[Wien] Re : Supercell problem of Al2O3

[swati chaudhury]

Hi Yanchistky and all Wien users,
  Thanks for your suggestion and sorry for late response. Actually in the mean time I have done my homework.
  I have generated ( 2 2 1 ) supercell with vacuum slab 4 bohr .At last, scf of the supercell is converged nicely by reducing Rkmax to 5.00.Space group of the supercell is !67 R-3c.
  But one more query,is the (2 2 1 )type supercell treatment (for Al2O3) correct or not ?
  The above same calculation with Rkmax 6.00,dstart is completed without any problem.But scf is ended after lapw0 in 1st cycle with an error message given below:
  forrtl:severe (174) : SIGSEGV,segmentation fault occured.
  Stack trace terminated abnormally.
  Added information: ( 2 2 2 ) supercell calculation is terminated in dstart step becoz of insufficient virtual memory problem. Total number of atoms in this supercell is 240.
  Please suggest me.
  Regards.
  Swati



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

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

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


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