First-principles investigations of structural, mechanical, electronic and optical properties of U_3Si_2-type AlSc_2Si_2 under high pressure

The structural, elastic, electronic and optical properties for U3Si2-type AlSc2Si2 compound under pressure were systematically investigated by using the first-principles calculations. The values of elastic constants and elastic moduli indicate that AlSc2Si2 keeps mechanical stability under high pressure. The mechanical properties of AISc2Si2 are compared with those of Al3Sc. The results indicate that AlSc2Si2 is harder than AI3Sc. Anisotropic constant AU and 3D curved surface of elastic moduli predict that AISc2Si2 is obviously anisotropic under pressure. The electronic structure of AlSc2Si2 exhibits metallic character and the metallicity decreases with the elevated pressure. In addition, optical properties as a function of pressure were calculated and analyzed. The present work provides theoretical support for further experimental work and industrial applications.

First-Principle Study on the Electronic Structure and Optical Property of New Diluted Magnetic Semiconductor(Y_(0.75)Ca_(0.25))(Cu_(0.75)Mn_(0.25))SO

The band structure,DOSs,and optical properties of(Y_(0.75)Ca_(0.25))(Cu_(0.75)Mn_(0.25))SO,including dielectric function,absorption function,reflection function,and energy loss spectrum were studied by using the first-principles calculation.The calculation results indicate that(Y_(0.75)Ca_(0.25))(Cu_(0.75)Mn_(0.25))SO is a direct bandgap semiconductor with a bandgap of 1.1 eV.The Fermi surface is asymmetric and exhibits spin splitting phenomenon.The new type of dilute magnetic semiconductor(Y_(0.75)Ca_(0.25))(Cu_(0.75)Mn_(0.25))SO exhibits significant light loss around 70 eV,with light reflection gradually increasing after 30 eV,and light absorption mainly occurring around 8-30 eV.These results also provide a basis for the discovery of more types of 1111 phase new dilute magnetic semiconductors in the future.

Electronic and optical properties of anion-doped c-ZrO_2 from first-principles calculations

Using the first-principles calculations based on density functional theory(DFT),the structure stability,electronic and some optical properties of C and N doped cubic ZrO2(c-ZrO2) in 24-atom systems were investigated.It is found from the formation energies calculations that N ions are easier to be doped into c-ZrO2 than C ions.The electronic structure results show that Zr8O15C and Zr8O15N systems are semiconductors with the band gap of 2.3 eV and 2.8 eV,respectively,which are lower than that of the pure ZrO2(3.349 eV).And optical properties results depict that anion doping,especially C adding,can enhance the static dielectric function,visible and ultraviolet light absorption and reflecting ability of c-ZrO2 crystal.

First-principles investigation of the effects of strain on elastic thermal, and optical properties of CuGaTe2

Based on the density functional theory, the influences of strain on structural, elastic, thermal and optical properties of CuGaTe2 are discussed in detail. It is found that the tensile strain on CuGaTe2 is beneficial to the decrease of lattice thermal conductivity by reducing the mean sound velocity and Debye temperature. Moreover, all strained and unstrained CuGaTe2 exhibit rather similar optical characters. But the tensile strain improves the ability to absorb sunlight in the visible range.These research findings can give hints for designing thermoelectric and photovoltaic devices.

Electronic structure and optical properties of Mg_xZn_(1-x)S bulk crystal using first-principles calculations

We perform the first-principles calculations within the framework of density functional theory to determine the elec- tronic structure and optical properties of MgxZnl-xS bulk crystal. The results indicate that the electronic structure and optical properties of MgxZnl_xS bulk crystal are sensitive to the Mg impurity composition. In particular, the MgxZnl-xS bulk crystal displays a direct band structure and the band gap increases from 2.05 eV to 2.91 eV with Mg dopant compo- sition value x increasing from 0 to 0.024. The S 3p electrons dominate the top of valence band, while the Zn 4s electrons and Zn 3p electrons occupy the bottom of conduction band in MgxZnl_xS bulk crystal. Moreover, the dielectric constant decreases and the optical absorption peak obviously has a blue shift. The calculated results provide important theoretical guidance for the applications of MgxZn1-xS bulk crystal in optical detectors.

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.

