Structural, mechanical and electronic properties of nano-fibriform silica and its organic functionalization by dimethyl silane: a SCC-DFTB approach.

Self-consistent-charge density-functional tight-binding (SCC-DFTB) approximated method was employed to investigate the structural, mechanical and electronic properties of the zigzag and armchair nano-fibriform silica (SNTs) and their outer surface organic modified derivatives (MSNTs) with internal radii in the range of 8 to 36 Å. The strain energy curves showed that the nanotubes structures are energetically more stable compared to the respective sheet structures. External hydroxyl dihedral angles in silica nanotubes have small influence, about 0.5 meV.atom(-1), in the strain energy curve tendency of those materials favoring the zigzag chirality. The chemical modification of outer surface of SNTs by dimethyl silane group affects their relative stability favoring the armchair chirality in approximately 2 meV.atom(-1). MSNTs have axial elastic constants, Young's moduli, determined at the harmonic approximation, around 100 GPa smaller than the respective SNTs. The Young's moduli of zigzag and armchair SNTs are in the range of 150-195 GPa and 232-260 GPa, respectively. And for the zigzag and armchair MSNTs these values are in the range of 77-89 and 110-140 GPa, respectively. The SNTs and MSNTs were characterized as insulators with band gaps around 8-10 eV.