ABINIT Discussion Forums

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

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

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.

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

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

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

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.