Uniaxial stress influence on lattice,band gap and optical properties of n-type ZnO:first-principles calculations

The lattice, the band gap and the optical properties of n-type ZnO under uniaxial stress are investigated by first- principles calculations. The results show that the lattice constants change linearly with stress. Band gaps are broadened linearly as the uniaxial compressive stress increases. The change of band gap for n-type ZnO comes mainly from the contribution of stress in the c-axis direction, and the reason for band gap of n-type ZnO changing with stress is also explained. The calculated results of optical properties reveal that the imaginary part of the dielectric function decreases with the increase of uniaxial compressive stress at low energy. However, when the energy is higher than 4.0 eV, the imaginary part of the dielectric function increases with the increase of stress and a blueshift appears. There are two peaks in the absorption spectrum in an energy range of 4.0-13.0 eV. The stress coefficient of the band gap of n-type ZnO is larger than that of pure ZnO, which supplies the theoretical reference value for the modulation of the band gap of doped ZnO.

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.

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.

Electronic Structure and Optical Properties of Zinc-Blende In_xGa_(1-x)N_yAs_(1-y) by a First-Principles Study

Electronic structure and optical properties of the zinc-blende InxGa1-xNyAs1-y system are calculated from the first-principles. Some relative simulations are performed using CA-PZ form of local density approximation in the framework of density functional theory. The supercell of intrinsic GaAs is calculated and optimized by using different methods, and the LDA-CA-PZ gives the most stable structure. The band gap of InzGa1-x As tends to decrease with the increasing In concentration. For the case of In0.0625Ga0.9375NyAs1-y, the band gap will show slight difference when N concentration is larger than 18. 75~. The optical transition of In dopant in GaAs exhibits a red shift, while it is a blue shift for the N dopant in InGaAs. Besides, dielectric function, reflectivity, refractive index and loss function in different doping model of InxGa1-xNyAs1-y are also discussed.

First-principles study of the structural,elastic,and optical properties for Sr_(0.5)Ca_(0.5)TiO_3

A detailed theoretical study of the structural, elastic, and optical properties for Sr0.5Ca0.5TiO3 is carried out by first- principles calculations. The band structure exhibits a direct bandgap of 2.08 eV at the F point in the Brillouin zone. The bulk modulus, shear modulus, Young＇s modulus, and Poisson＇s ratio are derived based on the calculated elastic constants. The bulk modulus B = 153 GPa and shear modulus G = 81GPa are in good agreement with available experimental data. Poisson＇s ratio v = 0.275 suggests that Sr0.sCa0.sTiO3 should be classified as being a ductile material. Using the electronic band structure and density of states, we analyze the interband contribution to the optical properties. The real and imaginary parts of the dielectric function, as well as the optical properties such as the optical absorption coefficient, refractive index, extinction coefficient, and energy-loss spectrum are calculated. The static dielectric constant ε1 （0） and the refractive index n（0） are also investigated.

The electronic,optical,and thermodynamical properties of tetragonal,monoclinic,and orthorhombic M_3N_4(M=Si,Ge,Sn):A first-principles study

A detailed study of the M_3N_4（M = Si,Ge,Sn） nitrides in their tetragonal,monoclinic and orthorhombic phases has been performed with the plane-wave pseudo-potential method combined with the quasi-harmonic approximation,including the phononic effects.We rationalize the main puzzle,i.e.,the fundamental properties of these phases are unclear,by calculating the crystal structures,density of states,and optical properties.The direct band gaps of t-Ge_3N_4,m-Si_3N_4,and o-Ge_3N_4 benefit the opto-electrical properties,t-,m-,and o-Si_3N_4 can be used as refractive materials while m-M_3N_4（M = Si,Ge,Sn） are optically transparent in the visible light region.Our results improve the understanding of the detailed electronic structures of all compounds,as well as the influences of electronic structure on their stabilities.Furthermore,we find that thermodynamic quantities are sensitive to structures and,therefore,depend on various temperature and pressure conditions.

First-principles study of the bandgap renormalization and optical property ofβ-LiGaO_(2)

Theβ-LiGaO_(2)with an orthorhombic wurtzite-derived structure is a candidate ultrawide direct-bandgap semiconductor.In this work,using the non-adiabatic Allen-Heine-Cardona approach,we investigate the bandgap renormalization arising from electron-phonon coupling.We find a sizable zero-point motion correction of-0.362 eV to the gap atΓ,which is dominated by the contributions of long-wavelength longitudinal optical phonons.The bandgap ofβ-LiGaO_(2)decreases monotonically with increasing temperature.We investigate the optical spectra by comparing the model Bethe-Salpether equation method with the independent-particle approximation.The calculated optical spectra including electron-hole interactions exhibit strong excitonic effects,in qualitative agreement with the experiment.The contributing interband transitions and the binding energy for the excitonic states are analyzed.

