We present a systematic study of the geometric, electronic, and magnetic properties of hematite nanoribbons (α-Fe2O3NRs) using density functional theory. The hematite nanoribbons were generated by cutting atomically thin hematite nanosheets from the (110) and (104) surfaces along their [100] and [010] directions. All nanoribbon types are energetically feasible to synthesize. Nanoribbons obtained from the (110) surface show definite tunable semiconducting character. One type of nanoribbons obtained from the (104) surface shows surface modifications or bending nature indicating pseudo-Jahn-Teller effect, while the other type showed built-in oxygen vacancy on one edge despite preserving the stoichiometry, wherein the built-in oxygen vacancy introduces a half-metallicity into the nanoribbons at larger widths. The results indicate that α-Fe2O3NRs with the appropriate width and type are promising future materials in solar energy conversions and spintronics-based devices.

Using the spin-polarized density functional theory (DFT) and the DFT + U method, the geometric and electronic properties of the hematite α-Fe 2 O 3 (0001) film with the sulfur (S) atom doping and adsorption have been investigated systematically.The most stable hematite α-Fe 2 O 3 (0001) film with an anti-ferromagnetic arrangement is identified. For the study of sulfur adsorption on the film, the S adatom prefers to bond with three O atoms, in the center of a triangle formed by the three O atoms. The S acts as a cation at this site. The sulfur adsorption has introduced two gap states, in addition to the unoccupied surface states. Furthermore, with the most stable S-adsorption configuration, the diffusion of the S adatom from the surface to the inside is searched and the transition state along the minimum-energy pathway is also evaluated. For S-doping in the film, it is found that S substitution of O in the top layer is energetically favored than that in the deeper layer. It shows that the value of the band gap is reduced to ~1.26eV from ~1.43eV of the clean film. The formation energy of S substitution of O in the film is also obtained.

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A systematic, hybrid density functional theory study of interaction between SiGe nanotubes (SiGeNTs) and X (X = H, O, H2 and 02) have been performed using the hybrid functional B3LYP and an all electron 3-21G* basis set implemented in GAUSSIAN 09 suite of software. All possible internal. and external adsorption sites were considered, and it was found that H prefers to move onto top of an atom site while O prefers to incorporate into NT wall by breaking the bonds. Adsorption energies for H is ~2.0 eV and for O it is ~5.0 eV. Controlled adsorption of atomic H and several molecular O give rises to defect density states in the frontier orbital region. H rich adsorptions predict the difference between highest occupied molecular orbital (HOMO) energy and the lowest unoccupied molecular orbital (LUMO) energy increase while O rich adsorptions predict the decrease in HOMO-LUMO energy gap. O and O2 adsorptions predict definite ionic bonding character while H atomic adsorptions predict covalent bonding. H2 is very neutral towards the adsorption into SiGeNTs and clealy shows the physisorption adsorption. Considering the all adsorptions, the adsorptions happened within the Si vicinity of the SiGeNT shows the most stable and preferred adsorption region.

The geometric and electronic properties of the double-walled nanotubes (DWNTs), constructed by the two coaxial single-walled nanotubes (SWNTs) rolling the hexagonal titanium dioxide (TiO2) nanosheet along with the armchair (ac-) and the zigzag (zz-) directions, have been investigated systematically using the methods based on the density functional theory. For the optimized structures, the bandgap values of the TiO2 DWNTs are significantly reduced from that of the constituent SWNTs, falling in the visible light range. Further detailed analysis reveals that the reduction is caused by the band misalignment due to the different curvatures of the inner and outer TiO2 SWNTs.