[Wien] W2WEB problem with sructure in spgrp 166

[Peter Blaha]

Sorry Gerhard,
I cannot reproduce that.
structgen of w2web does not change the positions in my version.

Regards
Peter

Am 10.06.2025 um 11:17 schrieb Fecher, Gerhard:
> Dear Peter,
> I found a problem in W2WEB StructGen with hexagonal structures (166_R-3m)
> 
> The structure was read in with P1 from a cif file and the symmetry was set by sgroup,
> the resulting structure file was:
>      Structure from sgroup ==> Cu2MnAl_hex.struct_before
> 
> This structure runs without any problems and is correct when viewing it with XCrysden.
> (as it is a subgroup of 225, the results are the same besides some numerical uncertainties)
> 
> To change c/a the structure I wanted to use StructGen in W2Web
> However, struct.pl from ...../Wien2k/Wien2k/SRC_w2web/libs changed the positions of the atoms
> to be the same (0,0,0) such that it could not longer be used.
> 
> This appears already without any changes of the structure after Save Structure
> as is seen in:
>      Structure after StructGen: edit STRUCT file / Save Structure ==> Cu2MnAl_hex.struct_after
> 
> I do not see why it changes the Wyckoff positions from 1b or 2c to 1a (0,0,0 independent on axis choice)
> Even more confusing: if the POS 1 is 0, 0, 0, then there should not be a position POS 2
> in rhombohedral coordinates only Wyckoff position c has a twofold multipicity
> (Indeed in hexagonal coordinates one has for a,b,c a 3 fold multiplicity)
> 
> It seems that struct.pl is doing something wrong. Bug or feature ?
> 
> For the future it might be more comfortable to distinguish the two set-ups of spgr 166 and the respective Wyckoff positions.
> (01 Hexagonal, 02 Rhombohedral Axes according to the International Tables Volume A)
> and also similar ones
> 
> Ciao
> Gerhard
> 
> DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
> "I think the problem, to be quite honest with you,
> is that you have never actually known what the question is."
> 
> ====================================
> Dr. Gerhard H. Fecher
> Institut of Physics
> Johannes Gutenberg - University
> 55099 Mainz
> 
> 
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Peter Blaha,  Inst. f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-158801165300
Email: peter.blaha at tuwien.ac.at
WWW:   http://www.imc.tuwien.ac.at      WIEN2k: http://www.wien2k.at
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