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Disagreement between bandgaps in band dispersion and DOS Date: 2022/08/12 04:51 Name: ELIE ALBERT   <elio-physics@live.com> Dear OPENMX users, I am trying to obtain the band structure (BS) and DOS of a nanotube I am working on. There is a mismatch in the bandgap values. From BS, the bandgap is clearly around 0.18eV, whereas the DOS is ~ 0 around the Fermi energy, with no apparent bandgap. What could have gone wrong? OBS: Since the nanotube is 1D, the band dispersion path is obligatorily defined as: Band.Nkpath 1 <Band.kpath 600 0.0 0.0 0.0 0.0 0.0 0.5 G Z Band.kpath> Regards Elio

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Re: Disagreement between bandgaps in band dispersion and DOS ( No.1 ) Date: 2022/08/12 12:04 Name: T. Ozaki Hi, Did you take long cell vectors perpendicular to the nanotube axis so that the interaction with copied images can be avoided? If you share your input file with us, we may be able to suggest definitely. Regards, TO Re: Disagreement between bandgaps in band dispersion and DOS ( No.2 ) Date: 2022/08/12 12:56 Name: ELIE ALBERT  <elio-physics@live.com> Dear Prof. Ozaki, Thanks for your reply. I did take large unit vectors along the x and y directions. Find below part of the input file: Atoms.UnitVectors.Unit Ang <Atoms.UnitVectors 31.000000000000000 0.000000000000000 0.000000000000000 0.000000000000000 31.000000000000000 0.000000000000000 0.000000000000000 0.000000000000000 23.002099999999995 Atoms.UnitVectors> # # SCF or Electronic System # scf.XcType GGA-PBE # LDA|LSDA-CA|GGA-PBE # DFT+U part # scf.Hubbard.U Off # On|Off, default=off #scf.Hubbard.Occupation dual # onsite|full|dual, default=dual #scf.DFTU.Type 2 # 1:Simplified(Dudarev)|2:General, default=1 #scf.dc.Type cFLL # sFLL|sAMF|cFLL|cAMF, default=sFLL scf.Slater.Ratio 0.625 # default=0.625 scf.Yukawa off # default=off ############## scf.SpinPolarization off # On|Off scf.SpinOrbit.Coupling off scf.partialCoreCorrection On scf.ElectronicTemperature 350.0 # default=300 (K) we probably need to converge scf.energycutoff 230.0 # default=150 (Ry) we need to converge scf.maxIter 6000 # default=40 scf.EigenvalueSolver band # Recursion|Cluster|Band scf.Kgrid 1 1 4 # means 4x4x4 we need to converge scf.Mixing.Type Rmm-Diis # Simple|Rmm-Diis|Gr-Pulay scf.stress.tensor on # off|on scf.Init.Mixing.Weight 0.70 # default=0.30 scf.Min.Mixing.Weight 0.01 # default=0.001 scf.Max.Mixing.Weight 0.10 # default=0.40 scf.Kerker.factor 10.0 # default=1.00 scf.Mixing.History 40 # default=5 scf.Mixing.StartPulay 40 # default=6 scf.criterion 2.0e-5 # default=1.0e-6 (Hartree) # # MD or Geometry Optimization # MD.Type Nomd # Nomd|Opt|DIIS|NVE|NVT_VS|NVT_NH MD.applied.pressure 0.004 # Can be values other than 0 to simulate systems under pressure. MD.maxIter 10000 # default=1 MD.Opt.StartDIIS 35 MD.TimeStep 0.05 # default=0.5 (fs) MD.Opt.criterion 5e-3 # default=1.0e-4 (Hartree/bohr) # # Band dispersion # # Voronoi.Charge off Band.dispersion on # on|off, default=off # if <Band.KPath.UnitCell does not exist, # the reciprical lattice vector is employed. Band.Nkpath 1 <Band.kpath 600 0.0 0.0 0.0 0.0 0.0 0.5 G Z Band.kpath> # # MO output # MO.fileout off # on|off num.HOMOs 1 # default=1 num.LUMOs 1 # default=1 MO.Nkpoint 1 # default=1 <MO.kpoint 0.0 0.0 0.0 MO.kpoint> # # DOS and LDOS # Dos.fileout on # on|off , default=off Dos.Erange -7.0 7.0 # default = -20 20 Dos.Kgrid 1 1 8 # default = Kgrid1 Kgrid2 Kgrid3 # # output Hamiltonian and overlap # HS.fileout off # on|off, default=off Regards Re: Disagreement between bandgaps in band dispersion and DOS ( No.3 ) Date: 2022/08/12 14:35 Name: T. Ozaki Hi, Did you try the gaussian broadening method with a small width instead of the tetrahedron method? If you see the gap using the gaussian broadening method, it indicates that the tetrahedron method failed to interporate the eigenenergies properly. This problem tends to happen especially for low dimensional systems. You may change the number of 8 in "Dos.Kgrid 1 1 8" to a larger number, and see what happens with the tetrahedron method. Also, you can check the standard output to make sure that the system is really treated as an one-dimensional system in your calculation. In this case, you must see the following message in the standard output. <Check_System> The system is chain. Regards, TO Re: Disagreement between bandgaps in band dispersion and DOS ( No.4 ) Date: 2022/08/12 21:21 Name: ELIE ALBERT  <elio-physics@live.com> Dear prof. Ozaki Once again, thanks for the feedback. The message "The system is a chain" is appearing in the std output. Regarding the DOS calculation, I am actually using the Gaussian smearing with a width of 0.035. Is that too large? I will try to use the tetrahedrom method and see what I will get. Regards Re: Disagreement between bandgaps in band dispersion and DOS ( No.5 ) Date: 2022/08/12 22:52 Name: T. Ozaki Hi, If you show us the full input file, we will be able to give a more definite point. Regards, TO Re: Disagreement between bandgaps in band dispersion and DOS ( No.6 ) Date: 2022/08/13 04:16 Name: ELIE ALBERT  <elio-physics@live.com> Dear Prof. Ozaki, I think the problem is solved. I have computed the DOS using different Gaussian broadening values, and I got the following: 0.0018 0.171eV 0.002 0.169eV 0.005 0.15eV 0.01 0.114eV 0.015 0.078eV 0.02 0.044eV ... Since the 0.0018 broadening gives the closest value of the bandgap to that obtained by the BS calculation, does it mean we can adopt the corresponding DOS? I have increased the DOS grid and there were no changes in the spectrum Regards

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