[Wien] berryPI

[nilofar hadaeghi]

Dear Sheikh Jamil Ahmed
     I also think that the point of the PhysRevLett.97.267602 is exactly
what you referred. Of course previously in Phys. Rev. B *85*, 104109,
three candidate ground state had been identified but in PhysRevLett.97.267602,
I4/mcm space group has been mentioned as the ground state, and I think Dr.
Gerhard's purpose was making this point clear that calculating the
polarization using I4/mcm space group is meaningless!

On Wed, Sep 9, 2015 at 3:32 PM, nilofar hadaeghi <n.hadaeghi at gmail.com>
wrote:

> 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.
>
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> On Wed, Sep 9, 2015 at 2:52 PM, nilofar hadaeghi <n.hadaeghi at 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 <fecher at 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-bounces at zeus.theochem.tuwien.ac.at [
>>> wien-bounces at zeus.theochem.tuwien.ac.at] im Auftrag von Sheikh Jamil
>>> Ahmed [sahmed5 at 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 <orubel at lakeheadu.ca<mailto:
>>> orubel at 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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