Dear Fecher, Gerhard
     your recommended papers have been carefully studied.
I understood that in this compound, different structural phases whether for
the unstrained or strained states can be occurred among which just the ones
whose space groups are not centrosymmetric would be meaningful to be used
in calculating the polarization. For instance in the strained state, it has
been allowed to calculate the polarization for the space group P4mm. and
not I4/mcm The relation between the  oxygen octahedra tilting and the low
energy symmetry is still unknown.
Thank you for your attention.














.

On Wed, Sep 9, 2015 at 2:52 PM, nilofar hadaeghi <n.hadae...@gmail.com>
wrote:

> Dear Pleg Rubel and Sheikh Jamil Ahmed
>      I really appreciate your attention and guidance. I was really
> confused and you helped me a lot.
> Best regards,
> N.Hadaeghi
>
>
> On Wed, Sep 9, 2015 at 2:24 AM, Fecher, Gerhard <fec...@uni-mainz.de>
> wrote:
>
>> If you check Figure 2 of PhysRevLett.109.267602, you will find that there
>> is NO polarization in I4/mcm !
>> and in the  PhysRevLett.97.267602 you find "... the crystallographic
>> symmetry  becomes P4/mm", now compare this to the Fig.2 of the first
>> reference, what do you see ?
>>
>>
>> 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 Sheikh Jamil
>> Ahmed [sahm...@lakeheadu.ca]
>> Gesendet: Dienstag, 8. September 2015 23:06
>> An: A Mailing list for WIEN2k users
>> Betreff: Re: [Wien] berryPI
>>
>> I would like to add that EuTiO3 seems to be a multiferroic compound with
>> ground state being antiferromagnetic- paraelectric system (I4/mcm). Then,
>> under some compressive or tensile epitaxial strain, several types of
>> transition is possible (For example, antiferromagnetic- ferroelectric or
>> ferromagnetic- ferroelectric) depending on the magnitude and type of
>> strain. The following articles address this issue very well.
>> http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.109.267602
>>
>> http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.97.267602
>>
>>
>> Hope that helps.
>>
>> Sheikh
>>
>> --
>> Sheikh Jamil Ahmed
>> PhD Student
>> Department of Material Science and Engineering
>> McMaster University
>> 1280 Main Street West
>> Hamilton, Ontario, Canada L8S 4L7
>>
>>
>> On Tue, Sep 8, 2015 at 3:07 PM, Oleg Rubel <oru...@lakeheadu.ca<mailto:
>> oru...@lakeheadu.ca>> wrote:
>> To address your questions...
>>
>> > I4/mcm is centrosymmetric. I studied the tutorial related to GaN and it
>> helped me very much. So I conclude to calculate the difference in
>> polarization, two structures that at least one of them should not be
>> centrosymmetric are needed, Is it correct?
>>
>> That’s correct. When the structure file contains the inversion symmetry,
>> Wien2k switches from complex to real version for wave functions. Then there
>> is no phase information to be processed.
>>
>> > Would you please guide me whether it is allowed to calculate the
>> difference in polarization between a strained and unstrained state of a
>> system by implementing the berryPI on each of them separately and then
>> subtract them ?! if it going to, what does the derived polarization
>> describe?! Piezoelectricity(since it is the difference in polarization
>> caused by strain) or spontaneous polarization?
>>
>> You are heading towards piezoelectric coefficients. There are some
>> technicalities, such as clamped vs relaxed ion approximation, proper vs
>> improper. Here is a good reference:
>> http://arxiv.org/pdf/cond-mat/9903137.pdf
>> I do not see any barriers from BerryPI perspective.
>>
>>
>> Best regards
>> Oleg
>>
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>
>
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