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Context: The electronic properties and optical properties of Cr-doped monolayer WS2 under uniaxial compressive deformation have been investigated based on density functional theory. In terms of electronic structure properties, both intrinsic and doped system bandgaps decrease with the increase of compression deformation, and the values of the bandgap under the same compression deformation after Cr doping are reduced compared with the corresponding intrinsic states. When the compressive deformation reaches 10%, both the intrinsic and doped system band gaps are close to zero. New electronic states and impurity energy levels appear in the WS2 system when doped with Cr atoms. For the optical properties, the calculation and analysis of the dielectric function under each deformation regime of monolayer WS2 show that the compression deformation affects the dielectric function, and when the compression deformation is 10%, the un-doped and Cr-doped regimes show a decrease in ε1(ω) compared to the compression deformation of 8%. For each deformation system, the peak reflections occur in the ultraviolet region. Near the position where the second peak of the absorption spectrum appears, it can be seen that the ability of each system to absorb light gradually decreases with the increase of the amount of deformation and appears to be red-shifted to varying degrees. Methods: This study follows the initial principles of the density functional theory framework and is based on the CASTEP module of Materials-Studio software GGA and PBE generalizations are used to perform computations such as geometry optimization of the model. We have calculated the energy band structure of monolayer WS2 with intrinsic and compressive deformations of 2% and 4% using PBE and HSE06, respectively. The band gap values calculated using PBE are 1.802 eV, 1.663 eV, and 1.353 eV, respectively, and the band gap values calculated with HSE06 are 2.267 eV, 2.034 eV, 1.751 eV. The results show that the bandgap values calculated by HSE06 are significantly higher than those calculated by PBE, but the bandgap variations calculated by the two methods have the same trend, and the shape characteristics of the energy band structure are also the same. However, it is worth noting that the computation time required for the HSE06 calculation is much longer than that of the PBE, which is far beyond the capability of our computer hardware, and the purpose of this paper is to investigate the change rule of the effect of deformation on the bandgap value, so to save the computational resources, the next calculations are all calculated using the PBE. The Monkhorst–Pack special K-point sampling method is used in the calculations. The cutoff energy for the plane wave expansion is 400 eV, and the K-point grid is assumed to be 5 × 5 × 1. Following geometric optimization, the iterative precision converges to a value of less than 0.03 eV/Å for all atomic forces and at least 1 × 10−5 eV/atom for the total energy of each atom. The vacuum layer's thickness was selected at 20 Å to mitigate the impact of the interlayer contact force. [ABSTRACT FROM AUTHOR]

The monoclinic semiconductor GeP is a new class of Group IV–V layered material, and it shows attractive anisotropic optical and electronic properties. In this paper, we investigate the structural and electronic evolution of layered GeP under pressure, using in situ x-ray diffraction, Raman and infrared spectra, and the density functional theory. All characterization methods reveal that the pressure causes two obvious phase changes. One isostructural transition is observed around 6 GPa. Above 21 GPa, another crystalline-to-amorphous transformation is obtained. It is worth noting that the high-pressure amorphous state can be retained at ambient conditions after the pressure is released. In addition, the pressure-induced red-shift of absorbance edge suggests its bandgap decreases with pressure. This result indicates that pressure has a significant effect on GeP. Meanwhile, it also provides a method for obtaining amorphous GeP, which is of interest to the energy storage community as it is a potential anode material for lithium-ion batteries. [ABSTRACT FROM AUTHOR]

Summary: In this paper, we present the first principle investigations for structural and optoelectronic properties of pure, n‐type, p‐type, and co‐doped MgSiP2 chalcopyrite compounds. To examine the structural and optoelectronic response, density functional theory (DFT) as embodied in Wien2k method is utilized. Within DFT, we have considered the exchange correlation functional prescribed by Perdew‐Burke‐Ernerhof generalized gradient approximation and Tran‐Blaha modified Becke Johnson for all computation presented in this paper. The results obtained from present calculations are in well reconciliation with previously reported experimental and theoretical data for pure compound, which affirms the accuracy of present computations. The electronic responses of all compounds are investigated through the crystal structure, energy band structure, and density of states. Optical responses of studied compounds are explained in terms of dielectric tensor, absorption, reflectivity, and refractivity spectra. Drastic change in energy band gap from pure (2.04 eV) to co‐doped compound (0.30 eV) is observed. The obtained band gaps and absorption range confirm the utility of these compounds in photovoltaic application. [ABSTRACT FROM AUTHOR]

