[Pw_forum] symmetry operations

[degironc]

Are you using CRYSTAL coordinates?
in this case 3/4 1/4 3/4 and 1/4 1/4 1/4 are NOT equivalent.
the former is wrong and corrseponds to the following cartesian coordinates
(from the PWscf output)
         2           Si  tau(  2) = (  -0.7500000   0.5000000   0.5000000  )
which are obviously wrong.
stefano


Miguel A. Salvadó wrote:

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> Dear PWusers:
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> I do not understand how PWSCF generate the symmetry operations from 
> ibrav and crystal coordinates.
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> A simple example: C diamond (Fd-3m) with C at 8a (0,0,0) (Cell choice 1).
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> If I run a calculation with ibrav 2 (cubic F-centered) and two C atoms 
> at 0,0,0 and 3/4,1/4,3/4 the program found 16 symmetry operations.
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> But if I change the second position to the equivalent one 1/4 1/4 1/4, 
> then the program found successfully 48 symmetry operations.
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> I have found this problem with more complex structures and it is not 
> easy to check all the possibilities of equivalent positions combinations.
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> Any kind of help will be welcome,
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> Best wishes,
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> Miguel A. Salvadó
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> Miguel A. Salvadó
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> Dpto. Quimica Fisica y Analitica
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> Universidad de Oviedo
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> Spain
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> E-mail: mass at uniovi.es
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