The splitting of band structure and absorption spectra, for silicon nanotubes (SiNTs) under axial magnetic field, are studied using the tight binding approximation. It is found that band splitting is approximately proportional to the magnitude of magnetic field as ΔEEg=νiiΦΦ0ΔEEg=νiiΦΦ0 where ν i i is the splitting rate. For Si g-NTs, we calculated the splitting rate of the two first bands nearest to the Fermi level in the Γ point and found that it can be fitted with a two degree polynomial as νii=∑2j=0aijxjνii=∑j=02ajixj where x=1n2x=1n2 and for sufficiently large diameter Si g-NTs, the ν i i can be fitted by a linear function. For semiconductor Si h-NTs the ν 11 = 6 but ν 22 and ν 33 show radial dependence. Also we found that applying magnetic field leads to splitting for all peaks in the low energy ranges for all zigzag Si h-NTs and Si g-NTs. The first peak of group (I) of Si g-NTs does not show any splitting in the magnetic field and for all metallic Si h-NTs, the magnetic field leads to creating a peak in the energy range less than 0.2 eV where this peak arises from energy gap created around Fermi energy.
