[Pw_forum] ibrav7 doesn't show the structure of BaNi2As2 correctly

[Giovanni Pizzi]

Dear David,
I think that the relative (crystal) coordinates that you write for the 
5-atom cell are still expressed in terms of the conventional cell (the 
one with vectors (a,0,0), (0,a,0), (0,0,c). This is the cell used in the 
case ibrav=14, reason for which you get the correct structure.

Instead, the cell used in ibrav=7 is the primitive one - the docs say:

v1=(a/2)(1,-1,c/a),  v2=(a/2)(1,1,c/a),  v3=(a/2)(-1,-1,c/a)

Therefore you have to express the relative (crystal) coordinates with 
respect to this basis set, and not in terms of the lattice vectors of 
the conventional cell.

Best,

Giovanni Pizzi



On 05/27/2014 03:48 PM, David Foster wrote:
> Dear users
>
> The atomic positions for BaNi2As2 crystal with space group of I4/mmm (139) are:
>
> Ba (2a): 0, 0,   0
> As (4e): 0, 0,   0.3471
> Ni(4d):   0, 0.5, 0.25
>
> I used MS Visualizer to build the conventional tetragonal cell (a = b = 4.1474  c = 11.619).
>
> After seeing the structure with MS, I convert it to primitive and finding all atoms positions. Only 5 atoms there are in primitive (If I am right):
>
> Ba 0.000000 0.000000  0.000000
> As 0.347100 0.347100  0.000000
> As 0.652900 0.652900  0.000000
> Ni 0.750000 0.250000  0.500000
> Ni 0.250000 0.750000  0.500000
>
> I prepared two input file for QE5.0.3, one with ibrav=7 and 5 atoms, and the other with ibrav=14 and all atoms in conventional cell instead of its primitive:
> with P1 symmetry, the cell has 10 atoms:
> Ba 0.0000 0.0000  0.0000
> Ba 0.5000 0.5000  0.5000
> As 0.000 0.000  0.3471
> As 0.5000 0.5000  0.8471
> As 0.000 0.000  0.6529
> As 0.5000 0.5000  0.1529
> Ni 0.000 0.5000  0.25000
> Ni 0.500 0.0000  0.250000
> Ni 0.000 0.5000  0.75000
> Ni 0.500 0.0000  0.750000
>
> I have attached two inputs and two pictures that xcrysden shows. While ibrav=14 shows the crystal correctly, ibrav=7 has a problem and doesn't show the crystal properly. I am confused!!
> Any help will be appreciated.
>
>
>
> Then, I
>   
> Regards
>
> David Foster
>
> Ph.D. Student of Chemistry
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum


-- 
Giovanni Pizzi
Post-doctoral Research Scientist
EPFL STI IMX THEOS
MXC 340 (Bâtiment MXC)
Station 12
CH-1015 Lausanne (Switzerland)
Phone: +41 21 69 31124

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20140527/f6c72c02/attachment.html>