[Pw_forum] Is the Graphite surface flate?

[Gabriele Sclauzero]

On 07/05/2010 08:19 PM, Masoud Nahali wrote:
> Dear Quantum Espresso users
>
> I optimized the graphite bulk and the layers were completely flat. But 
> when I try to "relax" the graphite surface (slab 2*2 with 3 monolayer) 
> with 10 angstrom vacuum all the layers become extremely ripple!!! I 
> can not find the problem. May it related to the number of layers? 
> anyhow the number of layers is like the bulk. Your help would be a 
> great gift.
> __
Are you using the experimental or the theoretical value for the in-plane 
(graphene) C-C distance? I guess that the PBE value is larger than the 
experimental one, so that if you start from the experimental C-C 
distance in the graphene layer and let everything relax, then the atoms 
would like to go towards the theoretical equilibrium distance and this 
may cause the rippled structure.
Secondly, I don't know if you can pretend that the innermost layer is 
graphite bulk-like, having only three layers in total.


HTH

GS

-- 

Gabriele Sclauzero, EPFL SB ITP CSEA
PH H2 462, Station 3, CH-1015 Lausanne

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