With the development of industrialization, the use of mercury in industry has become more and more widespread, causing serious impacts on the environment. It is therefore urgent to find new effective ways to combat mercury pollution. In this paper, The effect of C, O, P, Ni and Au doping on the adsorption of Hg atoms by WS 2 has been investigated based on the first nature principle of density functional theory. The electronic structures and optical properties of the adsorbed systems were calculated after atomic doping. The results show that the absolute value of the adsorption energy of the intrinsic adsorption system is small and does not favour the adsorption of Hg on WS 2. However, after C, P, Ni and Au doping, the adsorption energy of the system is significantly increased and a strong charge transfer between WS 2 and Hg atoms occurs, as well as a significant change in the band gap of the structure. This suggests that atomic doping favors the adsorption of Hg by WS 2. The effect of O doping on the adsorption system is not significant. In addition, a study of the optical properties revealed that the static dielectric constants of the system appeared to increase to varying degrees after the doping of the atoms. The doping of P, Ni and Au atoms increases the light absorption coefficient and contributes to the photocatalytic efficiency of the structures. The doped atoms cause a red shift in the reflectivity peak of the adsorbed system. In summary, the doping of C, P, Ni and Au enhances the adsorption of Hg atoms on WS 2. O doping has less effect on the adsorption of Hg on WS 2. • In this paper, the effect of C, O, P, Ni and Au doping on the adsorption of Hg atoms by WS2 was investigated. • The results show that atomic doping favors the adsorption of Hg by WS2. • Atomic doping alters the electronic properties of the structure. • Atomic doping alters the optical properties of the structure. [ABSTRACT FROM AUTHOR]

This paper employs the Heyd-Scuseria-Ernzerhof (HSE) function to research electronic structures of monolayer InxAl1-xN with different compositions (x = 0, 0.25, 0.5, 0.75, 1) based on the first-principles, and the optical properties of singlelayer InxAl1-xN are calculated by Generalized Gradient Approximation-Perdew Burke Ernzerhof (GGA-PBE) function. The influence of the electronic structure on the properties has been analyzed. Then the influence of doping quantity on the characteristics has been summarized, which also indicates the trend of the complex dielectric function and absorption spectrum. The calculation results show that with the increase of x, the static dielectric constant increases, the electron transition ability increases, and the absorption peak intensity in the light absorption spectrum increases. It can conclude that the InxAl1-xN compound can theoretically achieve the adjustable Eg and photoelectric performance with x, which will apply in making various optoelectronic devices, including solar cells and sensors. [ABSTRACT FROM AUTHOR]

Diamondoids are small diamond nanoparticles (NPs) that are built up from diamond cages. Unlike usual semiconductor NPs, their atomic structure is exactly known, thus they are ideal test-beds for benchmarking quantum chemical calculations. Their usage in spintronics and bioimaging applications requires a detailed knowledge of their electronic structure and optical properties. In this paper, we apply density functional theory (DFT) based methods to understand the electronic and optical properties of a few selected pure and modified diamondoids for which accurate experimental data exist. In particular, we use many-body perturbation theory methods, in the G0W0 and G0W0+BSE approximations, and time-dependent DFT in the adiabatic local density approximation. We find large quasiparticle gap corrections that can exceed thrice the DFT gap. The electron-hole binding energy can be as large as 4 eV but it is considerably smaller than the GW corrections and thus G0W0+BSE optical gaps are about 50% larger than the Kohn-Sham (KS) DFT gaps. We find significant differences between KS time-dependent DFT and GW+BSE optical spectra on the selected diamondoids. The calculated G0W0 quasiparticle levels agree well with the corresponding experimental vertical ionization energies. We show that nuclei dynamics in the ionization process can be significant and its contribution may reach about 0.5 eV in the adiabatic ionization energies. [ABSTRACT FROM AUTHOR]

In this paper, a CSVO3 phosphor for white LED has been successfully prepared by solid-state synthesis and has been characterized. The CsVO3 was simulated by Materials Studio software based on density functional theory (DFT). The results show that the CsVO3 sample has a direct optical transition with band gap energy of 3.143 eV. Under ultraviolet excitation in the range of 300–390 nm, the emission spectrum of CsVO3 phosphors ranges from 400 to 700 nm, and its peak emission spectrum is near 492 nm, and shows yellow color fluorescence emission. These results indicate that CsVO3 phosphor can be used as a promising white phosphor for white LED. [ABSTRACT FROM AUTHOR]

Using the density functional theory (DFT) of the first principle and Generalized gradient approximation method, the electronic structures and optical properties of the InxGa1-xN crystals with different x (x = 0.25, 0.5, 0.75, 1) have been calculated in this paper. The influence of the electronic structure on the properties has been analyzed. Then the influence of doping quantity on the characteristics has been summarized, which also indicates the trend of complex dielectric function, absorption spectrum and transitivity. With the increase of x, the computational result shows that the optical band gap (i.e.Eg) of the InxGa1-xN crystal tends to be narrow, then the absorption spectrum shifts to the low-energy direction. And the Fermi energy slightly moves to the bottom of conduction band which would cause the growth of conductivity by increasing x. In a word, the InxGa1-xN compound can be achieved theoretically the adjustable Eg and photoelectric performance with x, which will be used in making various optoelectronic devices including solar cell and sensors. [ABSTRACT FROM AUTHOR]

In the present paper, we have investigated the electronic structure of some sillenites - Bi12MO20 (M = Ti, Ge, and Si) compounds based on the density functional theory. The mechanical and optical properties of Bi12MO20 have also been computed. The second-order elastic constants have been calculated, and the other related quantities have also been estimated in the present work. The band gap trend in Bi12MO20 can be understood from the nature of their electronic structures. The obtained electronic band structure for all Bi12MO20 compounds is semiconductor in nature. Similar to other oxides, there is a pronounced hybridization of electronic states between M-site cations and anions in Bi12MO20. Based on the obtained electronic structures, we further calculate the frequency-dependent dielectric function and other optical functions. [ABSTRACT FROM AUTHOR]

