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.

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.

Effects of N-doping concentration on the electronic structure and optical properties of N-doped β-Ga_2O_3

The electronic structures and the optical properties of N-doped β-Ga2O3 with different N-doping concentrations are studied using the first-principles method.We find that the N substituting O（1） atom is the most stable structure for the smallest formation energy.After N-doping,the charge density distribution significantly changes,and the acceptor impurity level is introduced above the valence band and intersects with the Fermi level.The impurity absorption edges appear to shift toward longer wavelengths with an increase in N-doping concentration.The complex refractive index shows metallic characteristics in the N-doped β-Ga2O3.

Three-Dimensional Normal Stress for Controlling Electronic Structure and Magnetic Property of Fe2Ge

A system study of the three-dimensional normal stress for regulating electronic structure and magnetic property of Fe_2Ge is studied. The density states of Fe more than 92% contribution come from Fe 3d,the density states of Ge mainly contributed from Ge 4p and Ge 4s,and the Fe 3d spin induces the Ge 4p electron transfer. The inductive effect increases germanium electron energy,weakens the Fe spin density of states,opposes the stability of the ferromagnetic state. The magnetic moment varies from 5 to 3 μB with the stress charges from-30 to 30 GPa. The charge of Fe is negative whereas the Ge atom is positively charged,the Fe atom loses charge,the charge transfers to the Ge atom. The unevenly distributed charge forms the newoccupy state and spin polarization state in the Fe_2Ge electron structure system. The Fe is the electron donor,the total electron is transferred to Ge,but the total numbers of gain electron and total numbers of lost electron are not equal,so the Fe_2Ge electron system may have hybridization between the Fe 3d state and Ge 4p state.The magnetic of Fe_2Ge mainly comes from the unoccupied Fe 3d orbital,the Fe 3d is positive spinpolarization state and the spin-polarization strength is decreased,the Ge 4p is negative spin-polarization state and the spin-polarization strength are increased. M oreover,electrons-spin polarization is relevant to the structure parameters of the Fe_2Ge system,and controls spin-polarized electronic behavior by means of adjusting ferromagnetic.

First-principles calculations on the electronic structure and optical properties of BaSi_2

The electronic structure,densities of states and optical properties of the stable orthorhombic BaSi2 have been calculated using the first-principle density function theory and pseudopotential method. The results show that BaSi2 is an indirect semiconductor with the band gap of 1.086 eV,the valence bands of BaSi2 are mainly composed of Si 3p,3s and Ba 5d,and the conduction bands are mainly composed of Ba 6s,5d as well as Si 3p. The static dielectric function ε1(0) is 11.17,the reflectivity n0 is 3.35,and the biggest peak of the absorption coefficient is 2.15×105 cm-1.

Electronic and optical properties of Au-doped Cu_2O:A first principles investigation

The Cu2O and Au-doped Cu2O films are prepared on MgO （001） substrates by pulsed laser deposition. The X-ray photoelectron spectroscopy proves that the films are of Au-doped Cu2O. The optical absorption edge decreases by 1.6% after Au doping. The electronic and optical properties of pure and Au-doped cuprite Cu2O films are investigated by the first principles. The calculated results indicate that Cu2O is a direct band-gap semiconductor. The scissors operation of 1.64 eV has been carried out. After correcting, the band gaps for pure and Au doped Cu2O are about 2.17 eV and 2.02 eV, respectively, decreasing by 6.9%. All of the optical spectra are closely related to the dielectric function. The optical spectrum red shift corresponding to the decreasing of the band gap, and the additional absorption, are observed in the visible region for Au doped Cu2O film. The experimental results are generally in agreement with the calculated results. These results indicate that Au doping could become one of the more important factors influencing the photovoltaic activity of Cu2O film.

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.

Optical properties of anatase and rutile TiO2 studied by GGA+U

The optical properties of thermally annealed TiO_2 samples depend on their preparation process, and the TiO_2 thin films usually exist in the form of anatase or rutile or a mixture of the two phases. The electronic structures and optical properties of anatase and rutile TiO_2 are calculated by means of a first-principles generalized gradient approximation（GGA） ＋U approach. By introducing the Coulomb interactions on 3d orbitals of Ti atom（U^d） and 2p orbitals of O atom（U^p）, we can reproduce the experimental values of the band gap. The optical properties of anatase and rutile TiO_2 are obtained by means of the GGA＋U method, and the results are in good agreement with experiments and other theoretical data. Further, we present the comparison of the electronic structure, birefringence, and anisotropy between the two phases of TiO_2. Finally,the adaptability of the GGA＋U approach has been discussed.

Alkali-metal(Li, Na, and K)-adsorbed MoSi_(2)N_(4) monolayer: an investigation of its outstanding electronic, optical, and photocatalytic properties

Single-layer MoSi_(2)N_(4),a high-quality two-dimensional material,has recently been fabricated by chemical vapor deposition.Motivated by this latest experimental work,herein,we apply first principles calculations to investigate the electronic,optical,and photocatalytic properties of alkali-metal(Li,Na,and K)-adsorbed MoSi_(2)N_(4) monolayer.The electronic structure analysis shows that pristine MoSi_(2)N_(4) monolayer exhibits an indirect bandgap(E_(g)=1.89 eV).By contrast,the bandgaps of one Li-,Na-,and K-adsorbed MoSi_(2)N_(4) monolayer are 1.73 eV,1.61 eV,and 1.75 eV,respectively.Moreover,the work function of MoSi_(2)N_(4) monolayer(4.80 eV)is significantly reduced after the adsorption of alkali metal atoms.The work functions of one Li-,Na-,and K-adsorbed MoSi_(2)N_(4) monolayer are 1.50 eV,1.43 eV,and 2.03 eV,respectively.Then,optical investigations indicate that alkali metal adsorption processes substantially increase the visible light absorption range and coefficient of MoSi_(2)N_(4) monolayer.Furthermore,based on redox potential variations after alkali metals are adsorbed,Li-and Na-adsorbed MoSi_(2)N_(4) monolayers are more suitable for the water splitting photocatalytic process,and the Li-adsorbed case shows the highest potential application for CO_(2) reduction.In conclusion,alkali-metal-adsorbed MoSi_(2)N_(4) monolayer exhibits promising applications as novel optoelectronic devices and photocatalytic materials due to its unique physical and chemical properties.

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.