Dear Poonam, Hi.
For having a uniform k-mesh in the reciprocal space, one has to respect the following rule of thumb: 1- For direct lattice vectors (a1, a2, a3) obtain the reciprocal lattice vectors (b1, b2, b3). 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. HTH Bests, Mahmoud Payami Physics & Accelerators Research School NSTRI, AEOI, Tehran, Iran Email: mpay...@aeoi.org.ir Phone: +98 (0)21 82066504 -------------------------------------------------------- From: poonamsharma <poonamkaushi...@gmail.com> To: Quantum ESPRESSO users Forum <users@lists.quantum-espresso.org> Date: Thu, 11 Nov 2021 13:08:58 +0530 Subject: Re: [QE-users] Different band gap in unitcell and in supercell Dear Sir, >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. Thank you so much fr this suggestion. 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. 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. This 5X10X9 set is correct to to take although at 5X5X5 I obtained the convergence. Thank you so much once again. Thanks and regards, Poonam Sharma ------------------------------------------------------------------------------------------------- Poonam Sharma Research Scholar Department of Physics Indian Institute of Technology Bombay Mumbai - 400076 India. On Sun, Nov 7, 2021 at 9:17 AM poonamsharma <poonamkaushi...@gmail.com> wrote: Dear users, 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. Is this 1.75 eV is acceptable. 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. I'll be very thankful for any suggestions. Thanks and regards, Poonam Sharma ------------------------------------------------------------------------------------------------- Poonam Sharma Research Scholar Department of Physics Indian Institute of Technology Bombay Mumbai - 400076 India.
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