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<pre style="margin-top:0;margin-bottom:0;white-space:pre-wrap;"><font style="font-family: courier, courier new, monospace, serif, "EmojiFont";" size="2" face="courier,courier new,monospace" color="black"><span style="font-size:14px;"><span style="font-size: 11pt; font-family: Arial, Helvetica, sans-serif; color: rgb(0, 0, 0);">Dear </span><span style="font-size: 11pt; font-family: Arial, Helvetica, sans-serif; color: rgb(0, 0, 0);">Poonam Sharma,</span></span></font></pre>
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<p>Regarding the convergence with respect to the k points mesh: I would suggest to have a look at the Quantum ESPRESSO input generator
<a href="https://www.materialscloud.org/work/tools/qeinputgenerator" class="OWAAutoLink" id="LPlnk423563" previewremoved="true">
https://www.materialscloud.org/work/tools/qeinputgenerator</a></p>
<p>You just upload your structure and choose between "normal", "fine", and "very fine" k points mesh. Even if the lattice parameters a, b, and c are all different, this tool will automatically find out which k points mesh to use. Then you can vary these k points
meshes a bit and see how the results change, and eventually see when your results converge with a desired accuracy/precision.</p>
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<p>HTH</p>
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<p>Iurii<br>
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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 poonamsharma <poonamkaushik40@gmail.com><br>
<b>Sent:</b> Thursday, November 11, 2021 8:38:58 AM<br>
<b>To:</b> Quantum ESPRESSO users Forum<br>
<b>Subject:</b> Re: [QE-users] Different band gap in unitcell and in supercell</font>
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<pre style="font-family:courier,"courier new",monospace;font-size:14px;white-space:pre-wrap;margin-top:0px;margin-bottom:0px;color:rgb(0,0,0)">Dear Sir,</pre>
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<pre style="font-family:courier,"courier new",monospace;font-size:14px;white-space:pre-wrap;margin-top:0px;margin-bottom:0px;color:rgb(0,0,0)">>The band gap should not change: in a supercell you will have more electronic
>bands but the band gap must remain the same. Again, please check that you do
>all properly or share your files.
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<pre style="font-family:courier,"courier new",monospace;font-size:14px;white-space:pre-wrap;margin-top:0px;margin-bottom:0px;color:rgb(0,0,0)">Thank you so much fr this suggestion.</pre>
<pre style="font-family:courier,"courier new",monospace;font-size:14px;white-space:pre-wrap;margin-top:0px;margin-bottom:0px;color:rgb(0,0,0)"> I guess I am taking wrong K points. Also I didn't perform the K points convergence test for supercell. This may be one the reson of this discrepancy. I'll chk this again, also I am thinking to perform convergence test for each supercell.</pre>
<pre style="font-family:courier,"courier new",monospace;font-size:14px;white-space:pre-wrap;margin-top:0px;margin-bottom:0px;color:rgb(0,0,0)">Only one query I have, my a,b,c parameters for unitcell are 13.764, 3.699, 3.95. It is bulk system. For K points convergence wrt energy, I took K points sets like 2x2x2 3x3x3... like this , and at 5x5x5 I obtained a good convergence. Since my a,b,c are not equal so I am taking in SCF calculation 5X10X9.</pre>
<pre style="font-family:courier,"courier new",monospace;font-size:14px;white-space:pre-wrap;margin-top:0px;margin-bottom:0px;color:rgb(0,0,0)">This 5X10X9 set is correct to to take although at 5X5X5 I obtained the convergence.</pre>
<pre style="font-family:courier,"courier new",monospace;font-size:14px;white-space:pre-wrap;margin-top:0px;margin-bottom:0px;color:rgb(0,0,0)">Thank you so much once again.</pre>
<pre style="font-family:courier,"courier new",monospace;font-size:14px;white-space:pre-wrap;margin-top:0px;margin-bottom:0px;color:rgb(0,0,0)"><br></pre>
<pre style="font-family:courier,"courier new",monospace;font-size:14px;white-space:pre-wrap;margin-top:0px;margin-bottom:0px;color:rgb(0,0,0)">Thanks and regards,</pre>
<pre style="font-family:courier,"courier new",monospace;font-size:14px;white-space:pre-wrap;margin-top:0px;margin-bottom:0px;color:rgb(0,0,0)">Poonam Sharma </pre>
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<div dir="ltr">Poonam Sharma
<div>Research Scholar </div>
<div>Department of Physics</div>
<div>Indian Institute of <span>Technology Bombay</span></div>
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<div dir="ltr" class="gmail_attr">On Sun, Nov 7, 2021 at 9:17 AM poonamsharma <<a href="mailto:poonamkaushik40@gmail.com">poonamkaushik40@gmail.com</a>> wrote:<br>
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<div dir="ltr"><span style="color:rgb(35,38,41);font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","Liberation Sans",sans-serif;font-size:15px">Dear users,</span></div>
<div dir="ltr"><span style="color:rgb(35,38,41);font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","Liberation Sans",sans-serif;font-size:15px">I am trying to calculate the bandgap for one system in the unit cell and in the supercell of 2x2x1 and 3x1x1.
Although 3x1x1 gives the same bandgap as I got from the unit cell (1.80 eV) but 2x2x1 is giving 1.75 eV. I kept the input files settings same in supercells as in-unit cell including K- POINTS. I observed this bandgap by plotting the dos. I think the bandgap
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<div><span style="color:rgb(35,38,41);font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","Liberation Sans",sans-serif;font-size:15px">Is this 1.75 eV is acceptable.</span></div>
<div><span style="color:rgb(35,38,41);font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","Liberation Sans",sans-serif;font-size:15px">Also in order to match this bandgap with the experimental value, I applied the U parameter. In unit-cell with different
U values, I got a variation in band gap that I am expecting but in supercell, bandgap remains the same, no variation observed.</span></div>
<div><span style="color:rgb(35,38,41);font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","Liberation Sans",sans-serif;font-size:15px">I'll be very thankful for any suggestions.</span></div>
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<div><font color="#232629" face="-apple-system, BlinkMacSystemFont, Segoe UI, Liberation Sans, sans-serif"><span style="font-size:15px">Thanks and regards,</span></font></div>
<div><font color="#232629" face="-apple-system, BlinkMacSystemFont, Segoe UI, Liberation Sans, sans-serif"><span style="font-size:15px">Poonam Sharma</span></font></div>
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<div dir="ltr">Poonam Sharma
<div>Research Scholar </div>
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