In this work, the effects of x-value on electrical and optical properties was studied for the two dimensional (2D)GaAs1-xPxstructure by applying the density functional theory.We found that the gallium arsenide(GaAs) and gallium phosphide(GaP) monolayers are bound to each other, while the charge transfer between these two materialsleads to tuning the band gap value between 1.5 eV for GaAs to 2.24 eV for GaP. The density of state, band structure, and optical properties are investigated in this paper. [ABSTRACT FROM AUTHOR]

Functionalized MXenes have attracted great interest due to their unique electrical, magnetic, optical, and electrochemical properties. In this paper, the effect of interlayer coupling on the electronic structures of Ti 2 CO 2 MXenes is investigated by using density functional theory. Due to the interlayer coupling, the band structures of Ti 2 CO 2 nanosheet are split, generating an indirect band gap of 0.869 eV, which is smaller than that of Ti 2 CO 2 monolayer (1.044 eV). Biaxial strain can be used to achieve the transitions of direct-indirect-negative band gaps semiconductor. The interlayer interaction effectively inhibits the structural changes under stress, resulting that the band gap of nanosheet be adjusted in a large stress range. Furthermore, the change trend of imaginary part ε 2 of the dielectric function indicates that stress has an obvious regulatory effect on the optical transition. The different responses of monolayer and nanosheet under stress provides more choice for the optical devices of Ti 2 CO 2 MXenes. [ABSTRACT FROM AUTHOR]

In this paper, a systematic investigation of electronic structure and optical properties of quaternary chalcopyrite semiconductors Cu 2 ZnGeS 4 and Cu 2 ZnGeSe 4 in stannite and kesterite structures using the full-potential linearized augmented plane wave method are presented. The electronic structures and related properties of the crystals are studied with density functional theory using modified Becke – Johnson (mBJ) potential. The computed bands and density of states are found to be in good agreement with the available experimental and theoretical results. Important optical properties such as, dielectric functions, absorption spectra, refractivity and reflectivity of the crystals have also been investigated using the mBJ exchange potential. The imaginary parts of dielectric tensor are analyzed in terms of interband transitions. The band gap energies of stannite CuZnGeS 4 (CuZnGeSe 4) and kesterite CuZnGeS 4 (CuZnGeSe 4) compounds are obtained as 1.23 (0.74) eV and 1.52 (1.08) eV, respectively. Present band gap energies and optical parameters show feasibility of the studied materials in photovoltaic and other optoelectronic devices. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we investigate the electronic structure, optical and thermoelectric properties of the SrTiO 3 (STO) at a variant pressure from 0 to 120 GPa. The thermodynamic and structural stability has been confirmed by the enthalpy of formation and tolerance factor. The implementation of pressure has been found to shift the indirect bandgap to direct bandgap at 107 GPa to tune the optical and thermoelectric properties. The optical behavior of STO has been discussed by the dielectric constant and refraction of light in the visible and ultraviolet region. Furthermore, the thermoelectric behavior has been explored by investigating the electrical conductivity, thermal conductivity, See-beck coefficient and power factor. The thermal efficiency has been elaborated from the figure of merit, which shows the studied materials are highly valuable for energy device applications. [ABSTRACT FROM AUTHOR]

The I2-II-IV-VI4 series of quaternary chalcogenides semiconductors have drawn wide interest for their potential application as solar-cell absorbers. In this paper, we present a study of electronic and optical properties of the equilibrium kesterite structure (KS) of Cu2ZnGeS4 (CZGS) calculated by means of the full potential linearized augmented plane wave method. For this purpose, we used the Wien2k code based on the density functional theory with the generalized gradient approximation (GGA), modified Becke-Johnson exchange potential (mBJ) and the Hubbard potential U. The TB-mBJ is used alone or combined with U (TB-mBJ, and TB-mBJ+U). The results are compared with other theoretical results and the available experimental ones. The obtained results show that the top of the valence band is mainly composed by the Cu d orbital while the bottom of the conduction band is a mixture of Ge s and S p states. It was found that KS-CZGS has a direct band gap of 0.3, 1.8 and 2.0 eV using GGA, GGA+TB-mBJ and GGA+TB-mBJ+U, respectively. It is observed that states exist above the Fermi level (0 eV) with a width of 0.3 and 0.2 eV when we use GGA and GGA+TB-mBJ, while these states come down under the Fermi level when using GGA+TB-mBJ+U. The optical properties are calculated and an almost isotropic behavior is found in contrast to the reported properties of the stannite phase. This behavior can be linked to the charge density and the structure. [ABSTRACT FROM AUTHOR]

