<div dir="ltr">Dear Gerhard,<br><br>If I understand correctly, the assumption about the structures of EuTiO3 in <span style="font-size:12.8px">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. </span><br><br><span style="font-size:12.8px">Sheikh</span></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Sep 9, 2015 at 5:24 AM, Fecher, Gerhard <span dir="ltr"><<a href="mailto:fecher@uni-mainz.de" target="_blank">fecher@uni-mainz.de</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">If you check Figure 2 of PhysRevLett.109.267602, you will find that there is NO polarization in I4/mcm !<br>
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 ?<br>
<span class=""><br>
<br>
Ciao<br>
Gerhard<br>
<br>
DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:<br>
"I think the problem, to be quite honest with you,<br>
is that you have never actually known what the question is."<br>
<br>
====================================<br>
Dr. Gerhard H. Fecher<br>
Institut of Inorganic and Analytical Chemistry<br>
Johannes Gutenberg - University<br>
55099 Mainz<br>
and<br>
Max Planck Institute for Chemical Physics of Solids<br>
01187 Dresden<br>
________________________________________<br>
</span>Von: <a href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at">wien-bounces@zeus.theochem.tuwien.ac.at</a> [<a href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at">wien-bounces@zeus.theochem.tuwien.ac.at</a>] im Auftrag von Sheikh Jamil Ahmed [<a href="mailto:sahmed5@lakeheadu.ca">sahmed5@lakeheadu.ca</a>]<br>
Gesendet: Dienstag, 8. September 2015 23:06<br>
<span class="">An: A Mailing list for WIEN2k users<br>
Betreff: Re: [Wien] berryPI<br>
<br>
</span><span class="">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.<br>
<a href="http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.109.267602" rel="noreferrer" target="_blank">http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.109.267602</a><br>
<br>
<a href="http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.97.267602" rel="noreferrer" target="_blank">http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.97.267602</a><br>
<br>
<br>
Hope that helps.<br>
<br>
Sheikh<br>
<br>
--<br>
Sheikh Jamil Ahmed<br>
PhD Student<br>
Department of Material Science and Engineering<br>
McMaster University<br>
1280 Main Street West<br>
Hamilton, Ontario, Canada L8S 4L7<br>
<br>
<br>
</span><span class="">On Tue, Sep 8, 2015 at 3:07 PM, Oleg Rubel <<a href="mailto:orubel@lakeheadu.ca">orubel@lakeheadu.ca</a><mailto:<a href="mailto:orubel@lakeheadu.ca">orubel@lakeheadu.ca</a>>> wrote:<br>
To address your questions...<br>
<br>
> 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?<br>
<br>
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.<br>
<br>
> 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?<br>
<br>
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: <a href="http://arxiv.org/pdf/cond-mat/9903137.pdf" rel="noreferrer" target="_blank">http://arxiv.org/pdf/cond-mat/9903137.pdf</a><br>
I do not see any barriers from BerryPI perspective.<br>
<br>
<br>
Best regards<br>
Oleg<br>
<br>
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