[Wien] berryPI

[Sheikh Jamil Ahmed]

Dear Gerhard,

If I understand correctly, the assumption about the structures of
EuTiO3 in PhysRevLett.97.267602
is not accurate enough. The only consider the ground state to be Pm3_m and
then do a compression study with P4/mm. PhysRevLett.109.267602 on the other
hand pointed that the structure of bulk EuTiO3  in ground state should
be I4/mcm. Then, under compression the transition goes from I4/mcm to I4cm
to P4mm.

Sheikh

On Wed, Sep 9, 2015 at 5:24 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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