[Pw_forum] super cell

[Gabriele Sclauzero]

Dear Vinicius,

   it is not clear to me if you want to build the primitive cell of Pt3Sn or a supercell. In the former case you may use a cubic cell (ibrav=1) and put a Sn in the origin and three Pt on the faces of the cube. If you want a supercell, well, it depends if you want to extend the structure along one direction only (hence you should use a tetragonal cell) or isotropically along the three directions (the supercell will still be cubic). I don't see any reason to use ibrav=0 to specify a tetragonal cell as you are doing in your input file. Moreover it is easy to see from your input that atoms 2 and 5 will overlap with the atom in the origin (and with each other) since their positions differ by a vector of Bravais lattice.

   It would be very kind of you if you take a few time to sign your future posts and specify your affiliation. Thanks!

Regards,

GS

Il giorno 10/ago/2010, alle ore 22.06, Vinícius Bertuzzo Lima ha scritto:

> Greetings!
> Before anything, thank you!
> 
> I'm trying to optimize a super-cell of Pt-Sn intermetallic, but when I determine the atomic positions of the crystal, there is overlapping of atoms, which determine the species as the source. 
> 
> For example, if I determine how the platinum atom (0,0,0), the whole basis of the crystal will, in its vertices of platinum atoms, as my only two intermetallic is Pt3Sn 
> vertices of the base would be two platinum and tin.
> 
> I understand the system, which would by ibrav = 0, but still is not working. How would an input on which to determine the position of only two atoms of the base and not the whole basis?
> 
> Down my input:
> 
> &CONTROL
>                  calculation = 'vc-relax' ,
>                 restart_mode = 'from_scratch' ,
>                       outdir = '/home/vinicius/tmp' ,
>                   pseudo_dir = '/home/vinicius/espresso-4.1.3/pseudo' ,
>  /
>  &SYSTEM
>                        ibrav = 0,
>                    celldm(1) = 7.10082033,
>                          nat = 5,
>                         ntyp = 2,
>                      ecutwfc = 30 ,
>                      ecutrho = 300 ,
>                  occupations = 'smearing' ,
>                      degauss = 0.05 ,
>                     smearing = 'methfessel-paxton' ,
>  /
>  &ELECTRONS
>                     conv_thr = 1.D-8 ,
>                  mixing_beta = 0.7D0 ,
>  /
>  &IONS
>                 ion_dynamics = 'bfgs' ,
>                    bfgs_ndim = 3 ,
>  /
>  &CELL
>                cell_dynamics = 'bfgs' ,
>                  cell_dofree = 'xyz' ,
>  /
> CELL_PARAMETERS cubic 
>      0.000000000    0.000000000    4.200000000 
>      0.000000000    1.000000000    0.000000000 
>      1.000000000    0.000000000    0.000000000 
> ATOMIC_SPECIES
>    Pt  195.08400  Pt.pw91-n-van.UPF 
>    Sn  118.71070  Sn.pw91-n-van.UPF 
> ATOMIC_POSITIONS alat 
>    Pt      0.000000000    0.000000000    0.000000000    0  0  0 
>    Sn      1.000000000    0.000000000    0.000000000    0  0  0 
>    Pt      0.500000000    0.500000000    0.707100000    0  0  0 
>    Pt      0.500000000    0.500000000   -0.707100000    0  0  0 
>    Sn      0.000000000    1.000000000    0.000000000    
> K_POINTS automatic 
>   4 4 1   0 0 0 
> 
> Thanks again. And have a great day! _______________________________________________
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§ Gabriele Sclauzero, EPFL SB ITP CSEA
   PH H2 462, Station 3, CH-1015 Lausanne

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