The optical properties of two kinds of single-wall silicon nanotubes (sw-SiNTs) [(n,0) and (n,n)] with small diameters are investigated by using the first-principles method.For these two kinds of nanotubes,the absorptive part ε"of dielectric functions exhibits a broad band from 4 to 8eV in the region of 4-1 leV,which is attributed to the transition of the π band to the π* and σ bands.Particularly,another small peak (inter-π band transition) at 1.2-2.3 eV in the low-energy region is also identified.In addition,the loss function of these nanotubes are calculated and discussed.
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