[Pw_forum] A query about the PRIMCOORD parameter of the Xcrysden.

[Stefano de Gironcoli]

the two choices are equivalent (not identical).
You may want to try to visualize the two and see the difference.

Stefano de Gironcoli - SISSA and DEMOCRITOS

> Here is an example of ZnS crystal structure: 
>
>  CRYSTAL                                        see (1)
>  PRIMVEC
>     0.0000000    2.7100000    2.7100000         see (2)
>     2.7100000    0.0000000    2.7100000
>     2.7100000    2.7100000    0.0000000
>  CONVVEC
>     5.4200000    0.0000000    0.0000000         see (3)
>     0.0000000    5.4200000    0.0000000
>     0.0000000    0.0000000    5.4200000
>  PRIMCOORD
>  2 1                                            see (4)
>  16      0.0000000     0.0000000     0.0000000  see (5)
>  30      1.3550000    -1.3550000    -1.3550000
> ---------------------------------------------
>
> In the above descriptions,  if we take the sulfur atom position as the origin, than the Zinc atom should have the coordinates  (-1.3550000    -1.3550000    -1.3550000).  I don't konw why it should be  (1.3550000    -1.3550000    -1.3550000) in the Xcrysden's documents.
>
> Who can give me some hints on this?
>