[Wien] P, F or B supercell?

[Stefaan Cottenier]

It tells the code whether the impurity should occupy a cubic (P), bcc 
(B) or fcc (F) sublattice. For instance, if your original unit cell has 
4 atoms and you make a 2x2x2 supercell with 4*2^3=32 atoms, chosing P 
will render a supercell with 32 atoms, one of them being the 'special 
atom' (because you have to break the symmetry in order to have a 
meaningful supercel). Chosing B will give you a supercell with only 16 
atoms, one of them being the special atom (this corresponds to a 2x2x2 
cell with 32 atoms and 2 impurities in a bcc arrangement -- the 
convential bcc cube is twice as large a the primitive bcc cell). Chosing 
F will give you a supercell with only 8 atoms, one of them being the 
special atom (this corresponds to a 2x2x2 cell with 32 atoms and 4 
impurities in a fcc arrangement -- the convential fcc cube is 4 times as 
large a the primitive fcc cell). Not all crystall lattices allow for B 
and/or F.

Stefaan

>Dear all,
>
>I want to calculate the on-site Coulomb interaction parameter U of the Hubbard model using a "supercell" procedure, which was nicely explained in the "Notes" by Madsen and Novak. The example of NiO was easy to follow. 
>Now, trying to repeat the calculations for Cs2CuCl4 (28 non-equiv., 6 equiv. atoms in u. c., orthorhombic, space group: 62 Pnma), I got confused about which type of a supercell to choose for this structure: P, F or B? And why for NiO the F-supercell was the right one? (I tried P, and the scf didn't even converged)
>Could anybody explain the purpose of different types of a supercell?
>Thanks,
>Kateryna Foyevtsova
>
>
>
>
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