[Pw_forum] thin film construction

[dev sharma]

Dear Sir,
 Like i want to make films of ZnO, then should i make a 2*2*2 supercell of
ZnO and put vacuum in between two layers ???  It means we are using two mono
layers seprated by vacuum ??? and Sir, how we will put vaccum between two
layers means which inputs to study    ? Sir ZnO is ibrav=4, and if i will
put vacuum between supercell will the ibrav=4 not change ???   Is there any
example/material to study related or any such problem in forum ??
Thanks ,
With regards,
Dev Sharma,
Univeristy of Delhi

On Wed, Sep 16, 2009 at 11:22 PM, Stefano Baroni <baroni at sissa.it> wrote:

>
> On Sep 16, 2009, at 7:34 PM, dev sharma wrote:
>
> hi 2 all,
>
> I am somewhat confused about construction of a film. like whenever we
> calculate the band gap of a unit cell of any system and 2*2*2 supercell  of
> that system we get the same value whereas when one moves from nano regime to
> larger scale the band gap should decrease. It means that the unit cell is
> treated as crystal.So, if i construct a film , by taking it as 2*2*1
> supercell, it will again consider it as sum of crystals and will yield the
> same results ?????  Hope so that my question is clear ..
>
>
> Not to me ...
>
> How to make a structure of  film ???
>
>
> using supercells "intercalated" with vacuum, the same way you would to
> simulate a surface. Only, in this case the thickness of the slab is not an
> artifact of the model, but corresponds to the physical thickness of the film
> (if the film is thin enough to be simulated with a supercell)
>
> SB
>
> Thanks in advance.
> With regards,
> Dev Sharma
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> ---
> Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
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