[Pw_forum] Atomic positions

[Pietro Delugas]

Dear Artur


your system contains one atom per unit-cell, if you want to describe 
the  same  system using a super-cell which containing   8 atoms.

You have to:

- double your lattice constant celldm(1)  from 7.5 to 15;

- set to 8 the number of atoms (nat)

-  set to 2 the number of types  (ntyp)

-  set the 8 atomic positions ( cartesian coordinates using alat units  
) to

Al 0 0 0

Al 0.5 0 0

Al 0. 0.5 0.0

Al 0.0 0.0 0.5

Al 0.5 0.5  0.0

Al  0.5 0.0 0. 5

Al 0.0 0.5 0.0

Al 0.5 0.5 0.5

  and then you can change any of the 8 Al to Si and you are done

regards Pietro


On 13/11/2016 16:56, adurajski at wip.pcz.pl wrote:
> Dear All,
>
> I have a simple cubic structure (8 atoms at corners), for example:
>
> &system
>      ibrav= 0, celldm(1) =7.50, nat=  1, ntyp= 1
>   /
> CELL_PARAMETERS {alat}
>    1.000000000000000   0.000000000000000   0.000000000000000
>    0.000000000000000   1.000000000000000   0.000000000000000
>    0.000000000000000   0.000000000000000   1.000000000000000
> ATOMIC_SPECIES
>   Al  26.98 Al.pz-vbc.UPF
> ATOMIC_POSITIONS
>   Al 0.00 0.00 0.00
>
> Is it possible to change only one atom in this system, for example I would
> like to replace Al by Si at one corner and leave remaining 7 corners
> occupied by Al?
>
> Best Regards,
> Artur