[Wien] precision problem

[Jorissen Kevin]

Hi Torsten,
what you say is correct, only I would not call it an error.
Equivalency is determined by two things :
* equivalent atoms must have identical chemical environment
* there must be a symmetry operation of the lattice connecting equivalent atoms.
 
Nn checks the first condition, and sgroup takes care of the second one.  Obviously the second condition will sometimes reduce the equivalency obtained by the first condition only.
So after running nn, one must always run sgroup also.  Even if one chooses to ignore the lattice changes proposed by sgroup (CXZ!), one *must* check that the equivalency is not changed by symmetry.
 
Kevin.
 

	-----Oorspronkelijk bericht----- 
	Van: Torsten Andersen [mailto:thor at physik.uni-kl.de] 
	Verzonden: wo 11/5/2003 10:02 
	Aan: wien at zeus.theochem.tuwien.ac.at 
	CC: 
	Onderwerp: Re: [Wien] precision problem
	
	

	Dear stargmoon,
	
	I am not sure what your problem is, but I would say that if symmetry and
	  sgroup does not complain and sgroup does not reduce the unit cell, it
	is safe to ignore this error. I have sometimes gotten it when I
	calculate thin films, and nn wants two atoms to be equal although they
	by symmetry are not.
	
	Best regards,
	Torsten Andersen.
	
	stargmoon wrote:
	> Dear wien2k user,
	> 
	> I met a problem in doing 'x nn'. My input structure is the structure
	> with space group P-3m1, and one type of atoms occupy the "6i"
	> positions.I think I can be sure that my input structure is correct,
	> because the space group analysis with wien2k and other software all
	> indicate the right space group. However, after the 'x nn' finished, I
	> always got the error information, that is, the Mult not equal and ityp
	> not equal. I checked the number and the distance of the nearest
	> neighbors printed out in the file case.outputnn, but I can't find out
	> any difference between those atoms which was declared to be not equal by
	> 'x nn'. Have you ever met the same problem, and can I ignore those error
	> (because the space group is the same as expected)?
	> 
	> Thanks for your reply!
	> 
	> Best,
	> 
	> stargmoon
	>
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	--
	Dr. Torsten Andersen                     TA-web: http://deep.at/myspace/
	AG Hübner, Department of Physics, Kaiserslautern University, and
	Condensed Matter Theory Group, Department of Physics, Uppsala University
	Web: http://www.fysik4.fysik.uu.se/         http://www.physik.uni-kl.de/
	
	
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