Based on the density functional theory, the effect of torsional deformation on the electronic structure and optical properties of boron nitride (BN)-doped graphene is studied by using the first-principles calculations. The band structure calculations show that the intrinsic graphene is a semi-metallic material with zero band gap and the torsional deformation has a large effect on its band gap, opening its band gap and turning it from the semi-metal to the medium band gap semiconductor. The doping of BN in graphene makes its band gap open and becomes a medium band gap semiconductor. When it is subjected to a torsional effect, it is found to have a weak influence on its band gap. In other words, the doping of BN makes the changes of the band gap of graphene no longer sensitive to torsional deformation. Optical properties show that the doping of BN leads to a significant decrease in the light absorption coefficient and reflectivity of the graphene at the characteristic peak and that of BN-doped graphene system is also weakened by torsional deformation at the characteristic peak. In the absorption spectrum, the absorption peaks of the doping system of the torsion angle of 2–20∘ are redshifted compared with that of the BN-doped system (the torsion angle is 0∘). In the reflection spectrum, the two reflection peaks are all redshifted relative to that of the BN-doped system (the torsion angle is 0∘) and when the torsion angle exceeds 12∘, the size relationship between the two peaks is interchanged. The results of this paper are of guiding significance for the study of graphene-based nanotube devices in terms of deformation. [ABSTRACT FROM AUTHOR]

In this paper, a brief retrospective review of the main developments in crystal field theory is provided. We have examined how different crystal field models are applied to solve the problems that arise in the spectroscopy of optically active ions. Attention is focused on the joint application of crystal field and density functional theory (DFT) based models, which takes advantages of strong features of both individual approaches and allows for obtaining a complementary picture of the electronic properties of a doped crystal with impurity energy levels superimposed onto the host band structure. [ABSTRACT FROM AUTHOR]

In this paper, the effects of Al doping and equibiaxial strain on monolayer h-BN were investigated by first-principles calculations. The results show that with tensile strain applied, the structure of the material is more stable, while the structural stability of the material decreases when compressive strain is applied. When the monolayer h-BN is doped with Al, the band gap decreases, and the higher the doped Al concentration, the lower the band gap. Equibiaxial strain is very effective for band gap tuning of monolayer h-BN. The optical calculation results show that the peaks of dielectric function and optical constant of the material decrease after Al doping, and the peaks decrease with the increase of Al concentration. When the strain is tensile, the optical properties of the material will be red-shifted as a whole, and the optical properties of the material will be blue-shifted when compressive strain is applied. After the monolayer h-BN was doped with two Al atoms and a strain of −9% was applied, the optical properties of the material were significantly affected. Our study provides some theoretical implications for the application of monolayer h-BN in the field of spintronic devices and optoelectronic devices. • The effect of equbiaxial strain and Al doping on monolayer h-BN were investigated. • Using first principles based on density functional theory. • Compared with the compression strain, the structure of the material is more stable under the tensile strain. • Band gap decreases with increasing Al doping concentration. • Optical properties of the material are red-shifted with tensile strain and blue-shifted with compressive strain. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the electronic and optical properties of MgO nanosheet in (100) and (111) directions. Our calculations carried out under the framework of density functional theory (DFT) exploiting WIEN2K code with Full potential, periodic boundary conditions, augmented plane-wave basis sets and GGA approximation. Electronic results indicate that MgO(111) nanosheet has an indirect band gap of 3.67 eV and MgO(100) nanosheet has a direct band gap of 3.14 eV. MgO(100) nanosheet exhibit more ionic bonding than MgO(111) and MgO(111) has more covalent bonding than MgO(100) nanosheet. Moreover, the optical results indicate that variation of dielectric function in x direction is more than the z direction. DOS and imaginary part of the dielectric function survey confirm semiconductor properties with different bang gap for structures. Comparing the imaginary part of dielectric functions in x and z directions for two structures, blue and red shift have been observed respectively. Our results indicate that these two nanostructures are transparent in a wide range of energy spectra and have low reflectivity. [ABSTRACT FROM AUTHOR]

In this paper, the structural, elastic, electronic and optical properties of double-perovskite halides Rb 2 CuBiX 6 are studied using first-principles calculations based on density functional theory. The results show that Rb 2 CuBiX 6 (X = Br, Cl) have thermodynamic and mechanical stability according to the tolerance factor, binding energy, formation energy and Born-Huang stability criterion. The B/G value and Poisson's ratio indicate that Rb 2 CuBiX 6 is a flexible material. Rb 2 CuBiBr 6 and Rb 2 CuBiCl 6 are indirect bandgap semiconductors with bandgap values of 1.11 eV and 1.43 eV, respectively. In addition, the effective masses of electrons of Rb 2 CuBiX 6 are much smaller than that of other perovskite compounds, indicating that they have better carrier mobility. In the visible light range, Rb 2 CuBiX 6 has good dielectric properties and excellent light absorption properties. Therefore, Rb 2 CuBiX 6 has great potential in photovoltaic application due to their suitable bandgap values and excellent optical properties. • The bandgap values of Rb 2 CuBiX 6 (X = Br, Cl) are very suitable for photosensitive materials of solar cells. • The Rb 2 CuBiX 6 can be a potential candidate for excellent light absorbing material. • Rb 2 CuBiX 6 is the structural and thermodynamic stabilities. [ABSTRACT FROM AUTHOR]

