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[Stephane BECU <stephane.becu@st.com>]

Dear all,

I'd like to calculate the dielectric tensor of orthorhombic Ta2O5 and I need
to know its number of valence bands. Does someone know the number of valence
bands in defect-free Ta2O5?

Thanks for the help,

Stéphane Bécu
-----Original Message-----
From: stephane becu [mailto:stephane.becu@st.com] 
Sent: Thursday, March 16, 2006 1:26 PM
To: 'forum@abinit.org'
Subject: [abinit-forum] Vacancies implementation in Al2O3


Thaks Vincenzo for yoour help,

Actually I know this article but I did not manage to understand why the
authors wrote 7 Al and 9 O positions in Table I. Why 7 Al and 9 O? Can you
tell me more?

Thanks again

Stéphane

-----Original Message-----
From: Vincenzo Fiorentini [mailto:vincenzo.fiorentini@gmail.com] On Behalf
Of Vincenzo Fiorentini
Sent: Thursday, March 16, 2006 1:10 PM
To: forum@abinit.org
Subject: Re: [abinit-forum] Vacancies implementation in Al2O3


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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