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This paper presents electronic spectrum calculations and a study of the optical properties of the binary compounds Mn70Al30 and Mn80Al20 with the β-Mn structure. The energy dependences of the calculated density of states, with high values at the Fermi level, are determined by broad bands formed by manganese 3d states. The calculated electronic structures are used to analyze measured optical conductivity spectra of the alloys in the quantum light absorption range. From their optical properties in the infrared spectral region, we evaluate a number of characteristics of conduction electrons. [ABSTRACT FROM AUTHOR]

In this paper, nanostructured tin oxide doped with Nitrogen was investigated by first principle calculations. At first, band structure, density of states, and projected density of states were evaluated for pure tin oxide. Then, the effect of doping with Nitrogen was studied for cases when N replaces O atom, Sn atom, respectively, and in two interstitials situation. Results were compared with pure reference case. Except of one interstitial case, Nitrogen doping usually plays the role of a p-type doping, however the decrease of band gap occurs in all cases. [ABSTRACT FROM AUTHOR]

Theoretical studies on CdS/BiOI heterojunctions are lacking; therefore, this paper studies their electronic structure and optical properties through density functional theory calculations. First-principles calculations were made to investigate the effect of introducing oxygen vacancy defects on the photocatalytic efficiency of CdS/BiOI. The band gap of CdS/BiOI was effectively narrowed compared to that of its constituent materials, resulting in a redshift of the absorption edge. Based on the obtained work functions, the difference in Fermi energy levels caused a spontaneous flow of electrons, resulting in band bending and the establishment of a local electric field. The electric field promoted the separation of electron–hole pairs. At the same time, the addition of oxygen vacancies created impurity levels, allowing light absorption to extend to the infrared region, further promoting carrier separation. Our study reveals the origin of the enhanced efficiency of CdS/BiOI heterostructures and also predicts the photocatalytic activity of CdS/BiOI heterojunctions after introducing oxygen vacancies. These results may facilitate the design of such structures with enhanced photocatalytic properties. • The electronic structure and optical properties of CdS/BiOI heterojunction are studied by using density functional theory, and the effect of introducing oxygen vacancy defects into the structure is predicted theoretically. • According to the band structure, density of state, 3D/2D charge density difference and work function calculated by the first principle, the electron transfer from BiOI to CdS can be analyzed, and the trend is enhanced after the introduction of oxygen vacancy defect. • The calculation of optical properties shows that the formation of heterojunction and the introduction of oxygen vacancy defects promote the enhancement of optical absorption intensity. • This paper supplements the theoretical calculation of vacancy in CdS/BiOI heterojunction. And defects are introduced into the heterostructure to enhance the catalytic performance of such materials. [ABSTRACT FROM AUTHOR]

The energy band structure, density of states, and optical properties of monolayers of MoS2 doped with alkaline earth metals (Be/Mg/Ca/Sr/Ba) are systematically studied based on first principles. The results indicate that all the doped systems have a great potential to be formed and structurally stable. In comparison to monolayer MoS2, doping alkaline earth metals results in lattice distortions in the doped system. Therefore, the recombination of photogenerated hole–electron pairs is suppressed effectively. Simultaneously, the introduction of dopants reduces the band gap of the systems while creating impurity levels. Hence, the likelihood of electron transfer from the valence to the conduction band is enhanced, which means a reduction in the energy required for such a transfer. Moreover, doping monolayer MoS2 with alkaline earth metals increases the static dielectric constant and enhances its polarizability. Notably, the Sr–MoS2 system exhibits the highest value of static permittivity, demonstrating the strongest polarization capability. The doped systems exhibit a red-shifted absorption spectrum in the low-energy region. Consequently, the Be/Mg/Ca–MoS2 systems demonstrate superior visible absorption properties and a favorable band gap, indicating their potential as photo-catalysts for water splitting. [ABSTRACT FROM AUTHOR]