In this paper, we have calculated the structural, electronic, magnetic and optical properties of Sr2NiO3 and Sr2CoO3 using density functional theory (DFT) within generalized gradient approximation (GGA). The crystal structure of both materials is well described with Immm (No. 71) symmetry which are isostructural with Sr2CuO3 and both are quasi-one-dimensional (1D) rectangular lattice G-type antiferromagnets, in consistent with the experimental data. Due to a distortion, Sr2CoO3 lifts the near-degeneracy and states of the local Co electronic configuration, which demonstrates a strong coupling between the structural lattice and the electronic configuration. The calculated band structure shows a band gap of 1.376 eV for Sr2NiO3 and a band gap of 1.735 eV for Sr2CoO3. Ni and Co ions are in the high-spin and configurations with the magnetic moments of 1.585 and 2.587 , respectively. Based on the Heisenberg Hamiltonian model, we conclude that the superexchange intrachain TM-O-TM superexchange interaction is predominant and interaction between the 1D chains is weak. According to the calculated dielectric function, absorption spectrum and electron energy loss spectrum, the optical responses suggest that Sr2NiO3 shows the unique anisotropic structure and interaction of the application in optoelectronics. [ABSTRACT FROM AUTHOR]

In this paper, spin-polarized density functional calculations on the structural, electronic, optical and magnetic properties of the zincblende structure of the and alloys at in the ferromagnetic (FM) ordering has been investigated. The study is accomplished using the full-potential (FP) linearized augmented plane wave plus local orbital (LAPWlo) self-consistent scheme of calculations. To incorporate the exchange correlation component in the total energy calculations of the crystal, Perdew-Burke and Ernzerhof (PBE) parameterization for the generalized gradient approximation (GGA) and GGA U are employed. Basically, for both alloys, to address their structural properties, we calculated their equilibrium lattice constants, bulk moduli as well as pressure derivatives. In general, from the analysis of the obtained electronic band structure of these alloys, the half-metallic nature of and nearly half-metallic nature of the alloy are demonstrated. The plotted density of states (DOS) curves project spin-exchange splitting energy and as generated by V-3 d states. It has been clearly evident that the effective potential results for the spin-down case are more striking than for the spin-up case. In order to describe the magnetic behavior of these alloys, the exchange constants (valence band) and (conduction band) as well as the magnetic moment values are estimated. The calculated results of the magnetic moment show that the main source in the reduction of the local magnetic moment of V in the alloys in comparison with its free value is a - orbital hybridization and partial transfer to nonmagnetic sites of (Zn, S) and (Cd, S) in and alloys. In addition, a study concerning optical properties, such as the refractive index, reflectivity and absorption coefficients is performed to determine their potential for optical and optoelectronic devices. [ABSTRACT FROM AUTHOR]

This paper presents the effect of disorder on electronic, magnetic, and optical properties of CoCrZ (Z = Al, Si, Ga, Ge) Heusler alloy using density functional theory. Binary mixing is the most common form of atomic disorder in these compounds. We have considered three types of disorders: DO, A2, and B2 disorder which corresponds to X-Y, X-Z, and Y-Z mixing, respectively. After structural optimization, we found that A2 disorder has high formation energy and is most unlikely to occur. The half-metallic nature of the alloy is destroyed in the presence of DO and A2 disorder. The destruction of half-metallicity is due to reconstruction of energy states. B2 disorder retains the half-metallic nature of the alloy but spin-polarization value is reduced slightly as compared to the ordered alloy. In addition, the optical properties such as dielectric function, refractive index, absorption spectra, optical conductivity, reflectivity, and energy loss function of these alloys have also been investigated. [ABSTRACT FROM AUTHOR]

In this paper, the effect of Bi concentrations on the electronic structure, optical and thermoelectric properties was studied, using the density functional theory. The form of the generalized gradient approximation (GGA) proposed by Engel and Vosko (EVGGA) are used for the exchange and correlation potential. From the partial density of states, we find out that increasing the concentration of Bi results in a decrease of band gap of the compound. The PDOS of the InP compound elucidates that the valence bands are mainly comprised of P-p states, while the conduction band is mainly formed by foremost In-s and P-p with small contribution of P-s state while in InP/InB alloys the Bi-p stated strongly contribute in valance bands along with P-p states. From the calculated electronic structure we calculated the frequency dependent dielectric function along with other related optical constant. The transport coefficients are calculated using the semiclassical Boltzmann theory, as a function of temperature assuming a constant relaxation time. The Seebeck coefficient tended to decrease with increasing Bi content, whereas at low temperature figure of merit decreases with increasing the concentration of Bi. [ABSTRACT FROM AUTHOR]

To study electronic structures and optical properties of 6H-SiC, the lattice parameter, band structure, density of state, electron density difference and optical property of 6H-SiC are investigated by applying the first-principles density functional theory based on the plane wave pseudo-potential method in this paper. The results show that 6H-SiC is an indirect band gap semiconductor, and the valence band top is located at Γ, the conduction band bottom is located at (0, 0·50, 0·06) of M-L. The valence-band top is primarily from the hybrid of 2p states of C and Si atoms, while the conduction band bottom is mainly from the hybrid of C 2s and Si 3p states. The electron density differences indicate that the bond type of Si and C in 6H-SiC are sp3 hybridisation. The calculation results for optical properties show that there is an obvious dielectric peak within the range of energy from 0 to 15 eV, with absorption band edge corresponding to ultraviolet band, therefore, the 6H-SiC material may be a type of excellent ultraviolet semiconductor materials. [ABSTRACT FROM AUTHOR]

