[Wien] Problems about super cell and simple cell

[Peter Blaha]

Yes, in principle a supercell must yield the same results as the small
original unit cell.

In order that the WIEN2k symmetry dedection works properly, you should
"label" one of the atoms like   "Ti1"  "C 1" .

Also you should use an "equivalent" k-mesh (or you have converged sets
anyway).

And last but not least, you will NOT be able to simply compare the 
bandstructure pictures. The BZ will be quite different, you have
backfolding,....; so the comparison is of course possible, but not
"straightforward".

Does your DOS look the same ? Is E-tot n-times the original E-tot ? are 
the partial charges the same ?

> Dear wien2k users:
>  I have some questions about the supercell calculation. Just take an 
> example,( I am interested in the bandstructure of solids) TiC is a face 
> centered lattice, I run a scf and get its bandstructure. Then I construct a 
> 2x2x2 supercell (its BZ maybe be 1/8 of a unit cell's), define a P lattice 
> and the labels. After the scf cycle(maybe timecomsuing), I can also get its 
> bandstructure. In common sense, they must be the same. However they are not. 
> How to explain this?
>  Then it's my problem. In my case, the occupancy of some atoms is not 1, so 
> I have to enlarge the unit cell to take an integer number of each atom. 
> After calculation, the bandstructure is quite different from others' 
> calculation. I am wondering the reasons. Can anybody give a suggestion? 
> Thanks in advance!
> 


                                      P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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