<div dir="ltr"><div>Dear <span name="Sheikh Jamil Ahmed">Sheikh Jamil Ahmed</span></div><div><span name="Sheikh Jamil Ahmed"> I also think that the point of the <span style="font-size:12.8px">PhysRevLett.97.267602 is exactly what you referred. Of course previously in Phys. Rev. B <b>85</b>, 104109, three candidate ground state had been identified but in <span style="font-size:12.8px">PhysRevLett.97.267602, I4/mcm space group has been mentioned as the ground state, and I think</span> Dr. Gerhard's purpose was making this point clear that calculating the polarization using I4/mcm space group is meaningless! </span></span></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Sep 9, 2015 at 3:32 PM, nilofar hadaeghi <span dir="ltr"><<a href="mailto:n.hadaeghi@gmail.com" target="_blank">n.hadaeghi@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>Dear <span name="Fecher, Gerhard">Fecher, Gerhard</span></div><div><span name="Fecher, Gerhard"> your recommended papers have been carefully studied. </span></div><div><span name="Fecher, Gerhard">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. </span></div><div>Thank you for your attention. </div><div> </div><span name="Fecher, Gerhard"><font face="AdvP6F00" size="3"><font face="AdvP6F00" size="3"></font><div> </div><p><div> </div><p></p><div> </div><p></p></p></font><div> </div><p> </p><p> </p><div> </div></span><div> </div><div><p><span name="Fecher, Gerhard">.</span></p></div></div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Sep 9, 2015 at 2:52 PM, nilofar hadaeghi <span dir="ltr"><<a href="mailto:n.hadaeghi@gmail.com" target="_blank">n.hadaeghi@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;padding-left:1ex;border-left-color:rgb(204,204,204);border-left-width:1px;border-left-style:solid"><div dir="ltr"><div>Dear Pleg Rubel and <span name="Sheikh Jamil Ahmed">Sheikh Jamil Ahmed</span></div><div><span name="Sheikh Jamil Ahmed"> I really appreciate your attention and guidance. I was really confused and you helped me a lot.</span></div><div><span name="Sheikh Jamil Ahmed">Best regards,</span></div><div><span name="Sheikh Jamil Ahmed">N.Hadaeghi </span></div><div><span name="Sheikh Jamil Ahmed"> </span></div></div><div><div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Sep 9, 2015 at 2:24 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:0px 0px 0px 0.8ex;padding-left:1ex;border-left-color:rgb(204,204,204);border-left-width:1px;border-left-style:solid">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><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" target="_blank">wien-bounces@zeus.theochem.tuwien.ac.at</a> [<a href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at" target="_blank">wien-bounces@zeus.theochem.tuwien.ac.at</a>] im Auftrag von Sheikh Jamil Ahmed [<a href="mailto:sahmed5@lakeheadu.ca" target="_blank">sahmed5@lakeheadu.ca</a>]<br>
Gesendet: Dienstag, 8. September 2015 23:06<br>
<span>An: A Mailing list for WIEN2k users<br>
Betreff: Re: [Wien] berryPI<br>
<br>
</span><span>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" target="_blank" rel="noreferrer">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" target="_blank" rel="noreferrer">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>On Tue, Sep 8, 2015 at 3:07 PM, Oleg Rubel <<a href="mailto:orubel@lakeheadu.ca" target="_blank">orubel@lakeheadu.ca</a><mailto:<a href="mailto:orubel@lakeheadu.ca" target="_blank">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" target="_blank" rel="noreferrer">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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