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Electronic and optical properties such as the density of states, dielectric function, absorption, reflectivity, loss function and refractive index of surface In x Ga 1−x P(0 0 1) are investigated first time with first principle methods based on plane-wave pseudo-potentials method within the LDA approximation in this paper, and the results show that the physical properties are much different from bulk materials. The physical properties of surface In 0.25 Ga 0.75 P is observed to be very different from In 0.5 Ga 0.5 P and In 0.75 Ga 0.25 P and the causes are analyzed in this paper. An indium-gradient surface In x Ga 1−x P structure has been calculated first time as well, and small differences in electronic and optical properties are found from In 0.5 Ga 0.5 P and indium-gradient structures except for x = (0.75, 0.25, 0.5), by which a new way is found to improve the physical properties with a given indium composition. [ABSTRACT FROM AUTHOR]

[Display omitted] • Anti-perovskites which are electron reversals of perovskite derivatives are popular with researchers as a novel functional material. • The anti-perovskite oxides and nitrides are an important part of the anti-perovskite family and also have a wealth of physical properties. • So far studies of anti-perovskite oxides and nitrides have mainly used first-principles calculations and experimental confirmation. • There are not many methods for the preparation of anti-perovskite nitrides and oxides. However, they have been successfully prepared and there is reason to believe that this substance will be of great help for a variety of future applications. In recent years, perovskites of the general formula ABX 3 have attracted many researchers to study due to their enriched nature and structure features. Anti-perovskites which are electron reversals of perovskite derivatives are popular with researchers as a novel functional material. Anti-perovskites have unique structures and thus exhibit many unconventional physical and chemical properties. Anti-perovskite oxides and nitrides are an essential part of anti-perovskites and research into them is in its infancy and a comprehensive review is urgently needed to generate interest. This paper provides an overview of the structural characteristics and specific properties as anti-perovskite nitrides and oxides, including superconductivity, optical properties, ionic conductivity, thermoelectric properties and narrow band gap semiconductor properties. In addition, the paper describes some of the possible methods available at this stage for preparing anti-perovskite oxides and nitrides and predicting some applications that could serve the future. With more enthusiasm, anti-perovskite oxides and nitrides will hopefully become an auspicious functional material. [ABSTRACT FROM AUTHOR]

[Display omitted] In order to create optoelectronic devices, it is essential to have access to semiconductors with a suitable bandgap, especially those with excellent optical properties that can be electronically tuned. In this paper, we constructed vertically stacked BlueP/SnS 2 heterostructures and systematically investigated their crystal structures and optoelectronic properties by first-principles computational methods. Our research shows that BlueP/SnS 2 is stacked vertically to create a type-II heterostructure with an indirect band gap of 0.802 eV, separating photogenerated electron-hole pairs effectively. Modifying the band gap of the heterostructure can be effectively achieved by applying biaxial strain and an electric field. The electric field affects the band gap linearly in the −0.5 to 0.5 V/Å range. Furthermore, the band gap reduces under tensile strain or compressive strain. Applying a biaxial strain of −10 % to the heterostructure changes the band alignment from type II to type I. At the same time, the applied electric field does not cause such a transition. Compared to BlueP and SnS 2 monolayers, BlueP/SnS 2 heterostructures exhibit redshift and blueshift in their absorption spectra. Redshift results from tensile strain or a weak electric field, while blueshift results from compressive strain or a strong electric field. The utilization of BlueP/SnS 2 heterostructures in nano- and optoelectronic devices shows excellent potential. [ABSTRACT FROM AUTHOR]

[Display omitted] First-principles molecular dynamics simulations were used to investigate pressure- and temperature-induced phase transitions in different TaN polymorphs. The driving forces and intermediate structures were established for the CoSn-like TaN (ε phase) to WC-type TaN (θ phase) and ε to NaCl type-TaN (δ phase) structural transformations that were observed in experiments and for the θ to hP4-194, θ to cP2-221, δ to cP2-221 and δ to tP4-129 phase transitions that were predicted in this investigation. Other possible TaN polytypes were systematically investigated and five new prospective phases were found: oP8-25, oP12-25, hP8-194, tP8-105 and tI8-109. All new structures are thermodynamically, dynamically and mechanically stable, and their formation energy is only slightly higher than that of the θ phase (by 0.014–0.032 eV/atom). The relative stability, electronic structure, chemical bonding, vibrational spectra, elastic moduli and their spatial anisotropy, Vickers hardness, fracture toughness, Debye temperature and optical properties (real and imaginary parts of the dielectric function, reflectivity spectrum) of the tantalum mononitrides mentioned above were systematically calculated and discussed. The oP12-25, tP8-105 and tI8-109 novel phases exhibit the Vickers hardness (33.1–34.2 GPa), fracture toughness (5.52–5.59 MPa m1/2) and Debye temperatures (609.7–616.1 K) that are higher compared to those of the known TaN structures. The TaN polytypes with the strong Ta-N bonds with minimal fraction of ionicity were found to possess the best mechanical properties. Further experimental investigations are highly desirable to confirm the results presented in this paper. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Structural, magnetic and optical properties of Mg-doped CeO 2 (1 1 1) surface were investigated. • The doped CeO 2 (1 1 1) surface systems exhibit different bonding character. • The doped surface and subsurface systems result in local and scattered spin atmosphere. • The incorporation of Mg can lead to the red shift of absorption edge. Abstract The electronic structure, magnetic and optical properties of Mg-doped CeO 2 (1 1 1) surface have been investigated by first-principles calculations. In this paper, the doping case is actively favorable to process under O-rich conditions than under Ce-rich conditions. The distortion of doping systems of Mg replacing Ce of surface is larger than that of subsurface. The covalent character is getting weaker and the ionic character is gradually obvious for Mg O bond from surface to subsurface doping. The results show that the existence of defect states with O 2 p orbital character makes spin splitting, causing the local and scattered magnetic moments for surface and subsurface doping of Ce, respectively. And the 9 and 12 atomic layers doping systems exhibit magnetic ground states with different magnetic moments. In particular, the calculated Curie temperature (about 434, 483, 1200 K) is higher than room temperature (RT), therefore, the theoretical results showed that Mg-doped CeO 2 (1 1 1) thin films would can be obtained stable room temperature ferromagnetism (RTFM), which is beneficial to practical application. In addition, the optical properties show that all doped systems are capable of enhancing effective absorption of visible and near-infrared light. [ABSTRACT FROM AUTHOR]

