First-Principles Calculation on Geometric,Electronic and Optical Properties of Fully Fluorinated Stanene:a Large-Gap Quantum Spin Hall Insulator

The searches for large-gap quantum spin Hall insulators are important for both practical and fundamental inter- ests. In this work, we present a theoretical observation of the two-dimensional fully fluorinated stanene （SnF） by means of density functional theory. Remarkably, a significant spin-orbit coupling is observed for the SnF monolayer in the valence band at the F point, with a considerable indirect band gap of 278 meV. The direct gap of the SnF monolayer is at the F point, which is slightly larger by as much as 381 meV. In addition, the elastic modulus of the SnF monolayer is about 20J/m^2, which is comparable with the in-plane stiffness of black phos- phorus monolayer along the x-direction （~28.94 J/m^2）. Finally, the optical properties of stanene, SnF monolayer and stanene/SnF bilayer are calculated, in which the stanene/SnF bilayer is supposed to be an attractive sunlight absorber.

Electronic and optical properties of GaN–MoS2 heterostructure from first-principles calculations

Heterostructures(HSs)have attracted significant attention because of their interlayer van der Waals interactions.The electronic structures and optical properties of stacked GaN-MoS2 HSs under strain have been explored in this work using density functional theory.The results indicate that the direct band gap(1.95 e V)of the Ga N-MoS2 HS is lower than the individual band gaps of both the GaN layer(3.48 e V)and the MoS2 layer(2.03 eV)based on HSE06 hybrid functional calculations.Specifically,the GaN-MoS2 HS is a typical type-II band HS semiconductor that provides an effective approach to enhance the charge separation efficiency for improved photocatalytic degradation activity and water splitting efficiency.Under tensile or compressive strain,the direct band gap of the GaN-MoS2 HS undergoes redshifts.Additionally,the GaN-MoS2 HS maintains its direct band gap semiconductor behavior even when the tensile or compressive strain reaches 5%or-5%.Therefore,the results reported above can be used to expand the application of Ga N-MoS2 HSs to photovoltaic cells and photocatalysts.

Optical Properties of Filled Skutterudite ThFe_4P_(12)

加计算为 ThFe 4 在充满的 skutterudite 的 P 12 以便调查光性质并且显示出不同光转变的起源。乐队差距为 ThFe 4 P 12 。然后，不同转变山峰的贡献从绝缘的功能的想象的部分被分析。与最近的试验性的期望相对照，我们的计算在对试验性的思考系列和 ∈ 1(ω) 光谱的好同意。

First-principles investigations on the mechanical, thermal,electronic, and optical properties of the defect perovskites Cs_2SnX_6(X= Cl, Br, I)

The mechanical properties, thermal properties, electronic structures, and optical properties of the defect perovskites Cs2SnX6（X = Cl, Br, I） were investigated by first-principles calculation using PBE and HSE06 hybrid functional. The optic band gaps based on HSE06 are 3.83 eV for Cs2SnCl6, 2.36 eV for Cs2SnBr6, and 0.92 eV for Cs2SnI6, which agree with the experimental results. The Cs2SnCl6, Cs2SnBr6, and Cs2SnI6 are mechanically stable and they are all anisotropic and ductile in nature. Electronic structures calculations show that the conduction band consists mainly of hybridization between the halogen p orbitals and Sn 5s orbitals, whereas the valence band is composed of the halogen p orbitals. Optic properties indicate that these three compounds exhibit good optical absorption in the ultraviolet region, and the absorption spectra red shift with the increase in the number of halogen atoms. The defect perovskites are good candidates for probing the lead-free and high power conversion efficiency of solar cells.

First-principles study of the optical properties of defect electronic structure and chalcopyrite CdGa2Te4

The electronic and optical properties of the defect chalcopyrite CdGa2Te4 compound are studied based on the first- principles calculations. The band structure and density of states are calculated to discuss the electronic properties and orbital hybridized properties of the compound. The optical properties, including complex dielectric function, absorption coefficient, refractive index, reflectivity, and loss function, and the origin of spectral peaks are analysed based on the electronic structures. The presented results exhibit isotropic behaviours in a low and a high energy range and an anisotropic behaviour in an intermediate energy range.

