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<div style="margin-top:0; margin-bottom:0">To whom it may concern:<br>
<br>
While running Berry Phase analysis on BaTiO3 via pw.x (version 7.0) I found a mismatch in the output value.<br>
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<div style="margin-top:0; margin-bottom:0">I figure out that the value of weighted average of the Electronic Phase printed in the output file get shift by a factor of +1.<br>
</div>
<div style="margin-top:0; margin-bottom:0"><br>
In the following temporary link, you can find the files of two calculations on this system: one with reasonable results and another with unexpected results.
<br>
<a href="https://www.transfernow.net/dl/20220513pe4LRGy" target="_blank" rel="noopener noreferrer" id="LPlnk534915" previewremoved="true"><span id="LPlnk534915">https://www.transfernow.net/dl/20220513pe4LRGy</span></a><span id="LPlnk534915">
</span><br>
<br>
<i><u>Our Idea:</u></i></div>
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<div style="margin-top:0; margin-bottom:0">This process seems to happen, whenever the averaged Electronic Phase lies outside the range of [-0.5, +0.5], leading to an unexpected Total phase and resulted Polarization value.<br>
</div>
<div style="margin-top:0; margin-bottom:0">Although polarization is a multiple value given by:<b> Ps +/- n*mod,</b> the above mentioned shift cannot correctly compensated by the
<b>mod</b>, such to get a reasonable value for this system. <br>
</div>
<div style="margin-top:0; margin-bottom:0"><br>
Looking at the source code: <b>bp_c_phase</b>.<b>f90</b> around the lines=<b>764-806</b><b>,
</b><br>
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<div style="margin-top:0; margin-bottom:0">The variables <b>pdl_elec_up</b>,<b> pdl_elec_dw</b> and
<b>pdl_elec_tot </b>seems to be renormalized as follow:</div>
<div style="margin-top:0; margin-bottom:0"><br>
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<div style="margin-top:0; margin-bottom:0"><b>805: ! you need to do mod again!</b><b><br>
</b></div>
<div style="margin-top:0; margin-bottom:0"><b>806:</b> <b>pdl_elec_tot=pdl_elec_tot-nint(pdl_elec_tot)
</b> <br>
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<div style="margin-top:0; margin-bottom:0"><br>
</div>
<div style="margin-top:0; margin-bottom:0">Where <b>nint = </b><b>+/- 1 </b> and not the
<b>mod value</b>.<br>
</div>
<div style="margin-top:0; margin-bottom:0"><b><br>
</b></div>
<div style="margin-top:0; margin-bottom:0">although in the previous lines, the value seems already to be fixed in the range of -Pi to +Pi</div>
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</div>
<div style="margin-top:0; margin-bottom:0"><b>771: !REC Third you need to fix jumps before you take average</b><br>
<b>762: if(abs(t+1d0-t1).lt.abs(t-t1))phik(istring)=phik(istring)+tpi.</b><b><br>
</b><br>
<i><u>Our Question:</u></i></div>
<div style="margin-top:0; margin-bottom:0">1) why there's this renormalization at line 806?<br>
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<div style="margin-top:0; margin-bottom:0">2) why there's a change of +/- 1 instead of +/-2?<br>
<br>
Thank you for your consideration<br>
Regards</div>
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</div>
<div style="margin-top:0; margin-bottom:0">Samuele Spreafico<br>
</div>
<div style="margin-top:0; margin-bottom:0">Department of Chemistry and Pharmacy<br>
Professor for Computational Chemistry (ICMM)</div>
CCC, Nägelsbachstraße 25<br>
91052 Erlangen</font><span id="ms-rterangepaste-end"></span><br>
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