k-point mesh for HF type calculations and the IBZKPT_HF subroutine

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elsilva
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k-point mesh for HF type calculations and the IBZKPT_HF subroutine

#1 Post by elsilva » Sun Mar 06, 2011 1:05 pm

Hello,

I'm starting to do hybrid calculations by using the HSE06 functional implemented in VASP 5.2.8 07. My unit cell is a 40 atom structure BCC lattice, which I define in the POSCAR file (just as in the normal GGA-PBE runs to generate the respective WAVECAR file).

Accordingly to your manual on how to do less expensive HF calculations one can use a manual k-point settings in the BZ: such as the BCC or FCC -like lattice defined in the KPOINT file. In order to perform a DOS calculation, and using the tetrahedron method with Blöchl corrections smearing, I need at least 4 k-points in the BZ. So, in order to follow the given suggestion I need to use a fcc-like lattice in the BZ (because the bcc-like configuration results only in 2 k-points).

When doing so, I (obviously) get the following error message
VERY BAD NEWS! internal error in subroutine IBZKPT:
Reciprocal lattice and k-lattice belong to different class of lattices. Often results are still useful... 4

Should I be worried about this message - or may I ignore it as just a warning about the different lattice settings - bcc for the reciprocal space and fcc for the BZ? Using this procedure it really speeds up the calculation time...

When performing the same calculations on a conventional cell, of the same material, using a 80 atom cubic structure, the warning disappears. I think its because the fcc lattice belongs to the cubic structure and VASP hence doesn't complain?

Another thing that I've noticed - when using an automatic Monkhorst-Pack or Gamma centered mesh the k-points generated in the 1st BZ by a GGA-PBE run is different than with a hybrid run returned by the IBZKPT_HF subroutine (generally it gives more k-points for the HSE06 run). Can anyone explain me why?

Thank-you
EL !alien
Last edited by elsilva on Sun Mar 06, 2011 1:05 pm, edited 1 time in total.

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Re: k-point mesh for HF type calculations and the IBZKPT_HF subroutine

#2 Post by support_vasp » Tue Sep 10, 2024 2:11 pm

Hi,

We're sorry that we didn’t answer your question. This does not live up to the quality of support that we aim to provide. The team has since expanded. If we can still help with your problem, please ask again in a new post, linking to this one, and we will answer as quickly as possible.

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