The ultrasoft pseudopotential planewave (UPPW) within density functional theory (DFT) has been used to investigate the electronic structure, optical, elastic and thermodynamics properties of newly binary boron nitride (T-B 3 N 3 ). The calculated lattice parameters are in good agreement with previous theoretical results and deviated are less than 0.4%. The electronic structure showed that the T-B 3 N 3 is metallic, and the optical spectra exhibit a noticeable anisotropy. The static dielectric constants, optical permittivity constants and the elastic properties are calculated. From our results, we observe that T-B 3 N 3 is mechanically unstable and ductile. The entropy, enthalpy, free energy, heat capacity and Debye temperature of T-B 3 N 3 was obtained. Up to now, there are no available experimental data about those properties. The results obtained in the present paper could provide important reference data for future studies. [ABSTRACT FROM AUTHOR]

Abstract: In this paper some structural, electronic and optical properties of BaF2 scintillator crystal have been calculated in cubic phase. Calculations were performed in DFT framework using FP-LAPW method and GGA and GGA+U approximations for exchange-correlation potential. In structural calculation part, optimum lattice constant and bulk modulus were calculated and these quantities are in good agreement with experimental and theoretical values. In electronic calculation part, energy band structure has been obtained along high symmetry points in k-space. Electronic and optical results with calculated energy gap by a semi-empirical method show that obtained energy gap of both GGA and GGA+U approximations is in good agreement with experimental values and band gap increases with increasing pressure. Also, in this work some optical properties of BaF2 compound such as dielectric function, energy loss function, optical conductivity and refractive index have been obtained. The peaks of optical conductivity are in good agreement with experimental results from reflectance spectroscopy of BaF2 compound. The obtained refractive index is in very good agreement with experimental values in the wavelength range 0.15–2.3μm. [Copyright &y& Elsevier]

In this paper, crystal structures, effective masses, electronic and optical properties of B 6 Ch (Ch = O, S, Se, Te) are studied within density functional theory (DFT). The band structures show that B 6 O, B 6 S and B 6 Se are semiconductors, while the zero-bandgap B 6 Te displays metallic properties. Moreover, the optical properties involving absorption coefficients, refractive index and extinction coefficients of B 6 Ch are shown and analyzed. The obtained results lead to a conclusion that B 6 Ch results in heavier effective masses and poor transparency. This is explained by the fact that the s orbitals of anion will cause lower dispersion of band edge and influence its positions. • Explore that B 6 O, B 6 S and B 6 Se are p-type TCO while B 6 Te is metal. • Offer evidence that chalcogen substitution narrow the band gaps of B 6 Ch. • Discover the dispersion of the top of the valence band affects its band edge position. [ABSTRACT FROM AUTHOR]

In this paper, electronic structures and third-order nonlinear optical (NLO) properties of a series of Pt-Pt bond-containing metal complexes have been calculated by using the density functional theory (DFT) combining with the sum-over-states (SOS) method. In order to check the reliability of this method, the electron correlations and basis sets have been compared. Our calculated results show that introduction of electron donor, thiophene ring and lengthing of organic conjugated ligand can enhance third-order NLO responses. The electronic structure analysis shows that the [Pt-Pt(H2P(CH2)PH2)2] fragment displays strong electron-withdrawing character in these systems. Meanwhile, the third-order NLO response of Pt-Pt bond also has been estimated by using TDDFT-SOS method. An enhancement of third-order NLO response has been observed because of the introduction of the Pt-Pt bond. This is mainly due to the intense and low-lying metal-to-ligand charge transfer (MLCT) and intraligand (IL) CT transitions. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we present the Compton profiles of Bi2S3 and Bi2Se3 using our 20 Ci 137Cs Compton spectrometer. To compare our experimental data, we have computed the Compton profiles, energy bands and density of states using linear combination of atomic orbitals with density functional theory (DFT) and Hartree-Fock (HF) scheme. It is seen that hybrid functional involving HF and DFT approximations gives a relatively better agreement with experimental momentum densities than other approximations of DFT. We have also reported the band structure, density of states, valence charge densities, dielectric functions and electron energy loss spectra using full potential linearized augmented plane wave scheme. On the basis of charge densities, Mulliken’s population data and equal-valence-electron-density profiles, Bi2S3 is found to be more ionic than Bi2Se3. The calculated dielectric functions for the parallel and perpendicular polarizations show a small anisotropic effect. The electron energy loss spectrum for Bi2Se3 is found to be in good agreement with the available experimental data. [Copyright &y& Elsevier]

