[Wien] Re : Supercell problem of Al2O3

[B. Yanchitsky]

Swati,

Could you provide once more Al and O positions for small cell,
lattice parameters,
and type (size) of supercell you are needed for?

Regards,
Bogdan Yanchitsky

Institute of Magnetism
Vernadsky Blvd., 36-b
03142  Kiev
UKRAINE

Tel. (+380-44) 444 34 20
Fax. (+380-44) 444 10 20



swati chaudhury wrote:
>   Hi Michael and all wien users,
> 
> Thanks for your suggestion.
> I have tried to generate Al2O3 supercell in Wien by following your 
> suggestion. But yet,I have not got proper result.
> The structure files are attached.
> (1)File a.struct : Using Wyckoffpositions (4 Al & 6 O) but without 
> adding transformation : lattice type selected 
> :H                                                            
> Derived space group:193(P 63/mcm)and not the required 167R3cH
> 
> (2) File a2.struct : Wycoff position with added transformation: 
> (2/3,1/3,1/3)+ -Al
> (1/3,2/3,2/3)+ -O
> Lattice type selected : H                              
> Derived space group :1 P1
> 
> (3)File A_latest.struct : Putting all 30 positions with added 
> transformation :
> Lattice selected :P  
> Derived space group : 15 (C 2/c)
> In no process my required space group is derived, ie 167 R-3c:H
> What can I do now? Please help me.
> Swati
> 
> */Michael Fischer <dommiguel at gmx.de>/* wrote:
> 
>     Hello,
> 
>     sorry, I was not aware that you cannot select the space group in
>     hexagonal setting in structgen - as I said, I do not have much
>     experience with rhombohedral and hexagonal cells in WIEN2k.
> 
>     I think you should do as follows: Choose H lattice type and enter the
>     atoms separately. You have to enter 4 aluminium and 6 oxygen positions.
>     The other ones should be generated by the lattice type. In order to
>     find out which positions you need to enter, I suggest you use "WYCKPOS"
>     of www.cryst.ehu.es. There, you enter space group 167 and look at the
>     coordinates given for Wyckoff positions 12c (Al) and 18e (O). For x or
>     z, you substitute the coordinate you have calculated.
>     E.g. for Al at the position (0 0 0.35), i.e. z=0.35, you need to enter
>     the four positions:
>     0 0 0.35
>     0 0 0.15
>     0 0 0.85
>     0 0 0.65
>     Alternatively, select P lattice type and enter all 12 and 18 atoms
>     respectively (more tedious). In addition to the above, you need to
>     apply the transformations for all four Al and six O-positions.
>     (2/3,1/3,1/3) +
>     (1/3,2/3,2/3) +
> 
>     The cause why your second try did not work is easily explained: If you
>     enter only two atoms and do not choose the correct space group,
>     structgen does not know how to generate the symmetry-equivalent atoms.
>     So you end up with a cell that has way too few atoms.
> 
>     Greetings
>     Michael
> 
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> 
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