total integrated charge being slightly off, the calculation should be ok.

hth

Dr. Lorenzo Paulatto
IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université
phone: +33 (0)1 442 79822 / skype: paulatz
http://www.impmc.upmc.fr/~paulatto/ (https://link.getmailspring.com/link/30EFE2C7-FCF2-4279-A941-421485ED269D@getmailspring.com/0?redirect=http%3A%2F%2Fwww.impmc.upmc.fr%2F~paulatto%2F&recipient=dXNlcnNAbGlzdHMucXVhbnR1bS1lc3ByZXNzby5vcmc%3D) - https://anharmonic.github.io/ (https://link.getmailspring.com/link/30EFE2C7-FCF2-4279-A941-421485ED269D@getmailspring.com/1?redirect=https%3A%2F%2Fanharmonic.github.io%2F&recipient=dXNlcnNAbGlzdHMucXVhbnR1bS1lc3ByZXNzby5vcmc%3D)
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On Nov 25 2021, at 10:11 am, Iurii TIMROV via users <users at lists.quantum-espresso.org> wrote:
>
>
>
> > In the HP output file, I am getting below two messages:
> > Possibly too few bands at point 2
> > If this is really related to QE input file then why I do not see any such message in QE output file?
>
> I am not totally sure but I presume that this might be related to the fact that you use too many cores for your system. I think no need to worry about this.
>
> > Should we set nbnd in QE input file or we can ignore it?
>
> If you do not specify nbnd, pw.x will automatically include only occupied states for insulators and +20% more for metals.
>
> > Number of k-points >= 100: set verbosity='high' to print the bands.
> > I do not find q verbosity tag in "hp.x input description" file instead I found iverbosity.
>
>
> HP prints only irreducible q points if you use symmetry.
>
> > Anyway, it should not affect the final U+V value as we do not see any effect of verbosity on band structure calculation. RIght?
>
> Right
>
> > or I should set iverbosity=2 in HP input file?
>
> No need. But if you want to see more info you can do that.
>
> HTH
>
> Iurii
>
> --
> Dr. Iurii TIMROV
> Senior Research Scientist
>
> Theory and Simulation of Materials (THEOS)
> Swiss Federal Institute of Technology Lausanne (EPFL)
>
> CH-1015 Lausanne, Switzerland
> +41 21 69 34 881
>
> http://people.epfl.ch/265334 (https://link.getmailspring.com/link/30EFE2C7-FCF2-4279-A941-421485ED269D@getmailspring.com/2?redirect=http%3A%2F%2Fpeople.epfl.ch%2F265334&recipient=dXNlcnNAbGlzdHMucXVhbnR1bS1lc3ByZXNzby5vcmc%3D)
>
>
>
>
>
> From: users <users-bounces at lists.quantum-espresso.org> on behalf of Dr. K. C. Bhamu <kcbhamu85 at gmail.com>
> Sent: Thursday, November 25, 2021 3:47:50 AM
> To: Quantum Espresso users Forum
> Subject: [QE-users] Possibly too few bands at point 2 message in DFT+U+V calculation
>
>
> Dear Dr. Timrov,
>
> I have set verbosity = high in QE input file without specifying nbnd.
> In the HP output file, I am getting below two messages:
> Possibly too few bands at point 2
>
>
>
> If this is really related to QE input file then why I do not see any such message in QE output file?
> Should we set nbnd in QE input file or we can ignore it?
> Number of k-points >= 100: set verbosity='high' to print the bands.
>
>
>
> I do not find q verbosity tag in "hp.x input description" file instead I found iverbosity. Anyway, it should not affect the final U+V value as we do not see any effect of verbosity on band structure calculation. RIght? or I should set iverbosity=2 in HP input file?
>
> Thank you for guiding me.
>
> Regards
>
> K C Bhamu
> Postdoctoral Fellow
> School of Chemical Engineering
> University of Ulsan
> South Korea
>
>
>
>
>
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