[Wien] W2WEB problem with sructure in spgrp 166

[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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