Abstract: BC5 is a newly synthesized superhard material. We present a systematic investigation of optical properties of BC5 in P3m1 and I-4m2 phases at ambient and high pressure in the framework of density functional theory with the generalized gradient approximation (GGA) in this paper. Optical properties such as dielectric function, refractive index, absorption, reflectivity and electron energy-loss spectrum are obtained successfully. The feature in the spectra of the optical parameters is discussed. Through calculation, we find BC5 is optically anisotropic. Moreover, the dielectric function exhibits a large change at 70GPa pressure for P3m1 BC5 phase, but I-4m2 phase not, indicating the stable electronic structure that the I-4m2 phase possesses. [Copyright &y& Elsevier]

In this paper we studied the effects of the concentration of W as a doped atom on the V lattice site on the electronic and optical properties of tetragonal zircon-type B i V O 4 structure. The calculations were performed by the first-principles density functional theory WIEN2k code. The doping strategy was targeting V atoms substituted by W atoms using the same lattice parameters as pure B i V O 4 structure. To avoid the self interaction of impurities, the supercell method was adopted ensuring a sufficient length between the impurities in all directions. For all considered concentrations, the optical properties in the visible light range of λ ≥ 550 n m are improved over the undoped B i V O 4. Absorption spectra of the pure and doped tetragonal B i V O 4 with zircon-type structure. [Display omitted] • By increasing the concentration of W , the band gap energy is also increasing. • There is a small energy difference between the direct and indirect transition (abot 70 m e V). • By increasing the concentrations of W , the effective mass of electrons increases, while the effective mass of holes decreases. • For λ > 550 n m , the enhancement of the optical absorption coefficient by increasing the W concentration is clearly observed. [ABSTRACT FROM AUTHOR]

Gallium oxide (Ga2O3) is a promising wide-band-gap semiconductor material for UV optical detectors and high-power transistor applications. The fabrication of p-type Ga2O3 is a key problem that hinders its potential for realistic power applications. In this paper, pure α-Ga2O3 and Ca-doped α-Ga2O3 band structure, the density of states, charge density distribution, and optical properties were determined by a first-principles generalized gradient approximation plane-wave pseudopotential method based on density functional theory. It was found that calcium (Ca) doping decreases the bandgap by introducing deep acceptor energy levels as the intermediate band above the valence band maximum. This intermediate valence band mainly consists of Ca 3p and O 2p orbitals and is adequately high in energy to provide an opportunity for p-type conductivity. Moreover, Ca doping enhances the absorptivity and reflectivity become low in the visible region. Aside, transparency decreases compared to the pure material. The optical properties were studied and clarified by electrons-photons interband transitions along with the complex dielectric function's imaginary function. [ABSTRACT FROM AUTHOR]

In this paper, the HfS 2 monolayer electronic structure and optical properties under vertical strains are theoretically explored using density functional theory (DFT) calculations. The HfS 2 single layer dynamical stability is examined by calculating the phonon dispersion curves. Based on our simulation, the studied two-dimensional (2D) material is an indirect gap semiconductor with band gap value of 1.545 eV. The band gap engineering can be effectively realized by applying the vertical strains. In this regard, the indirect-direct gap transition in the monolayer at hand may be induced by compressive strains with strength from − 9%. Consequently, significant changes of the optical properties may be obtained, in particular when visible to middle ultraviolet regime radiation is incident on the sample. The HfS 2 monolayer displays promising optoelectronic applicability with a high absorption coefficient reaching to 49.600 (10 4 /cm) and 88.122 (10 4 /cm) in the visible and ultraviolet regime, respectively. Results may suggest an effective approach to modify the optoelectronic properties of the HfS 2 single layer at the time of designing its practical applications. [ABSTRACT FROM AUTHOR]

Pyrite is a mineral often associated with coal in coal seams and is a major source of sulfur in coal. Coal–pyrite is widely distributed, easily available, low-cost, and non-toxic, and has high light absorption coefficient. So, it shows potential for various applications. In this paper, the density-functional theory (DFT + U) is used to construct coal–pyrite with carbon doped in the sulfur and iron vacancies of pyrite. The effects of different carbon defects, different carbon doping concentrations, and different doping distributions in the same concentration on the electronic structure and optical properties of coal–pyrite were studied. The results show that the absorption coefficient and reflectivity of coal–pyrite, when its carbon atom substitutes the iron and sulfur atoms in the sulfur and iron vacancies, are significantly higher than those of the perfect pyrite, indicating that coal–pyrite has potential for application in the field of photovoltaic materials. When carbon is doped in the sulfur vacancy, this impurity state reduces the width of the forbidden band; with the increase in the doping concentration, the width of the forbidden band decreases and the visible-light absorption coefficient increases. The distribution of carbon impurities impacts the band gap but has almost no effect on the light absorption coefficient, complex dielectric function, and reflectivity, indicating that the application of coal–pyrite to photovoltaic materials should mainly consider the carbon doping concentration instead of the distribution of carbon impurities. The research results provide a theoretical reference for the application of coal–pyrite in the field of photoelectric materials. [ABSTRACT FROM AUTHOR]

