Dear Poonam Sharma,
Regarding the convergence with respect to the k points mesh: I would suggest to have a look at the Quantum ESPRESSO input generator https://www.materialscloud.org/work/tools/qeinputgenerator 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. HTH Iurii -- Dr. Iurii TIMROV Senior Research Scientist Theory and Simulation of Materials (THEOS) Swiss Federal Institute of Technology Lausanne (EPFL) CH-1015 Lausanne, Switzerland +41 21 69 34 881 http://people.epfl.ch/265334 ________________________________ From: users <[email protected]> on behalf of poonamsharma <[email protected]> Sent: Thursday, November 11, 2021 8:38:58 AM To: Quantum ESPRESSO users Forum 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 <[email protected]<mailto:[email protected]>> 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.
_______________________________________________ Quantum ESPRESSO is supported by MaX (www.max-centre.eu) users mailing list [email protected] https://lists.quantum-espresso.org/mailman/listinfo/users
