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Dear Abhirup;</div>
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I have faced the same problem, but for a magnetic insulator; However the nature of the problem is similar. </div>
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Please see example 02 in QE for hp.x :</div>
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"When you use linear response theory to determine U, in DFPT there is a metallic correction at q=0 that is proportional to the inverse of DOS at the Fermi level. (Rev. Mod. Phys. 73, 515 (2001)) and if the Fermi level is too small, the Fermi energy shift in
DFPT will be very large."</div>
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I would say you can try to find the U parameter using rotationally invariant scheme instead. </div>
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<font face="Times New Roman, Times, serif" size="3">Best regards; </font></p>
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<span style="font-family:"Times New Roman",Times,serif">Mona Asadi Namin</span></p>
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<span style="font-family:"Times New Roman",Times,serif">Center for simulational physics</span></p>
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<span style="font-family:"Times New Roman",Times,serif">University of Georgia</span></p>
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<span style="color:rgb(0,0,0); font-family:"Times New Roman",Times,serif">E</span><span style="font-family:"Times New Roman",Times,serif">mail:</span><span style="font-family:"Times New Roman",Times,serif; color:rgb(149,79,114)"><a href="mailto:mona.a@uga.edu" style="font-family:"Times New Roman",serif; color:rgb(149,79,114)">mona.a@uga.ed</a>u<a href="mailto:mona.a@uga.edu"></a></span><span style="font-family:"Times New Roman",Times,serif"> </span></p>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> users <users-bounces@lists.quantum-espresso.org> on behalf of Abhirup Patra <abhirupp@sas.upenn.edu><br>
<b>Sent:</b> Saturday, July 25, 2020 12:20 AM<br>
<b>To:</b> Quantum ESPRESSO users Forum <users@lists.quantum-espresso.org><br>
<b>Subject:</b> [QE-users] Problem with hp.x for f-metals</font>
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<div><font color="BA0C2F">[EXTERNAL SENDER - PROCEED CAUTIOUSLY]</font><br>
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<div class="x_gmail_default" style="font-size:large">Hello, <br>
</div>
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<div class="x_gmail_default" style="font-size:large">I am trying to compute Hubbard U using hp.x for Cerium, however, it seems that after few iterations the code stopped with the following message:</div>
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<div class="x_gmail_default" style="font-size:large"> atom # 1 q point # 1 iter # 395<br>
Fermi energy shift (Ry) = -0.5530E+01 -0.2375E-07<br>
<br>
WARNING: The Fermi energy shift is too big!<br>
This may happen in two cases:<br>
1. The DOS at the Fermi level is too small:<br>
DOS(E_Fermi) = 0.1303E+04<br>
This means that most likely the system has a gap,<br>
and hence it should NOT be treated as a metal<br>
(otherwise numerical instabilities will appear).<br>
2. Numerical instabilities due to too low cutoff<br>
for hard pseudopotentials.<br>
<br>
Stopping...</div>
<div class="x_gmail_default" style="font-size:large"><br>
</div>
<div class="x_gmail_default" style="font-size:large">Any help would be appreciated.
<br>
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<div class="x_gmail_default" style="font-size:large">Best,</div>
<div class="x_gmail_default" style="font-size:large">Abhirup<br>
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