Strain-tunable electronic and optical properties of h-BN/BC_(3)heterostructure with enhanced electron mobility

By using first-principles calculation,we study the properties of h-BN/BC_(3)heterostructure and the effects of external electric fields and strains on its electronic and optical properties.It is found that the semiconducting h-BN/BC_(3)has good dynamical stability and ultrahigh stiffness,enhanced electron mobility,and well-preserved electronic band structure as the BC_(3)monolayer.Meanwhile,its electronic band structure is slightly modified by an external electric field.In contrast,applying an external strain can mildly modulate the electronic band structure of h-BN/BC_(3)and the optical property exhibits an apparent redshift under a compressive strain relative to the pristine one.These findings show that the h-BN/BC_(3)hybrid can be designed as optoelectronic device with moderately strain-tunable electronic and optical properties.

First-principles studies of electronic,optical,and mechanical properties of γ-Bi2Sn2O7

The detailed theoretical studies of electronic,optical,and mechanical properties of γ-Bi2Sn2O7 are carried out by using first-principle density functional theory calculations.Our calculated results indicate that γ-Bi2Sn2O7 is the p-type semiconductor with an indirect band gap of about 2.72 e V.The flat electronic bands close to the valence band maximum are mainly composed of Bi-6s and O-2p states and play a key role in determining the electrical properties of γ-Bi2Sn2O7.The calculated complex dielectric function and macroscopic optical constants including refractive index,extinction coefficient,absorption coefficients,reflectivity,and electron energy-loss function show that γ-Bi2Sn2O7 is an excellent light absorbing material.The analysis on mechanical properties shows that γ-Bi2Sn2O7 is mechanically stable and highly isotropic.

Highly in-plane anisotropic optical properties of fullerene monolayers

Both the intrinsic anisotropic optical materials and fullerene-assembled 2D materials have attracted much interest in fundamental science and potential applications.The synthesis of a monolayer(ML)fullerene makes the combination of these two features plausible.In this work,using first-principles calculations,we systematically study the electronic structure and optical properties of quasi-hexagonal phase(qHP)ML and quasi-tetragonal phase(qTP)ML fullerenes.The calculations of q HP ML show that it is a semiconductor with small anisotropic optical absorption,which agrees with the recent experimental measurements.However,the results for qTP ML reveal that it is a semimetal with highly in-plane anisotropic absorption.The dichroic ratio,namely the absorption ratio of x-and y-polarized lightα_(xx)/α_(yy),is around 12 at photon energy of 0.29 eV.This anisotropy is much more pronounced when the photon energy is between 0.7 and 1.4 eV,whereα_(xx)becomes nearly zero whileα_(yy)is more than two orders of magnitude larger.This indicates qTP ML as a candidate for long-pursuit lossless metal and a potential material for atomically thin polarizer.We hope this will stimulate further experimental eforts in the study of qTP ML and other fullerene-assembled 2D materials.

Comparative study of Mo2Ga2C with superconducting MAX phase Mo2GaC： First-principles calculations

The structural, electronic, optical and thermodynamic properties of Mo2Ga2C are investigated using density func- tional theory （DFT） within the generalized gradient approximation （GGA）. The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. The electronic density of states （DOS） is calculated and analyzed. The metallic behavior for the compound is confirmed and the value of DOS at Fermi level is 4.2 states per unit cell per eV. Technologically important optical parameters （e.g., dielectric function, refractive index, absorption coefficient, photo conductivity, reflectivity, and loss function） are calculated for the first time. The study of dielectric constant （ε1） indicates the Drude-like behavior. The absorption and conductivity spectra suggest that the compound is metallic. The reflectance spectrum shows that this compound has the potential to be used as a solar reflector. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient of Mo2Ga2C MAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of Tc expression using available parameter values （DOS, Debye temperature, atomic mass, etc.） suggests that the compound is less likely to be superconductor.

Structural,Electronic,Optical and Thermodynamic Properties of Nanolaminated Boride Cr_4AlB_6

Density functional calculations were used to investigate the structural,electronic,optical and thermal properties of Cr_4AlB_6.The optimized lattice constants and atomic positions accord well with the experimental data.The analysis of band structure and density of states confirms the metallic nature of Cr_4AlB_6.The static dielectric constant e1（0） is about 128.0,and the maximum optical conductivity occurs at about 8.12 eV.In the photon energy range from 7.87 to 23.48 e V,Cr_4AlB_6 presents a metal reflective property.The plasma resonance frequency wp of Cr_4AlB_6 is at the photon energy of 23.85 eV,and Cr_4AlB_6 will be transparent and change from metallic to dielectric response if the incident light has frequency greater than the plasma frequency of Cr_4AlB_6.Thermodynamic properties including the primitive cell volume and thermal expansion,the bulk modulus and heat capacity Cv were further investigated with the increasing temperature and pressure by using the quasi-harmonic Debye model.

