[Wien] AFM type II

[djamel slamnia]

 thanks again sir 
i need to know what is the AFM orders for P3m1 (156) ??? type II or III 

thanks in advance
    Le dimanche 26 janvier 2020 à 20:51:41 UTC+1, Gavin Abo <gsabo at crimson.ua.edu> a écrit :  
 
  
 
   the definition for the compound   a=b = 3.74 A   alpha = beta = 90 gamma = 120   for AFM type I : i creat  superstructure  x super cell target lattice H  :  x =1,   y = 1 ,  Z =2  then x sgroup, program define automatically the space group the same of my original space group 156 without warrning 
   
 
As you have described above (for Z=2), your attempt at creating a supercell has failed as "x sgroup" collapsed the supercell structure back to the non-supercell structure.
 
As mentioned on the FAQ page for supercell construction, you need to displace an atom, change an atom, or use a special label:
 
 
http://susi.theochem.tuwien.ac.at/reg_user/faq/supercells.html
 
In order to keep the supercell without "x sgroup" reducing it back to the original structure, refer to previous posts in the mailing list archive about breaking the symmetry.  A few of the many posts about that as examples are at the three links below:
 
 https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg18380.html
 https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg01866.html
 https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg15517.html 

 
 
  but when try to do it for type II : x super cell  P :  x =1,   y = 1 ,  Z =1 x sgroup could not define the space group 
   
 
In section "3.12 Setting up a new case" on page 29 in the WIEN2k 19.1 usersguide [ http://susi.theochem.tuwien.ac.at/reg_user/textbooks/usersguide.pdf ], there is the statement:
 
 "Alternatively with the new StructGen you can specify the spacegroup and only the inequivalent positions. The equivalent ones will be generated automatically."
 
 
This means spacegroups in WIEN2k are defined according to the inequivalent positions and not by the equivalent positions. 
 
 
For the case above (Z=1), it is likely that "x supercell" found some equivalent positions in the original structure and automatically added special labels to them changing them into inequivalent positions. Thus, a supercell structure was successfully created.  If you want the supercell structure to reduce back to the original structure, you would likely just need to remove all or some of the special labels in StructGen before running "x sgroup".
 
 
For understanding the inequivalent and equivalent positions with WIEN2k spacegroups, the example in the post at the following link might helpful:
 
http://zeus.theochem.tuwien.ac.at/pipermail/wien/2013-January/018171.html

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