[Wien] Re : Supercell problem of Al2O3

[swati chaudhury]

  Hi,        
Thaks for the help. my problem is to generate Al2O3 supercell with vacuum slab in Wien2k.Basic inputs are given below for rhombohedral settings:

Cell parameters: 4.7626   4.7626   13.0032(ang) ;  90.000  90.00  90.00
Space group: 167 R-3c
Positions:
Al:0.3519208     0.3519208     0.3519208
   0.8519208     0.8519208     0.8519208
   0.1480792     0.1480792     0.1480792
   0.6480792     0.6480792     0.6480792
O: 0.9437520     0.5562480     0.2500000
   0.5562480     0.2500000     0.9437520
   0.2500000     0.9437520     0.5562480
   0.0562480     0.4437520     0.7500000
   0.4437520     0.7500000     0.0562480
   0.7500000     0.0562480     0.4437520

Thanks in advance.

Swati

   
   
  "B. Yanchitsky" <yan at im.imag.kiev.ua> wrote:
  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 /* 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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