I'm working with the Siesta DFT software, and managed to reproduce the band structure of bulk Si without any issues. However, when trying the same with a Si nanowire, the band structure looks nowhere near those published in literature (https://www.sciencedirect.com/science/article/abs/pii/S1386947705005345?via%3Dihub), and there doesn't seem to be any bandgap either. Has anyone had previous experience with a similar situation? Relevant figure from the article

Results from current calculations

SystemName      Si
SystemLabel     Si

NumberOfSpecies         1
NumberOfAtoms           85

%block ChemicalSpeciesLabel
  1  14  Si
%endblock ChemicalSpeciesLabel

LatticeConstant 5.41 Ang
%block LatticeVectors
  16.00  0.00   0.00
   0.00  1.00   0.00
   0.00  0.00  16.00
%endblock LatticeVectors

AtomCoorFormatOut  Ang
AtomicCoordinatesFormat Ang
%block AtomicCoordinatesAndAtomicSpecies
35.1650000000 0.0000000000 35.1650000000 1
36.5175000000 1.3525000000 36.5175000000 1
51.3950000000 2.7050000000 48.6900000000 1
50.0425000000 1.3525000000 50.0425000000 1
%endblock AtomicCoordinatesAndAtomicSpecies

%block kgrid_Monkhorst_Pack
   1  0   0  0.5
   0  16  0  0.5
   0  0   1  0.5
%endblock kgrid_Monkhorst_Pack

PAO.BasisSize           DZP
XC.functional           LDA      
XC.authors              CA       
SpinPolarized           .false.  
MeshCutoff              300 Ry   
kgrid_cutoff            100.0 Ang

MD.TypeOfRun       CG               
MD.VariableCell    true             
MD.NumCGsteps      50               
MD.MaxCGDispl      0.1 Bohr         
MD.MaxForceTol     0.01 eV/Ang      
MD.MaxStressTol    0.0001 eV/Ang**3 
%block GeometryConstraints          

%endblock GeometryConstraints

MD.UseSaveXV  true
MaxSCFIterations   100
DM.MixingWeight    0.01
DM.NumberPulay     3
DM.Tolerance       1.d-3
ElectronicTemperature  25 meV
SolutionMethod    diagon

BandLinesScale        pi/a
%block BandLines
1  0.0000000000 0.0000000000 0.0000000000 \Gamma
50 0.0000000000 1.0000000000 0.0000000000 Y
%endblock BandLines

%block WaveFuncKPoints
0.000 0.000 0.000 from 1 to 20
%endblock WaveFuncKPoints
  • $\begingroup$ We would need more information, can you show your band structure? I am assuming the ones in the post are from the literature. $\endgroup$ Sep 6 at 4:46
  • $\begingroup$ Hi @TristanMaxson, I have added the results from my calculations as the second image. The band structure is plotted from Gamma (x=0) to increasing K in the direction of the nanowire length. $\endgroup$
    – PBH
    Sep 6 at 8:35
  • $\begingroup$ Is the structure you are using the exact same one as in the reference you are comparing with? The band structures of nanomaterials can vary widely depending on the details of the structure, for example there exist both metallic and insulating carbon nanotubes. $\endgroup$
    – ProfM
    Sep 6 at 11:21
  • $\begingroup$ The one in the reference has the surface passivated with Hydrogen. However, as far as I found, this passivation is said to reduce the band gap (not eliminate at the considered diameters). And, since I use non passivated nanowires, the band gap should be either higher or at least comparable (I could be wrong as well). $\endgroup$
    – PBH
    Sep 6 at 12:20

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