[Pw_forum] A problem about Ex.12

[Gabriele Sclauzero]

Dear mohsen modaresi,

Stefano de Gironcoli wrote:
> Dear mohsen modaresi
> 
>  you can describe an fcc crystal in an FCC bravais lattice with one atom 
> per cell or in a Simple Cubic cell with 4 atoms per cell or in a 
> tetragonal cell with 2 atoms per cell or in many other  equivalent ways.
> Why it is done using tetragonal lattice in that particular  example I 
> don't know but it may  be due  to  the need of  using some particular 
> orientation or orthonormal  Bravais vectors or some other reason.

What Stefano says is true. In that specific example, a tetragonal superell has been used 
in order to postprocess the charge density with pwcond.x and obtain the complex band 
structure of FCC Al along the (001) direction, as it is written in the README file which 
explains the example.
Since the pwcond code is built such that the transport direction has to be along z, you 
have to rotate your crystal according to the real desired transport direction.
Also notice that the basal plane of the supercell has to be orthogonal to this direction.

HTH

GS


> Hope this helps,
> 
> stefano. 
> 
> mohsen modaresi wrote:
>> Hi dear users
>> I read Ex.12 and run it, In the input file for Al (al.scf.in 
>> <http://al.scf.in> ) i see this part
>>      ibrav = 6,
>>     celldm(1) =5.3,
>>     celldm(3) =1.414,
>> But we konw that Al has F.CC structure, Why they set ibarav=6 not 2, I 
>> faced with this problem in example 11 in the Want package.
>> Thanks for answers
>>
>> Mohsen Modaresi
>> Msc. Student of Solid State Physics,
>> Department of Physics,Ferdowsi University of Mashhad,
>> Iran.
>>
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