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[ren <opticalcase@gmail.com>]

Hi Dr Caliste, thank you very much!!!! I will take note of it!!!!

Cheers,
Yee Yan

On Fri, Feb 27, 2009 at 8:26 PM, Damien Caliste <damien.caliste@cea.fr> wrote:
> Hello,
>
> Le 27/02/2009, ren <opticalcase@gmail.com> a écrit :
>> what you are saying, is that for my calculation of a 2x2x2 supercell,
>> i will get the same result as a 1x1x1 unit cell
> Yes, but take care of the k points. The total energy of a 1x1x1
> supercell is indeed one eightth of the energy of a 2x2x2 supercell if
> the k point mesh in the 1x1x1 supercell is twice denser in the three
> directions.
>
> This is due to the fact that in a 2x2x2 box, you allow your system to
> have plane waves with a maximum period twice the one they can have in a
> 1x1x1 supercell. So in the 1x1x1 you have to add k points to allow the
> computation of the long period plane waves and thus have the same basis
> set to compare total energy.
>
> Damien.
>
>