The ABINIT Users Mailing List ( CLOSED )

[Xavier Gonze <gonze@pcpm.ucl.ac.be>]

Dear H Megchiche,

homegchiche@yahoo.fr wrote:
> Dear Abinit users, Actually, I'm doing the calculation of the vacancy 
> formation energy of nickel
> with the supercell method. I've choosed supercell with 8, 16, 27 and 32 
> sites. I would like to know
> how to choose the compatible brilouin zone sampling (the "ngkpt" input 
> variable) for each
> supercell. Thanks for your help and your time. Sincelly yours. H.megchiche

It is indeed possible to specify grids of k points that will be compatible, 
but
you will not succeed with only the ngkpt input variable : you will have to
use either the "kptrlatt" input variable , or complement ngkpt with several
shifts (nshiftk + shiftk) , or (likely the best) to generate automatically 
grids
(specified by kptrlatt and the shifts) with the same
resolution, using the "kptlen" input variable. See the description of this
latter input variable. There will be a direct relationship between the 
magnification
factor of your supercell, compared to the small Ni cell, and the magnification
factor of kptrlatt.

In any case, you should check with perfectly regular supercells (without 
vacancies)
that you get the "same" energy per atom, with these supercells and their 
associated
k-point grids. The only difference
should come from the exchange-correlation integration grid, and might be 
expected
to be on the order of 10 microHartree.

Good continuation,
Xavier GOnze