Optical property of amorphous semiconductor mercury cadmium telluride from first-principles study

The structural and optical properties of amorphous semiconductor mercury cadmium telluride (a-MCT) are obtained by the first principles calculations. The total pair distribution functions and the density of states show that the a-MCT has the semiconductor characteristic. The calculated results of dielectric function show that E2 peak of the imaginary of dielectric function for the crystal mercury cadmium telluride abruptly disappears in the amorphous case due to the long-range disorders. And the imaginary of dielectric function of a-MCT shows a large broad peak, which is in agreement with the available results of other amorphous semiconductors. From the linear extrapolation of the curve ωε 2(ω)1/2 versus ω, it can be obtained that the optical energy gap of amorphous semiconductor Hg0.5Cd0.5Te is 0.51±0.05 eV.

Structural, optical, and thermal properties of MAX-phase Cr2AlB2

First-principles calculations of the structural, optical, and thermal properties of Cr2AlB2 are performed using the pseudopotential plane-wave method within the generalized gradient approximation （GGA）. Calculation of the elastic constant and phonon dispersion indicates that Cr2AlB2 is mechanically and thermodynamically stable. Analysis of the band structure and density of states indicates that Cr2AlB2 is metallic. The thermal properties under increasing temperature and pressure are investigated using the quasi-harmonic Debye model. The results show that anharmonic effects on Cr^AlB~ are important at low temperature and high pressure. The calculated equilibrium primitive cell volume is 95.91 ~3 at T = 300 K, P - 0 GPa. The ability of Cr2AlB2 to resist volume changes becomes weaker with increasing temperature and stronger with increasing pressure. Analysis of optical properties of Cr2AlB2 shows that the static dielectric function of Cr2AlB2 is 53.1, and the refractive index no is 7.3. If the incident light has a frequency exceeding 16.09 eV, which is the plasma frequency of Cr2AlB2, Cr2AlB2 changes from metallic to dielectric material.

Mechanism for transmittance light tunable property of nanocrystalline Eu-doped SmB_(6):Experimental and first-principles study

Binary nanocrystalline rare-earth hexaboride is regarded as one of the promising optical absorption materials that possess the high transparency for visible light and the strong absorption for NIR due to the effects of localized surface plasmon resonance.In present work,we experimentally investigated the structural and optical absorption of ternary nanocrystalline Eu-doped SmB6 powder.As a result,it is found that the reaction temperature as an important factor not only refines the grain size,but also improves the powder dispersion of synthesized samples.The optical absorption results reveal that the transmittance wavelength of nanocrystalline SmB6 increases from 696 nm to exceeding 1000 nm with the Eu doping content increasing to x=0.8.Theo retically,in order to study the transmittance wavele ngth tunable mechanisms of nanocrystalline Eu-doped SmB6,the electronic structure,density of states and energy loss function were calculated by first-principle calculation.It shows that the En2+doping into SmB6 effectively reduces the plasma frequency excitation energy from 1.48 to 1.25 eV and leads to the transmittance wavelength redshift toward a higher wavelength.Based on above meaningful studies,present work is helpful for extension of optical applications of nanocrystalline SmB6 powder.

Secrets of high thermal emission of transition metal disilicides TMSi_(2)(TM=Ta,Mo)

TMSi_(2)(TM=Ta,Mo)are extensively used as thermal emissivity agents in high emission coatings due to their well-known"high"emissivity in infrared range.However,there is a paucity of the high temperature(HT)emissivity property of these two silicides.Moreover,room temperature(RT)spectrometer measurements have demonstrated that the emittance in infrared range of two silicides was considerably low.Therefore,providing critical HT data and satisfactory elucidation on the emission incompatibility of TMSi_(2)is eagerly needed.In this contribution,combining first principles calculations and Drude model,the reflectance spectra of TMSi_(2)were predicted at both RT and HT.Consistent with spectrometer measurements,the intrinsic emittance of silicides was relatively low in the entire investigated temperatures.To explain the incompatible emission behavior,two simplified models including the majority of high emissivity coating,SiO_(2),were proposed.Intriguingly,with SiO_(2)considered in simulations,no matter covered on the surface or blended in the composites,the emittance of the TMSi_(2)enhanced significantly.Our theoretical results demonstrate the non-negligible significance of oxides on the high temperature performance of silicides and provide the guidelines for improving the emission performance of silicides and searching for potential high emissivity agents.