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<div style="font-size: 16px; font-family: Tahoma; color: rgb(0, 0, 0); font-weight: 400; font-style: normal;">For the following rule of thumb, I had implicitly assumed rectangular parallelepiped structure. For non-orthogonal lattice vectors one should use their proper perpendicular projections, say |b2,perpend|/|b1|, etc.</div>
<div style="font-size: 16px; font-family: Tahoma; color: rgb(0, 0, 0); font-weight: 400; font-style: normal;">Mahmoud</div>
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<div style="font-size: 16px; font-family: Tahoma; color: rgb(0, 0, 0); font-weight: 400; font-style: normal;">Dear Poonam,</div>
<div style="font-size: 16px; font-family: Tahoma; color: rgb(0, 0, 0); font-weight: 400; font-style: normal;">Hi.</div>
<div style="font-size: 16px; font-family: Tahoma; color: rgb(0, 0, 0); font-weight: 400; font-style: normal;">For having a uniform k-mesh in the reciprocal space, one has to respect the following rule of thumb:</div>
<div style="font-size: 16px; font-family: Tahoma; color: rgb(0, 0, 0); font-weight: 400; font-style: normal;">1- For direct lattice vectors (a1, a2, a3) obtain the reciprocal lattice vectors (b1, b2, b3).</div>
<div style="font-size: 16px; font-family: Tahoma; color: rgb(0, 0, 0); font-weight: 400; font-style: normal;">2- By finding the ratios |b2|/|b1| and |b3|/|b1|, you will be able to choose the number of k-mesh in b2 and b3 directions if you have already chosen in b1 direction.</div>
<div style="font-size: 16px; font-family: Tahoma; color: rgb(0, 0, 0); font-weight: 400; font-style: normal;">HTH</div>
<div style="font-size: 16px; font-family: Tahoma; color: rgb(0, 0, 0); font-weight: 400; font-style: normal;"> </div>
<div style="font-size: 16px; font-family: Tahoma; color: rgb(0, 0, 0); font-weight: 400; font-style: normal;">Bests,</div>
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<div style="font-family: Tahoma; color: rgb(0, 0, 0); font-size: 16px; font-weight: 400; font-style: normal;">Mahmoud Payami</div>
<div style="font-family: Tahoma; color: rgb(0, 0, 0); font-size: 16px; font-weight: 400; font-style: normal;">Physics & Accelerators Research School</div>
<div style="font-family: Tahoma; color: rgb(0, 0, 0); font-size: 16px; font-weight: 400; font-style: normal;">NSTRI, AEOI, Tehran, Iran</div>
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<div style="font-family: Tahoma; color: rgb(0, 0, 0); font-size: 16px; font-weight: 400; font-style: normal;">Email: mpayami@aeoi.org.ir</div>
<div style="font-family: Tahoma; color: rgb(0, 0, 0); font-size: 16px; font-weight: 400; font-style: normal;">Phone: +98 (0)21 82066504</div>
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<blockquote class="as91pFk8AX8sDPOUp66RUy8IoCRjefxNG8oLk8fg" style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">From: poonamsharma <poonamkaushik40@gmail.com><br />
To: Quantum ESPRESSO users Forum <users@lists.quantum-espresso.org><br />
Date: Thu, 11 Nov 2021 13:08:58 +0530<br />
Subject: Re: [QE-users] Different band gap in unitcell and in supercell<br />
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Dear Sir,</pre>
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>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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Thank you so much fr this suggestion.</pre>
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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>
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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>
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This 5X10X9 set is correct to to take although at 5X5X5 I obtained the convergence.</pre>
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Thank you so much once again.</pre>
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Thanks and regards,</pre>
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Poonam Sharma </pre>
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<div dir="ltr">Poonam Sharma
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<div class="gmail_attr" dir="ltr">On Sun, Nov 7, 2021 at 9:17 AM poonamsharma <<a href="mailto:poonamkaushik40@gmail.com">poonamkaushik40@gmail.com</a>> wrote:</div>
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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 should remain the same in the supercell.</span></div>
<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
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<div>Indian Institute of <span>Technology Bombay</span></div>
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