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Hi Mostaffa</div>
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To close the loop here, I appreciate your response, though I am familiar with the Modern Theory and agree that the dipole from any particular cell is not useful in isolation. However, the calculated dipole numbers should not jump from e.g. -10 to +5 in the
last iteration as the SCF converges!</div>
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Nonetheless, it turns out the problem is something wrong with the centrally-provided build on the machine I'm using. When I compile pw.x myself (ver. 6.7, but meh) on the same or another machine, the dipoles converge as I expect them to.</div>
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Thanks for your help.</div>
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Ciao</div>
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Terry</div>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>From:</b> users <users-bounces@lists.quantum-espresso.org> on behalf of Mostafa Youssef via users <users@lists.quantum-espresso.org><br>
<b>Sent:</b> Tuesday, 19 January 2021 7:44 PM<br>
<b>To:</b> users@lists.quantum-espresso.org <users@lists.quantum-espresso.org><br>
<b>Subject:</b> Re: [QE-users] Finite electric field polarisation</font>
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<div class="x_gmail_default" style="font-family:verdana,sans-serif">Dear Terry,</div>
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<div class="x_gmail_default" style="font-family:verdana,sans-serif">The dipole results need post-processing. One needs to subtract n x polarization quantum to obtain a meaningful polarization. n is an integer.
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<div class="x_gmail_default" style="font-family:verdana,sans-serif">Consider a simple dielectric like MgO at zero field. pw.x may give you different dipoles in all directions, although physically in all directions the net dipoles are zero. If you post-process
as I indicated above you get zero dipole as it should.</div>
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<div class="x_gmail_default" style="font-family:verdana,sans-serif">A good starter on this topic is this paper:</div>
<div class="x_gmail_default" style="font-family:verdana,sans-serif"><a href="https://www.sciencedirect.com/science/article/abs/pii/S0022459612003234">https://www.sciencedirect.com/science/article/abs/pii/S0022459612003234</a></div>
<div class="x_gmail_default" style="font-family:verdana,sans-serif">A free arXiv version of it is also available.<br>
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<div class="x_gmail_default" style="font-family:verdana,sans-serif">Mostafa <br>
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<div class="x_gmail_default" style="font-family:verdana,sans-serif">AUC</div>
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