# Nanowire Band Structure using Siesta DFT

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?

SystemName      Si
SystemLabel     Si

NumberOfSpecies         1
NumberOfAtoms           85

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1  14  Si
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LatticeConstant 5.41 Ang
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AtomicCoordinatesFormat Ang
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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
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1  0   0  0.5
0  16  0  0.5
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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
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MaxSCFIterations   100
DM.MixingWeight    0.01
DM.NumberPulay     3
DM.Tolerance       1.d-3
ElectronicTemperature  25 meV
SolutionMethod    diagon

BandLinesScale        pi/a
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50 0.0000000000 1.0000000000 0.0000000000 Y
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• We would need more information, can you show your band structure? I am assuming the ones in the post are from the literature. Sep 6 at 4:46
• 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.
– PBH
Sep 6 at 8:35
• 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. Sep 6 at 11:21
• 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).
– PBH
Sep 6 at 12:20