[Pw_forum] graphite cell optimization failed

[Cyrille Barreteau]

Dear Eric

I am not a specialist of Carbon but from what I have read (and heard)
the interaction between two graphene layers is of Van der Waals nature.
Therefore standard DFT is not very good. It seems that LDA is doing
better than GGA with this respect. You could also try to include the
semi-empirical dispersion term (proposed by Grimme) and now implemented
if pwscf..

good luck

  cyrille

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On Wed, 2011-03-23 at 12:33 -0400, Eric Germaneau wrote:
> Dear all,
> 
> I'm trying to optimize unit cell parameter of graphite.
> The problem is the c axis gets too long.
> Starting from published data my initial parameters are a=4.59203 Bohr
> and c=12.513 Bohr.
> The final values are 4.664 and 15.829 respectively.
> I need someone to explain to me what I did wrong, I've attached my
> input file.
> That's a basic calculation so it's very frustrating to not make it
> done.
> I thank you in advance,
> 
>                                     Eric.
> 
> -- 
>               Be the change you wish to see in the world
>                           — Mahatma Gandhi —
> 
>                           Dr. Éric Germaneau
> 
>                      College of Physical Sciences
>           Graduate University of Chinese Academy of Sciences
>                            Yuquan Road 19A
>                             Beijing 100049
>                                 China
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