[Pw_forum] ibrav=2 and space_group=202: input coordinate misunderstood

[Musil Félix]

Thank you very much for your answers, I now understand how QE interprets the input in this case and solved my problem.
Best regards,

Felix


Félix Musil
Doctoral Assistant - Ph.D Student

EPFL STI IMX COSMO
LABORATORY OF COMPUTATIONAL SCIENCE AND MODELLING
Institute of Materials Science and Engineering
MXG 319
Station 12
CH-1015 Lausanne
Switzerland

E-mail: felix.musil at epfl.ch
http://cosmo.epfl.ch/

________________________________________
De : pw_forum-bounces at pwscf.org <pw_forum-bounces at pwscf.org> de la part de Tone Kokalj <tone.kokalj at ijs.si>
Envoyé : samedi 16 septembre 2017 09:00
À : pw_forum at pwscf.org
Objet : Re: [Pw_forum] ibrav=2 and space_group=202: input       coordinate      misunderstood

On Fri, 2017-09-15 at 20:22 +0000, Musil Félix wrote:
> Dear Paolo,
>
> I am not sure to understand. The documentation on ibrav=2 shows the
> following cell convention:
> 2          cubic F (fcc)
>       v1 = (a/2)(-1,0,1),  v2 = (a/2)(0,1,1), v3 = (a/2)(-1,1,0)
>
> which corresponds to a fcc primitive cell and the position input that
> I provide corresponds to this cell.
> How could the position input be in simple cubic while the cell input
> is a primitive cell ?

I haven't really follow this thread, but from the above I guess the
problem arises from two possible sets of crystal coordinates for fcc,
i.e. one pertaining to cubic conventional cell and the other to
primitive fcc cell. That is, the conventional cell vectors are:

V1=(a,0,0)
V2=(0,b,0)
V3=(0,0,c)

whereas the primitive fcc cell vectors are the one that you stated
above. The "problem" now arises, because the specs of Wyckoff positions
in the input are expressed with respect to conventional V1,V2,V3
vectors, whereas pw.x prints the crystal coordinates with respect to
primitive v1,v2,v3 vectors in the output.

Best regards,
Tone Kokalj
--
J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
(tel: +386-1-477-3523 // fax: +386-1-251-9385)

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