I calculated the optical properties of bulk silicon by siesta-4.1b3. I used Optical.Scissor 0.45 eV to match my band gap. I found that the absorption coefficient starts from 2.5 eV instead of 1.1 eV (as compared to the experimental one). How can i found the correct absorption coefficient?
Hi,
I guess there are some parameters underconverged. For example, the Brillouin zone sampling is specified differently for SCF and Optical procedures. I would suggest plotting the density of states and check the DFT gap of silicon. It should be about 0.65 eV if the scissor-corrected gap should match the experimental one.
Hello
The band gap from band structure is found to be 0.65 eV but slightly less from DOS.
I am attaching my input file for your reference.
SystemLabel Si
NumberOfAtoms 2
NumberOfSpecies 1
%block ChemicalSpeciesLabel
1 14 Si
%endblock ChemicalSpeciesLabel
LatticeConstant 1.0 Ang
%block LatticeVectors
0.000 2.746415 2.746415
2.746415 0.000 2.746415
2.746415 2.746415 0.000
%endblock LatticeVectors
AtomicCoordinatesFormat Fractional
%block AtomicCoordinatesAndAtomicSpecies
-0.00001787 -0.00001787 -0.00001787 1 1 Si
0.25001797 0.25001797 0.25001797 1 2 Si
%endblock AtomicCoordinatesAndAtomicSpecies
PAO.BasisType split
PAO.BasisSize DZP
SolutionMethod diagon
PAO.SplitNorm 0.150000
PAO.EnergyShift 0.01 Ry
XC.functional GGA
XC.Authors PBE
SaveRho true
UseSaveData true
%block kgrid_Monkhorst_Pack
6 0 0 0.0
0 6 0 0.0
0 0 6 0.0
%endblock kgrid_Monkhorst_Pack
MeshCutoff 250 Ry
ElectronicTemperature 25 meV
MaxSCFIterations 300
DM.NumberPulay 7
DM.MixingWeight 0.0010000
MD.TypeOfRun CG
MD.NumCGsteps 0
MD.MaxCGDispl 0.100000 Ang
MD.MaxForceTol 0.010000 eV/Ang
#SpinPolarized true
WriteDM true
WriteCoorXmol true
WriteMDhistory true
DM.UseSaveDM true
MD.VariableCell true
OpticalCalculation .true.
%block Optical.Mesh
24 24 24
%endblock Optical.Mesh
Optical.OffsetMesh .true.
Optical.PolarizationType polarized
Optical.Scissor 0.45 eV
%block Optical.Vector
1.0 0.0 0.0
%endblock Optical.Vector
Optical.Broaden 0.2 eV
Optical.EnergyMaximum 20.0 eV
Optical.EnergyMinimum 0.0 eV