Re: [Phonopy-users] P1 symmetry but symmetry operations found

[Antonio C. <cam...@fe...>]

Thanks for the answer. It is not still clear to me why there are 
equivalent atoms which can be mapped by symmetry operations if the only 
symmetry operation is the identity. From my understanding, if P1 is the 
space group of the unit cell provided as input, then every atom in the 
unit cell should be unique, then the unit cell is primitive and no 
further reduction is possible.

Antonio

Il 14. 09. 24 15:00, Atsushi Togo ha scritto:
> Hi,
>
> It is not a bug.
>
> P1 corresponds to a space group type.
>
> Space group S is expanded by cosets,
> S = \sum_i (R_i, t_i) T
> where T is the translation group and (R_i, t_i) are the coset 
> representatives (the space group operations). In this way, supercell 
> can not be represented in this way.
>
> The symmetry operations returned in your case are the coset 
> representatives * translations in supercell. However P1 is determined 
> from the primitive cell.
>
> Togo
>
> On Sat, Sep 14, 2024 at 8:29 PM Antonio Cammarata via Phonopy-users 
> <pho...@li...> wrote:
>
>     Dear all
>
>     I am using phonopy 2.28.0 with python 3.9.13 and spglib 2.3.1. I
>     have a
>     unit cell which phonopy recognises to have space group P1, that
>     is, with
>     just the identity as symmetry operation. However, when I call
>     phonopy,
>     for example, to calculate the band structure, it finds space group P1
>     but 3 symmetry operations in the supercell. In fact, if I issue
>     the command
>
>     phonopy --symmetry -c POSCAR_unit_cell
>
>     I get a primitive unit cell PPOSCAR which is smaller than the
>     provided
>     unit cell, and the map of the unique atoms is provided. However,
>     all the
>     symmetry operations associated to the atoms are represented by the
>     identity matrix. Accordingly, I expected that the primitive unit
>     cell is
>     identical to the provided unit cell, as the recognised symmetry is P1
>     and the only symmetry operation is the identity. Please, let me
>     know if
>     I am missing something here.
>
>     Please, here attached you find the unit cell to reproduce the output.
>
>     Thanks a lot in advance for your help!
>
>     All the best
>
>     Antonio
>
>     -- 
>     _______________________________________________
>     doc. Antonio Cammarata, PhD in Physics
>     Associate Professor in Applied Physics
>     Advanced Materials Group
>     Department of Control Engineering - KN:G-204
>     Faculty of Electrical Engineering
>     Czech Technical University in Prague
>     Karlovo Náměstí, 13
>     121 35, Prague 2, Czech Republic
>     Phone: +420 224 35 5713
>     Fax:   +420 224 91 8646
>     ORCID: orcid.org/0000-0002-5691-0682
>     <http://orcid.org/0000-0002-5691-0682>
>     ResercherID: A-4883-2014
>     _______________________________________________
>     Phonopy-users mailing list
>     Pho...@li...
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>
>
>
> -- 
> Atsushi Togo
>
>
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-- 
_______________________________________________
doc. Antonio Cammarata, PhD in Physics
Associate Professor in Applied Physics
Advanced Materials Group
Department of Control Engineering - KN:G-204
Faculty of Electrical Engineering
Czech Technical University in Prague
Karlovo Náměstí, 13
121 35, Prague 2, Czech Republic
Phone: +420 224 35 5713
Fax:   +420 224 91 8646
ORCID: orcid.org/0000-0002-5691-0682
ResercherID: A-4883-2014