[Pw_forum] Doubt in ibrav = 7

[Tone Kokalj]

On Sat, 2014-09-13 at 22:39 +0100, Youssef Aharbil wrote:
> Dear QE Users,
> 
> 
> I have encountered lot of problems with ibrav = 7, when plotting the
> structure with xcrysden it seems that the atoms aren't at the right
> positions, using "crystal" for ATOMIC_POSITIONS give incorrect atoms
> coordinates while visualization, 

Such problems typically stem from lattice definition mismatches, e.g,
the user and pw.x use two different cell-definitions.
E.g., see this thread:
http://qe-forge.org/pipermail/pw_forum/2014-May/thread.html#104278 

> I corrected that issue using "bohr" in stead off "crystal"  (of course
> by doing conversion), but it seems that one atom is missing (Second La
> atom with coordinate 0.5 0 0.25 ) even if it exist well in the input
> file.
> 
> Please tell me if that's just a bug on xcrysden or something is wrong with my data.
> 

Your structure looks OK and there is no missing atom, although it may
appear otherwise. The reason is that due to some round-off error two
periodic replicas of the La atom are not drawn (but notice that they are
periodic replicas); sometimes this happens and it is inconvenient. If
you drawn more units cells (say, 2x2x1) you will notice that noting is
missing (i.e. these replicas will appear).


Best regards,
-- 
Anton Kokalj
J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia 
(tel: +386-1-477-3523 // fax:+386-1-477-3822)

Please, if possible, avoid sending me Word or PowerPoint attachments.
See:  http://www.gnu.org/philosophy/no-word-attachments.html