Dear List, We are studying the Cu2O system with LDA+U theory (please see the last portion of the mail). We found that when we used a very LARGE U parameter for oxygen, Up, like 10000, Siesta still calculates the band energy and did not warn about its numerical values.
<sample setting> %block LDAU.proj Cu 1 # number of shells of projectors n=3 2 # n, l 10.000 0.000 # U(eV), J(eV) 0.000 0.000 # rc, \omega (default values) O 1 # number of shells of projectors n=2 1 # n, l 10000.00 0.000 # U(eV), J(eV) <== the Up,J 0.000 0.000 # rc, \omega (default values) %endblock LDAU.proj Physically, large, Up means a very large separation of the electronic states - so it should be avoided (pardon me If I am wrong in this case). *From the Log,* *Energies are (when Ud for Cu = 10. ev, Up = 10.eV):* siesta: Final energy (eV): siesta: Band Struct. = -472.209961 *Energies are (when Ud for Cu = 10. ev, Up = 10000.eV):* siesta: Final energy (eV): siesta: Band Struct. = -5730.637191 Corresponding band diagram is also attached. So will it be a better idea to have a warning message for very large U values for LDA+U calculations? Our other concern is, how one can systematically vary U? Can we use large values like Up=19, to fit an experimental band gap? with thanks and regards Krishna ***************************************************************************************************************************************** INPUT ******* SystemName Cu4O2 LatticeConstant 1.0 Ang %block LatticeVectors 4.287813 0.000000 0.000000 0.000000 4.287813 0.000000 0.000000 0.000000 4.287813 %endblock LatticeVectors NumberOfAtoms 6 NumberOfSpecies 2 %block ChemicalSpeciesLabel 1 29 Cu 2 8 O %endblock ChemicalSpeciesLabel AtomicCoordinatesFormat Fractional %block AtomicCoordinatesAndAtomicSpecies 0.250000 0.250000 0.750000 1 0.750000 0.250000 0.250000 1 0.250000 0.750000 0.250000 1 0.750000 0.750000 0.750000 1 0.500000 0.500000 0.500000 2 0.000000 0.000000 0.000000 2 %endblock AtomicCoordinatesAndAtomicSpecies %block kgrid_Monkhorst_Pack 8 0 0 0. 0 8 0 0. 0 0 8 0. %endblock kgrid_Monkhorst_Pack # Basis definition PAO.EnergyShift 200 meV PAO.SplitNorm 0.15 PAO.BasisSize DZ PAO.BasisType split XC.Functional LDA XC.authors PZ kgrid_cutoff 50. Ang MeshCutoff 250.0 Ry MaxSCFIterations 50 DM.MixingWeight 0.5 DM.NumberPulay 3 ElectronicTemperature 300 K #--------------------------------------------- LDA U # For an AFM-Type II structure, choose the following %block DM.InitSpin # Describe the initial magnetic order (on Ni only) 1 + 2 - 3 + 4 - 5 - 6 + %endblock DM.InitSpin DM.UseSaveDM .false. # Use DM Continuation files WriteIonPlotFiles .true. LDAU.FirstIteration .false. LDAU.ThresholdTol 1.0d-3 LDAU.PopTol 4.0d-4 LDAU.ProjectorGenerationMethod 2 LDAU.CutoffNorm 0.90 %block LDAU.proj Cu 1 # number of shells of projectors n=3 2 # n, l 10.000 0.000 # U(eV), J(eV) 0.000 0.000 # rc, \omega (default values) O 1 # number of shells of projectors n=2 1 # n, l 1000 0.000 # U(eV), J(eV) 0.000 0.000 # rc, \omega (default values) %endblock LDAU.proj #--------------------------------------------- LongOutput .true. WriteKpoints .true. WriteCoorXmol .true. WriteCoorStep .true. WriteCoorCerius .true. Diag.DivideAndConquer .false. WriteKbands T BandLinesScale ReciprocalLatticeVectors %block BandLines 1 0.0 0.0 0.0 \Gamma #Beginat\Gamma 22 0.0 0.5 0.0 X # 22 points from \Gamma to X 22 0.5 0.5 0.0 M # 22 points from X to M 33 0.0 0.0 0.0 \Gamma # 33 points from M to \Gamma 39 0.5 0.5 0.5 R # 39 points from \Gamma to R 33 0.0 0.5 0.0 X # 33 points from R to X %endblock BandLines ----------------------------------------------------------- For band diagram: please see https://drive.google.com/file/d/15eMlfLcAskPYdMAJ0f9xRC9SWt0w2BXF/view?usp=sharing
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