input variables

External optional components of Abinit (BigDFT, Wannier90, ...) and codes using / providing data from / to Abinit (AtomPAW, EXC, DP, SAX, WanT, Yambo, ...).

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saikrishna
Posts: 15
Joined: Fri Jun 21, 2019 12:11 pm

input variables

Post by saikrishna » Fri Jun 21, 2019 12:19 pm

Hi all
I am new to ABINIT and am learning it. I have a doubt in the usage of variables ngkpt, nkpt and thier consequences and I am asking this in the context of base 3_4 tutorial.

Thanks in advance,
Sai krishna

ebousquet
Posts: 370
Joined: Tue Apr 19, 2011 11:13 am
Location: University of Liege, Belgium

Re: input variables

Post by ebousquet » Fri Jun 28, 2019 6:59 pm

Dear Sai krishna,
nkpt is the total number of k-points and ngkpt is used in the calculation while to set the number of k-point in each direction ngkpt is used. Usually ngkpt is used in the input and nkpt is automatically calculated depending on the symmetries of the system and it is better to let the code calculating it.
Best wishes,
Eric

saikrishna
Posts: 15
Joined: Fri Jun 21, 2019 12:11 pm

Re: input variables

Post by saikrishna » Thu Jul 04, 2019 12:23 pm

Hi Eric
Thank you for the answer but I have doubt in how is k points generated from the ngkpt and how is nkpt calculated?

Thanks in advance
Sai krishna.

ebousquet
Posts: 370
Joined: Tue Apr 19, 2011 11:13 am
Location: University of Liege, Belgium

Re: input variables

Post by ebousquet » Fri Jul 12, 2019 4:30 pm

Dear Sai krishna,
nkpt is calculated by taking into account the symmetry of the crystal (if with kptopt=1) such that nkpt will be the number of inequivalent k-points to reduce the size of the calculation.
Best wishes,
Eric

saikrishna
Posts: 15
Joined: Fri Jun 21, 2019 12:11 pm

Re: input variables

Post by saikrishna » Fri Aug 16, 2019 11:57 am

Hey Eric
I have understood your answer and can you tell the role of shiftk?
Thanks in advance
Sai krishna

NPike
Posts: 34
Joined: Fri Mar 18, 2016 1:15 pm

Re: input variables

Post by NPike » Mon Oct 21, 2019 3:08 pm

Hello,

The variable shiftk is used to shift the k-point grid by a fixed amount after Abinit determines the list of irreducible k-points. For most calculations, one can safely set shiftk = 0 0 0 and nshiftk = 0.

See https://docs.abinit.org/variables/basic/#shiftk for additional information and some examples.

-Nick
Nicholas A. Pike
Research Scientist

Olivier.5590
Posts: 6
Joined: Fri Nov 29, 2019 5:01 pm

Re: input variables

Post by Olivier.5590 » Sat Nov 30, 2019 3:21 pm

Yeah, sometimes you want to calculate based on a grid point that isn't zeroed, and like that, you don't have to try to calculate stuff approximatively when compensating for another starting point.

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