[QE-users] Crystallographic group determination

[José Carlos Conesa]

Hi,

I'm not sure to understand your question, but if what you mean is that 
the primitive cell of Ga2O3 has all angles different from 90º, this is 
the normal situation for any monoclinic centered lattice. In fact there 
is still symmetry there; you will see that two of the primitive unit 
cell length parameters coincide, as well as two of the angles. This is 
due to the presence of a symmetry plane.

Besides this, you should note that even a fully triclinic cell is not 
necessarily of space group P1; it might be also group P-1 (group number 
2) if it has an inversion center of symmetry.

All the best,

JC Conesa

El 01/04/2019 a las 4:18, Ankit Sharma escribió:
> Hi,
> Thank you very much for the reply Dr. Conesa.
> As a follow up question, is it a convention to represent the symmetry 
> of the primitive unit cell as that of the conventional cell because by 
> looking at the crystal structure of the primitive unit cell for the 
> above mentioned system i.e Gallium Oxide, it appears to be triclinic 
> and hence the P1 symmetry.
>
> Thank You,
> Ankit Sharma
> University at Buffalo
>
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>
> On Sun, Mar 31, 2019 at 12:55 PM Ankit Sharma <ankitub31 at gmail.com 
> <mailto:ankitub31 at gmail.com>> wrote:
>
>     Hi,
>     I am working with Gallium Oxide which has a 20 atom conventional
>     cell with the space group of *C2/m *and a 10 atom primitive cell
>     with space group of *P1 *(materials project):
>     https://materialsproject.org/materials/mp-886/#.
>
>     When I run scf calculations on conventional cell the output
>     clearly states as *C2/m *symmetry, but for the primitive cell too,
>     the output is again *C2/m*.
>     I am unable to figure out the reason for it. Am I missing
>     something? Any help in this regard will be greatly appreciated.
>     Attached is the cif file from the materials project for reference
>     for both the conventional and the primitive unit cells and the
>     input and output files for the fake run to determine the symmetry.
>
>     Thank You,
>     Ankit Sharma
>     University at Buffalo
>
>
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-- 
José C. Conesa
Instituto de Catálisis y Petroleoquímica, CSIC
Marie Curie 2, Madrid, Spain
www.icp.csic.es
Tel. (+34)915854766

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