[Wien] Space group change during running x sgroup

[Peter Blaha]

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>                                         2.7.0
> 
> Python version 3.8.4
> Spglib version 1.15.1
> 
> Calculator interface: wien2k
> Crystal structure was read from "RbZnBi.struct".
> Unit of length: au
> Displacements creation mode
> Settings:
>    Supercell: [2 2 2]
> Spacegroup: F-43m (216)
> Use -v option to watch primitive cell, unit cell, and supercell structures.
> 
> Number of non-equivalent atoms in RbZnBi.structS-001.in 
> <http://RbZnBi.structS-001.in>: 40
> Number of non-equivalent atoms in RbZnBi.structS-002.in 
> <http://RbZnBi.structS-002.in>: 38
> Number of non-equivalent atoms in RbZnBi.structS-003.in 
> <http://RbZnBi.structS-003.in>: 40
> "phonopy_disp.yaml" and supercells have been created.
> 
> Summary of calculation was written in "phonopy_disp.yaml".
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> 
> 4. It is clear from the output that the space group is not changed. It 
> generates one file for a perfect supercell and 3 files (case-xxx.struct) 
> for supercells with displacements. case-xxx.struct is as follows:


NO !!! It is NOT clear. It only tells you that the starting symmetry was 
216, but the different displaced structures (S-001 ... S-003) have a 
different number of non-equivalent atoms. And it tells you, that S-001 
should have 40 non-equivalent atoms, which is what sgroup gave you.

In fact, it is clear that when you have a high-symmetry structure and 
you displace an atom in a supercell, it MUST reduce symmetry and change 
the space group.

Accept the changes by nn about equivalent atoms. Usually you can then 
neglect the suggestions of sgroup (provided the number of non-equivalent 
atoms did not change and symmetry finds exactly the same number of 
symmetry operations as sgroup), because you do not want to change the 
basis vectors of the cell.




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                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
WWW:   http://www.imc.tuwien.ac.at/TC_Blaha
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