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[Vincenzo Fiorentini <vincenzo.fiorentini@dsf.unica.it>]

there is a good paper on the topic:
Pinto et al., prb 70, 125402 (2004).
the cell is 40 atoms. I estimated a
diagonal dielectric constant (9,9,11).

V. Fiorentini


On 16 Mar 2006, at 11:48 AM, Pierre Boulenc wrote:

> Dear Stephane,
>
> How big is your supercell for gamma-Al2O3?
> Starting with the cubic spinel unit cell (which has 16 * 83.33 %  
> octahedral Al, 8 tetrahedral Al and 32 O atoms), you need at least  
> 3 unit cells to have 8 vacancies in your whole supercell. That  
> would bring you up to 160 atoms in your supercell.
> I think that's quite a lot, and if you plan to calculate dielectric  
> properties, you will need well-enough converged results which may  
> take a huge time for such a number of atoms.
>
> Regards,
>
> Pierre
>
>
> Stephane BECU a écrit :
>
> > Dear abinit users,
> >
> > I try to build a supercell for calculating dielectric properties  
> > of gamma-Al2O3. I begin with an ideal spinel unit, typified by  
> > MgAl2O4. Then I do some modification of this ideal unit, one of it  
> > is to remove two Al atoms to create two vacancies. The thing is I  
> > do not know how to declare the vacancies:
> > --> do I have to count them like the other atoms in natom?
> > --> what type (typat) of atoms do I have to define?
> > --> how define their positions?
> >
> > Thanks for your help,
> >
> > Stéphane Bécu
>
> --
>
> Pierre Boulenc
>
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