[Wien] Re : Supercell problem of Al2O3

[B. Yanchitsky]

swati chaudhury wrote:
> (i) For the hexagonal axes if I add 30 indivisual atoms (12-Al,18-O) the 
> space group is o.k.But in supercell ( 2  2   1  ,120 atoms) dstart is 
> not ending (symmetry 1).
> (ii)Similarly if I put 12 positions against one Al and 18 positions 
> against one O, again space group is o.k but dstart gives ROTDEF error in 
> unit cell (12 symmetry generated, expected is 36).
> What can I do next?

In general, once you have a created unit cell, you create a super cell with supercell,
but the super cell file is raw, you have to introduce some symmetry break, for example,
provide extra vacuum space, distort atoms from their positions, remove an atom to model
a hole, add an impurity atom, etc....
Next, you have to set up the modified cell according to its symmetry. Try sgroup for that.
If you still have problems on that, send me your structure files.

120 atoms cell is a big case, estimated matrix size would be near 12000x12000,
with a lower symmetry, it might be difficult for calculations.

 > unit cell (12 symmetry generated, expected is 36).

That's ok for 12 operations, for wien package 36 is wrong.

Regards,

Bogdan Yanchistky

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