• Based on DFT calculations, superlattices compounds have been investigated. • It is found that the gap of energy decreases with increasing the number of monolayer m (ZnTe). • The (ZnTe) m /(MnTe) n can therefore act as possible usefulness in optoelectronic applications. In this paper, we studied the structural, electronic, magnetic, and optical properties of (ZnTe) m /(MnTe) n superlattices with very small size layers (m - n : 1-1, 2-2, and 3-1). This work is purely theoretical and it's performed using the functional density theory (DFT) with the full-potential linear muffin-tin orbital (FP-LMTO) method implemented in the LmtART calculation code. We adopted the GGA + U formalism for the exchange-correlation potential. The obtained results demonstrate the existence of a strong correlation between the electronic, magnetic and optical properties of (ZnTe) m /(MnTe) n superlattices and their structural properties. In addition, and for more details on the behavior of these nanostructure systems, the density of states (DOS and PDOS), the s-d exchange constant (N 0 α) and the p-d exchange constant (N 0 β) are calculated and analyzed. The dielectric function ε(ω) is calculated for radiation energies up to 35 eV. The obtained results show that the static dielectric constant increases significantly with the increase in the number of monolayers m. [ABSTRACT FROM AUTHOR]

Using the first-principle calculation that is based on the density functional theory (DFT), our group gains some insights of the structural, electronic and optical properties of two brand new types of BiOI/TiO2 heterojunctions: 1I-terminated BiOI {001} surface/TiO2 (1I-BiOI/TiO2) and BiO-terminated BiOI {001} surface/TiO2 (BiO-BiOI/TiO2). The calculation illustrates that BiOI/TiO2 heterojunction has excellent mechanical stability, and it shows that there is a great possibility for the BiOI/TiO2 heterojunction to be used in visible-light range, hence the photocatalytic ability can be enhanced dramatically. Especially, from the calculation, we discovered that there are two specific properties: the band-gap of 1I-BiOI/TiO2 heterojunction reduces to 0.28 eV, and the BiO-BiOI/TiO2 semiconductor material changes to n-type. The calculated band offset (BOs) for 1I-BiOI/TiO2 heterojunction indicates that the interfacial structure contributes a lot to a suitable band alignment which can disperse the photo-generated carriers into the opposite sides of the interface, so this could effectively weaken the electron-hole recombination. Meanwhile, the built-in potential around the interface accelerates the movement of the photo-generated electron-hole pairs. We believe this is the reason that the BiOI/TiO2 material shows perfect photocatalytic performance. This paper can provide theoretical support for the related research, especially the further research of the BiOI-based material. [ABSTRACT FROM AUTHOR]

First-principles quantum mechanical computational methods are significant tools to understand the details of crystal structures which might be difficult through experimentation. In this paper, we have presented the electronic and optical properties of the thin film structure of Sb 2 S 3 in (001) orientation. Density functional theory based approaches are employed to determine the band structure, density of states (DOS), dielectric function and other optical parameters. Here, the investigations have been performed by full-potential linearized augmented plane-wave method (FP-LAPW) within the WIEN2k computational code. The band structure computations are done at the level of LDA-PW, PBE-GGA, PBE-GGA with SOC and PBE-GGA with mBJ potential, whereas for optical properties only PBE-GGA with mBJ potential was applied. Our calculations revealed that similar to optical properties, Sb 2 S 3 (001) oriented thin film had shown a reduction in the band gap energy than its counterpart bulk structure. This reduction, in the electronic and optical parameters, might be better understood in the course of quantum confinement effect for improving its performance for optoelectronics applications. [ABSTRACT FROM AUTHOR]

In this paper, the manipulative effect of N doping on topological insulator Bi 2 Se 3 was investigated by using density functional theory (DFT). The computational results reveal that the van der Waals (vdW) correction is necessary when calculating the geometric structure of Bi 2 Se 3. Taking into account the spin–orbit coupling(SOC), the electronic structure of Bi 2 Se 3 can be accurately described, especially for the energy bands near the Fermi level. The N doping at anion sites can produce an impurity band which appeared at Fermi energy. Comparing with pure Bi 2 Se 3 , the electronic structure of N doping Bi 2 Se 3 changed obviously at Fermi energy. The valence band and conduction band meet when N doped on Se1 sites, the insulating properties of Bi 2 Se 3 system are damaged. The indirect gaps between the valence band and conduction band are 0.135 eV and 0.115 eV with N doping on Se2 sites with the doping levels 6.67% and 1.67%, respectively. On the other hand, the N doping at Se sites of Bi 2 Se 3 can induce magnetic moments. The magnetic moments are related to the covalent bond length between N atom and Bi atom. Furthermore, the real and imaginary parts of dielectric functions have been computed. The static dielectric constant ε 1 (0) becomes significantly larger and the peaks in the imaginary part of dielectric constant ε 2 (ω) spectra move toward low energy. The intensity of the peak is gradually enhanced and there is a small bump in Bi 6 Se 8 N2 at 0.38 eV. The N doping paves a prospective way to tune the topological properties and may find change to potential spintronic applications and electronic devices. • The electronic structure of N doping Bi 2 Se 3 are changed obvious at fermi energy. • The insulation properties of Bi 2 Se 3 system are damaged with N doping on Se1 sites. • The N doping at Se sites can induce magnetic moments. [ABSTRACT FROM AUTHOR]