[Pw_forum] A problem about Ex.12

Stefano de Gironcoli degironc at sissa.it
Thu Nov 26 16:26:42 CET 2009

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.
Hope this helps,


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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