The theoretical applications of hyperbolic metamaterials have generated excitement in multiple fields, particularly in super-resolution optics. In practice, however, the potential of HMMs has been limited by the shortcomings of their constituent parts. Primarily, these are high losses and instabilities in the metal component, which is typically gold or silver, and excessive thickness in both types of layers. In this paper, we use density functional theory to investigate BaMoO 3 -SrHfO 3 metamaterials. We predict that these are hyperbolic throughout the visible range and have the potential to mitigate many of these limitations, including a significant loss reduction. We also examine the accuracy of the effective-medium theory, which is used to predict the bulk optical properties of multilayered HMMs. [Display omitted] • New class of hyperbolic metamaterials based on a layered perovskite/perovskite structure. • Lower losses compared to current metal plasmonic materials like gold and silver. • Comparison of the results of first-principles calculations with those of the effective-medium theory for layered metamaterials. [ABSTRACT FROM AUTHOR]

Black phosphorus (BP) is a new two-dimensional (2D) material. It has received significant attention because of its great potential in the field of optoelectronics, which arises due to its low-dimensional effects. In this paper, the effect of bi-axial strain on the band structure of monolayer BP has been studied by using the first-principles method based on density functional theory (DFT). We find that the band gap range of monolayer BP can be moderately and effectively adjusted by external stress from 0 to 1.845 eV. Simultaneously, the direct band gap is maintained during the stretching process, which leads to a high electron mobility suitable for applications. Moreover, the compressive strain can result in a semiconductor–metal transition (SMT) with few-layer BP, whereas tensile strain only affects the band gap. Based on the electronic properties of monolayer BP, its optical properties are analyzed in detail, and the influence of strain—from a compressive strain of 12% to a tensile strain of 12%—on these properties is systematically discussed. It is found that the strain range and mode have a significant impact on the optical properties. In addition, the dielectric function and absorption spectra calculated along two different directions indicate that a significant optical anisotropy appears, giving a strong directionality dependence in the primitive and strained monolayer BP. It can be concluded that by applying external stress to monolayer BP, its optical properties can be readily controlled, which is beneficial for device applications. Furthermore, based on its direction-dependent response to the external stress, this behavior can also be used to detect the orientation of the deposited BP without the need for precise electron microscopy. [ABSTRACT FROM AUTHOR]

MoS2-WS2 thin layers with different deposition sequences and stacking configurations have been studied using first principles full potential linearized augmented plane wave method. The electronic and optical properties of ten atomic layers (in [0 0 0 1] direction) of MoS2-WS2 are reported in the present paper. Ten layers of MoS2-WS2, which are free from quantum size effects, show an indirect band gap which varies between 0.89 and 1.22 eV by engineering of the layering sequence and stacking configuration. Optical properties like absorption coefficients, dielectric tensors and refractive indices of bilayer and multilayer films of MoS2-WS2 are determined and are found to be different from the ten layers of MoS2 and WS2. Changes in the electronic and optical properties of multilayers have been elaborated in terms of interlayer and intralayer S-S distances. A comparison of absorption spectra deduced using the first principles calculations for Si and different combinations of multilayers of MoS2-WS2 show their applicability in optoelectronics and photovoltaic devices. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we have investigated the electronic, optical and mechanical properties of the Y2O3 crystal by first-principle calculations based on the density–functional theory. The generalized gradient approximation (GGA-PBE) and hybrid exchange–correlation functional (HSE06) are both used for comparative study. It is found that, the band gap of Y2O3 calculated by HSE06 method (6.0eV) is in good agreement with the experimental band gap data (5.5eV), and HSE06 gives better electronic structure description close to experiments. Then we calculate the elastic constants, and derive the corresponding properties i.e.; bulk, shear and Young’s moduli, and Poisson’s ratio. Our calculated elastic and mechanical properties correspond well with experimental data. Besides, we also obtain the equilibrium lattice and bulk modulus of yttria by fitting the Birch–Murnaghan equation of state. It is found that, the HSE06 well reproduce the experimental lattice parameters, equilibrium volume and bulk modulus of Y2O3. Based on the accurate described crystal and electronic structure and mechanical properties by HSE06 method, the optical properties of this material are also analyzed. [Copyright &y& Elsevier]

Abstract: The goal of this paper is to undertake a detailed first principle calculation of the structural, electronic and optical properties of Sn1− x Sb x O2. The results show that the stability of Sn1− x Sb x O2 in the full range of Sb content points to the probability of a continuous solid solution, where the increasing Sb content leads to volume expansion with different variation trends in the lattice constants. The increase of Sb concentration in the semiconductor–metal–semimetal transition occurs in consonance with the corresponding changes in its structural, electronic and optical properties. Two competing mechanisms play essential roles in this transition, namely; the many body effect and the atom disorder. Our calculations concur with previous X-ray diffraction, sheet resistance, resistivity and optical parameters detections. The studies present a practical way of tailoring the physical behaviors of Sn1− x Sb x O2 through the alloying technique. [Copyright &y& Elsevier]