That seems to be the case (http://www.cryst.ehu.es/cgi-bin/cryst/programs/nph-wp-list?gnum=140). If both structures possess the inversion symmetry, it will be pointless to calculate polarization.
Oleg > On Sep 8, 2015, at 03:48, Fecher, Gerhard <fec...@uni-mainz.de> wrote: > > I thought that I4/mcm is also a centrosymmetric space group ? > > Ciao > Gerhard > > DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy: > "I think the problem, to be quite honest with you, > is that you have never actually known what the question is." > > ==================================== > Dr. Gerhard H. Fecher > Institut of Inorganic and Analytical Chemistry > Johannes Gutenberg - University > 55099 Mainz > and > Max Planck Institute for Chemical Physics of Solids > 01187 Dresden > ________________________________________ > Von: wien-boun...@zeus.theochem.tuwien.ac.at > [wien-boun...@zeus.theochem.tuwien.ac.at] im Auftrag von Oleg Rubel > [oru...@lakeheadu.ca] > Gesendet: Dienstag, 8. September 2015 01:03 > An: A Mailing list for WIEN2k users > Betreff: Re: [Wien] berryPI > > The essence of electronic polarization is that it is a “relative” quantity, > i.e., its calculation (and measurement too) requires a reference point. The > reference structure is not always centrosymmetric. An example of > non-centrosymmetric reference structure is zinc-blende GaN that is taken as > P=0 in computing the spontaneous polarization of the wurtzite GaN (see > https://github.com/spichardo/BerryPI/wiki/Tutorial-4:-Polarization-in-GaN). > > For the second part of the question on EuTiO3, enclosed structure files would > certainly help. One possible strategy would be to explore a gradual evolution > of the polarization between cubic and tetragonal structures. > > > I hope this will help > Oleg > > > >> On Sep 7, 2015, at 3:42 AM, nilofar hadaeghi <n.hadae...@gmail.com> wrote: >> >> 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, >> _______________________________________________ >> Wien mailing list >> Wien@zeus.theochem.tuwien.ac.at >> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien >> SEARCH the MAILING-LIST at: >> http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html > > _______________________________________________ > Wien mailing list > Wien@zeus.theochem.tuwien.ac.at > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > SEARCH the MAILING-LIST at: > http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html > _______________________________________________ > Wien mailing list > Wien@zeus.theochem.tuwien.ac.at > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > SEARCH the MAILING-LIST at: > http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html _______________________________________________ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
