> I've watched/read some tutorials about QE, and some of these showed > that the occupation of semiconductors should be "smearing", other > ones that it should be "fixed",
The occupancies of metals and semiconductors should be "smeared" to obtain a good convergence of the calculation. In the plane-wave DFT calculation for the 'cyclic systems', we use desecrate k-point mesh where the occupancies of electrons may have decimal point if it cross the fermi-level (HOMO). > What value should I use for the SCF and electronic calculations of > the crystals that I'm going to work on (amino acids, hormones, > neurotransmitters, and drugs)? You should use the smearing method. > *Are there any differences when the molecule has a metal, like the Heme group? You also should use the smearing method in that case. You also should perform the spin polarized calculation for the molecule with a metal to check if there is no significant difference with the no-spin polarized calculation. > Besides, I would like to ask if there is a calculation that I could > perform to obtain the bandgap of these molecules. Is it only > possible if I create the band structure figure and calculate the > difference between the peaks in VB and CB? You can obtain a 'coarsely' estimated band gap by plotting the DOS after the scf calculation with the dense k-point mesh. If the value is significantly differ from that at the gamma point, the VBM-CBM (HOMO-LUMO) gap must be located at some k-point other than gamma. best regards kazume NISHIDATE 敬具 西館数芽 [email protected] [email protected] 2021年11月2日(火) 9:05 xavier neto via users <[email protected]>: > Dear Mahmoud Payami, > > Thank you for your answer. It helps me a lot. > > So, I can use the Fixed occupation and, if the energy levels show a small > bandgap, I introduce the Smearing. Is it right? > > > About the second question. I've read that the result of HOMO - LUMO, > obtained after the SCF calculation, can give the bandgap. Can I obtain the > bandgap in that way? If yes, I just have to add the nbnd function in the > input file? > On 11/1/21 02:04, Mahmoud Payami Shabestari wrote: > > Dear José Xavier, > Hi. > Smearing for the occupations is used when the levels near HOMO are so > close (commonly in metals near Fermi level) that in consecutive iterations > they may exchange positions and lead to nonconvergence. For semiconductors > with 3-5 eV gap I think it won't help. > Bests > Mahmoud Payami > NSTRI, AEOI, Tehran, Iran > > > > From: José Xavier via users <[email protected]> > <[email protected]> > To: "[email protected]" <[email protected]> > <[email protected]> <[email protected]> > Date: Mon, 1 Nov 2021 00:18:55 +0000 (UTC) > Subject: [QE-users] occupation in biological molecules and band gap > > Dear all, > > I'm new in QE. The group that I'm working with usually calculates the > properties of biologically relevant molecules, like amino acids, hormones, > neurotransmitters, and drugs, and I would like to introduce the QE code to > the group. Their previous papers have shown that the bandgap of these > crystals is something between 3-5 eV, which I understand to be in the > semiconductor range. > > I've watched/read some tutorials about QE, and some of these showed that > the occupation of semiconductors should be "smearing", other ones that it > should be "fixed", but no one showed calculations with this kind of > molecules. What value should I use for the SCF and electronic calculations > of the crystals that I'm going to work on (amino acids, hormones, > neurotransmitters, and drugs)? > > *Are there any differences when the molecule has a metal, like the Heme > group? > > Besides, I would like to ask if there is a calculation that I could > perform to obtain the bandgap of these molecules. Is it only possible if I > create the band structure figure and calculate the difference between the > peaks in VB and CB? > > Thank you for your help, > > Sincerely, > José Xavier > > _______________________________________________ > Quantum ESPRESSO is supported by MaX (www.max-centre.eu) > users mailing list [email protected] > https://lists.quantum-espresso.org/mailman/listinfo/users > > _______________________________________________ > Quantum ESPRESSO is supported by MaX (www.max-centre.eu) > users mailing list [email protected] > https://lists.quantum-espresso.org/mailman/listinfo/users
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