[Wien] berryPI

[nilofar hadaeghi]

Dear all
     I have studied some papers whose authors are S.J.Ahmed or O.Rubel  in
which building the centrosymmetric and noncentrosymmetric structure for the
calculation of spontaneous polarization has been explained, but it is still
ambiguous for me.
Could you please help me whether the noncentrosymmetric structure must
exist in the nature or it is enough to apply a displacement to the central
atom of the centrosymmetric structure and then use the new structure as the
noncentrosymmetric one?!
For instance I am working on EuTiO3 in which a structural transition at
temperature 282(k) from cubic to tetragonal ( from Pm3m space group to
I4/mcm) occurs. Now, would you please help me whether I use the structure
in I4/mcm space group as the noncentrosymmetric structure or I must change
the positions of the centrosymmetric structure and use the
achieved structure as the noncentrosymmetric one?
I am using WIEN2k 14.2, Python version: 2.7.3 and Numpy version: 1.6.2.
Sincerely yours,
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