第一性原理计算N掺杂对InNbO4电子结构的影响

宽带隙（3.83 eV）半导体光催化材料InNbO4在紫外光作用下具有分解水和降解有机物的性能。最近实验发现了N掺杂InNbO4具有可见光下分解水制氢的活性。为了从理论上解释这一实验现象，本文采用基于密度泛函理论的第一性原理计算了N掺杂对InNbO4的能带结构、态密度和光学性质的影响。分析能带结构可得，N掺杂后在InNbO4的价带（O 2p）上方形成N 2p局域能级，导致电子跃迁所需的能量减小。吸收光谱表明，N掺杂后InNbO4的光吸收边出现了红移，实现了可见光吸收。     

Electronic transport study of PbSe pellets prepared from self-assembled 2D-PbSe nanostructures

This work presents a study of the electronic transport properties of PbSe pellets fabricated starting of PbSe nanostructures that exhibited a flake-like 2D morphology, which were synthesized by the co-precipitation method. Seebeck coefficient measurements revealed that the PbSe sample displays n-type conductivity, a maximum Seebeck coefficient of −512.6 μV/K around 380 K, and that the carriers scattering is dominated by acoustic and optical phonons. The Fermi level dependence on the temperature and the band gap energy are also reported. Interestingly, size-dependent confinement effects due probably to the reminiscent PbSe 2D character could be evidenced.     

Transport properties of mesoscopic graphene rings

Based on a recursive Green's function method, we investigate the conductance of mesoscopic graphene rings in the presence of disorder, in the limit of phase coherent transport. Two models of disorder are considered: edge disorder and surface disorder. Our simulations show that the conductance decreases exponentially with the edge disorder and the surface disorder. In the presence of flux, a clear Aharonov-Bohm conductance oscillation with the period Φ₀ (Φ₀=h/e) is observed. The edge disorder and the surface disorder have no effect on the period of AB oscillation. The amplitudes of AB oscillations vary with gate voltage and flux, which is consistent with the previous results. Additionally, ballistic rectification and negative differential resistance are observed in I-V curves, with on/off characteristic.     

First-principles study of new half Heusler for optoelectronic applications

We report investigations of the structural, electronic and optical properties of 36 half-Heusler compounds in comparison with II–VI semiconductors using the first-principles calculations based on the density functional theory. In this work, we demonstrate the similarity in the electronic structure of these materials with that of II–VI semiconductors through the analysis of lattice parameters, band gaps and static dielectric constants at ambient pressure. The evolution of these properties under pressure is also necessary to predict new candidates for the optoelectronic devices.     

Effects of lanthanides doping on the optical properties of graphene/WSe2 heterostructure based on ab-initio calculations

Based on the density functional theory, we discussed the electronic and optical properties of graphene/ WSe₂ (GW) heterostructure after lanthanides doping. Red shift appears and the optical parameter values are improved in the low energy region after the lanthanides are doped. Different doping types are also discussed. In the case of single doping, substitute Yb atom on W site will improve the peak values of the optical parameters greatly. In the case of co-doping, it is found that the effect will be more obvious when the two doped lanthanide atoms are located in the second neighboring positons. These results suggest that lanthanides doping does adjust the electronic structure and improve the optical properties of GW heterostructures, which providing useful guidance for the design of novel optical nanodevices based on two-dimensional materials.     

Structure and electronic properties of MNO3 (M: Li,Na, K,NH4) under pressure: DFT-D study

The structural and electronic properties of crystalline nitrates have been investigated within the framework of density functional theory including van der Waals interactions. Pressure behavior of nitrates has been investigated using semiempirical dispersion correction scheme DFT-D. The optimizations of the crystal structures have been done with full relaxation of the atomic positions and lattice parameters under the experimentally determined crystal symmetries. The pressure dependences of geometrical parameters, band gaps, densities of states, charge distributions, overlap populations and atomic charges are computed. The predicted results agree well with the available experimental data.     

Anomalous electronic transport in quasicrystals and related complex metallic alloys

We analyse the transport properties in approximants of quasicrystals α-AlMnSi, 1/1-AlCuFe and for the complex metallic phase λ-AlMn. These phases present strong analogies in their local atomic structures and are related to existing quasicrystalline phases. Experimentally, they present unusual transport properties with low conductivities and a mix of metallic-like and insulating-like characteristics. We compute the band structure and the quantum diffusion in the perfect structure without disorder and introduce simple approximations that allow us to treat the effect of disorder. Our results demonstrate that the standard Bloch–Boltzmann theory is not applicable to these intermetallic phases. Indeed their dispersion relations are flat, indicating small band velocities, and corrections to quantum diffusion, which are not taken into account in the semi-classical Bloch–Boltzmann scheme, become dominant. We call this regime the small velocity regime. A simple relaxation time approximation to treat the effect of disorder allows us to reproduce the main experimental facts on conductivity qualitatively and even quantitatively.     

Band gap engineering in silicene: A theoretical study of density functional tight-binding theory

In this work, we performed first principles calculations based on self-consistent charge density functional tight-binding to investigate different mechanisms of band gap tuning of silicene. We optimized structures of silicene sheet, functionalized silicene with H, CH₃ and F groups and nanoribbons with the edge of zigzag and armchair. Then we calculated electronic properties of silicene, functionalized silicene under uniaxial elastic strain, silicene nanoribbons and silicene under external electrical fields. It is found that the bond length and buckling value for relaxed silicene is agreeable with experimental and other theoretical values. Our results show that the band gap opens by functionalization of silicene. Also, we found that the direct band gap at K point for silicene changed to the direct band gap at the gamma point. Also, the functionalized silicene band gap decrease with increasing of the strain. For all sizes of the zigzag silicene nanoribbons, the band gap is near zero, while an oscillating decay occurs for the band gap of the armchair nanoribbons with increasing the nanoribbons width. At finally, it can be seen that the external electric field can open the band gap of silicene. We found that by increasing the electric field magnitude the band gap increases.     

Bronsted acid-mediated reactions of aldehydes with 2-vinylaniline and biphenyl-2-amine

Herein we report simple Bronsted acid-mediated reactions of aldehydes with 2-vinylaniline and biphenyl-2-amine. Ultimately, the useful nitrogen-containing heterocycle derivatives are obtained. The electronic properties of the substituents on the aldehydes and 2-vinylaniline were investigated. It was found that molecules with both electron-donating and -withdrawing substituents were perfectly suitable substrates for this transformation, and the expected products were obtained in moderate to excellent yields.     

Dependence of electronic and optical properties of multilayer SiC and GeC on stacking sequence and external electric field

The electronic and optical properties of different stacked multilayer SiC and GeC are investigated with and without external electric field (EEF). The band gaps of multilayer SiC and GeC are found smaller than that of monolayer SiC and GeC due to the interlayer coupling effect. When EEF is applied, the direct band gaps (ΔK–M) of multilayer SiC and direct band gaps (ΔK–K) of multilayer GeC all turn to indirect band gaps (ΔK–G) as the band at the G point drops dramatically toward zero. The imaginary part ε₂(ω)s of multilayer SiC and GeC show that new absorption peaks between 2–5 eV appear when the polarized direction is perpendicular to the layer plane, and new absorption peaks in infrared region appear as the EEF is higher than a certain point when the polarized direction is parallel to the layer plane. Our calculations reveal that different stacking sequences and EEF can provide a wide tunable band structures and optical properties for multilayer SiC and GeC.