[Pw_forum] IFCs and Difference between unit cell and supercell

Lorenzo Paulatto lorenzo.paulatto at impmc.upmc.fr
Sat Oct 20 13:30:18 CEST 2012

On 20 October 2012 12:59, karan deep <karandeepster at gmail.com> wrote:

> >in order to get exactly the same number, you have to use either
> >a converged grid of k-points, or exactly the same k-points.
> i try the example 2 of silicon which has 10 k-points mentioned in it for
> both sc and fcc.
> any suggestions please

"exactly the same k points" does not mean "copy and paste the list of
points". You have to reduce the list for the unit cell to a certain subset
according to the cell->supercell mapping of the Brillouin zone.

I.e. the Gamma point in the SC cell becomes Gamma (weight 1/4) + X =a/2pi(1
0 0) (weight 3/4) in the FCC cell. In general it is not easy, you will need
to think some time (let's say a few hours) about it.


Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Université Paris 6
phone: +33 (0)1 44275 084 / skype: paulatz
www:   http://www-int.impmc.upmc.fr/~paulatto/
mail:  23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05
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