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

[Atsushi T. <atz...@gm...>]

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
> ResercherID: A-4883-2014
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-- 
Atsushi Togo