[Wien] berryPI

[Sheikh Jamil Ahmed]

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> 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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