Linear optical properties of defective KDP with oxygen vacancy: First-principles calculations

The linear optical properties of potassium dihydrogen phosphate（KDP） with oxygen vacancy are investigated with first-principles density functional theory calculations. We use Heyd–Scuseria–Ernzerhof（HSE06） functional to calculate the linear optical properties because of its accuracy in the band gap calculation. Compared with the perfect KDP, we found that due to the defect states located at the band gap, the defective KDP with oxygen vacancy has new optical adsorption within the energy region from 4.8 eV to 7.0 eV（the corresponding wavelength region is from 258 nm to 177 nm）. As a result, the oxygen vacancy can decrease the damage threshold of KDP crystal. It may give a direction to the KDP production for laser system.

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.

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.

First-Principles Study of Electronic Structure and Optical Properties of Silicon/Carbon Nanotube

A supercell of a nanotube formed by a carbon nanotube (CNT) and a silicon nanotube (SiNT) is established. The electronic structure and optical properties are implemented through the first-principles method based on the density functional theory (DFT) with the generalized gradient approximation (GGA). The calculated results show that (6, 6) - (6, 6) silicon/carbon nanotubes (Si/CNTs) presented a direct band gap of 0.093 eV, (4, 4) - (6, 6) silicon/carbon nanotubes presented a direct band gap of 0.563 eV. The top of valence band was fundamentally determined by the Si-3p states and C-2p states, and the bottom of conduction band was primarily occupied by the C-2p states and Si-3p states in the Si/CNTs. It was found that (6, 6) - (6, 6) Si/CNTs have smaller energy band gap and better conductivity. Besides, Si/CNTs have satisfactory absorption characteristics and luminous efficiency in ultraviolet band.

Electronic Structure and Optical Properties of Antimony-Doped SnO_2 from First-Principle Study

A first-principles study has been performed to calculate the electronic and optical properties of the SbxSn1xO system.The simulations are based upon the method of generalized gradient approximations with the Perdew-Burke-Ernzerhof form in the framework of density functional theory.The supercell structure shows a trend from expanding to shrinking with the increasing Sb concentration.The increasing Sb concentration induces the band gap narrowing.Optical transition has shifted to the low energy range with increasing Sb concentration.Other important optical constants such as the dielectric function,reflectivity,refractive index,and electron energy loss function for Sb-doped SnO2 are discussed.The optical absorption edge of SnO2 doped with Sb also shows a redshift.

First-Principles Study of the New Layered Ternary Metal Telluride,Eu_(2)InTe_(5)

In this study,we performed first-principles calculations using the VASP(Vienna Ab initio Simulation)software package to investigate the crystal structure,electronic structure,and optical properties of a new layered ternary metal chalcogenide,Eu_(2)InTe_(5).Our results show that Eu_(2)InTe_(5) is a non-zero-gap metal with a layered structure characterized by strong intra-layer atomic bonding and weak inter-layer interaction,which suggests its potential application as a nanomaterial.We also studied the optical properties,including the absorption coefficient,imaginary and real parts of the complex dielectric constant,and found that Eu_(2)InTe_(5) exhibits strong photoresponse characteristics at the junction of ultraviolet and visible light as well as blue-green light,with peaks at wavelengths of 389 nm and 477 nm.This suggests that it could be used in the development of UV(ultraviolet)detectors and other optoelectronic devices.Furthermore,due to its strong absorption,low loss,and low reflectivity,Eu_(2)InTe_(5) has the potential to be used as a promising photovoltaic absorption layer in solar cells.

First-principle study of electronic structure and optical properties of Au-doped VO2

The electronic structure and optical properties of VO2 and Au-VO2 were studied using density functional theory. The calculation results show that the interaction between Au and O is stronger than that between V and O. There exists not only the covalent bonding but also ionic bonding in Au--O bond. The band gap of Au-VO2 is smaller than that of VO〉 while the dielectric constant, conductivity, and intensity of optical absorption of Au-VO2 are larger than those of VO2.