This paper reports results from the study of the electronic structure, bonding and optical properties of ternary (HfC) m Al 4 C 3 (m = 1, 2, 3) carbides. The interatomic bonding and bond order is studied to elucidate the role to atoms in the structure. The band structures of all three (HfAl 4 C 4 , Hf 2 Al 4 C 5 and Hf 3 Al 4 C 6 ) carbides show conducting nature. All three carbides exhibit direct band gap. Density of states (DOS) spectra of HfAl 4 C 4 , Hf 2 Al 4 C 5 and Hf 3 Al 4 C 6 carbides reveal that the total number of states, N( E F ) at Fermi level are 2.84, 6.51 and 6.37 states/eV, respectively. The electronic charge transfer from Hf and Al atomic sites to C atomic site has been found in all three carbides. The bond order (BO) calculation of these carbides shows the dominating role of Al-C bonds in to the cohesion of crystal structures. Localization index (LI) calculation reflects highly delocalized states near the Fermi level. The dependence of dielectric function and optical conductivity on photon energy show anisotropic behavior of HfAl 4 C 4 , Hf 2 Al 4 C 5 and Hf 3 Al 4 C 6 carbides. [ABSTRACT FROM AUTHOR]

Based on the first-principles calculations, the electronic structure and optical properties of the Mo-doped monolayer rhenium disulfide (ReS2) model are calculated, and the system stability, bond length, charge difference density, band structure, photoabsorption coefficient, system stability, and reflectivity are analyzed. The calculation results show that doping changes the structural stability of the system, which gradually decreases with an increasing concentration of doping. The calculation of band structure and density of states indicated that the band gap value of the system decreases continuously to 0 with increasing doping concentration, while the average charge population of atoms at doping sites keeps increasing with the better electron-losing ability of atoms. Compared with the intrinsic monolayer ReS2, the peak of systemic reflectivity at different doping concentrations has corresponding degrees of redshift in a certain wavelength range, as demonstrated by the optical properties. [ABSTRACT FROM AUTHOR]

The structural, electronic, optical, and vibrational properties of B3N3H6 have been calculated by means of the first-principles density functional theory (DFT) calculations within the generalized gradient approximation (GGA) and the local density approximation (LDA). The calculated structural parameters of B3N3H6 are in good agreement with experimental data. The obtained band structure of B3N3H6 shows that it has an indirect band gap with 5.007 eV, indicating that it presents insulation characteristic. The total and partial density of states (DOS) of B3N3H6 are given, which tell us the states of the orbital occupation. With the band structure and density of states, we have analyzed the optical properties including the complex dielectric function, refractive index, absorption, conductivity, loss function, and reflectivity. By the contrast, it is found that optical anisotropy is observed in the (001) direction and (100) direction. Moreover, the vibrational properties have been obtained and analyzed, showing that B3N3H6 is dynamically stable due to that there is no imaginary frequency. The frequencies associating with the vibrations are given, which show that B3N3H6 has a low mechanical modulus and thermal conductivity. [ABSTRACT FROM AUTHOR]

Electronic and optical properties of δ-SnSe with different strains are investigated through first-principles calculations. It is shown that under a tensile strain, the band gap of δ-SnSe changes from indirect to direct, however its value remains the same. For comparison, when a compressive strain is applied, not only an indirect to direct transformation of the band gap is observed but also gradually reduction of its value to 1.26 eV. Further the density of electronic states is studied in these systems. The Sn p and Se p states at the bottom of the conduction band contribute to variations of the band structures. Moreover, the absorption strength in visible light has been enhanced due to the application of an external strain. These results show that the strained δ-SnSe might provide some potential applications in spintronic devices and optical fields. [ABSTRACT FROM AUTHOR]

The Li2CaTa2O7 compound belongs to the Ruddlesden-Popper family of layered perovskites. First principle approximation was used to investigate the electronic band structure and optical properties of the compound for three phases. Independent of the studied compound's structural type, Li2CaTa2O7 has semiconductor behavior and direct transition. In addition, the forbidden energy band gap of the compound decreases with rising temperature, as expected. Furthermore, the 3d orbital of Ca contributes to the conduction band due to the crystal field effect. Moreover, the optical response of the chosen axes of the compound to incoming electromagnetic rays varies with phase transition. [ABSTRACT FROM AUTHOR]

The structural, electronic band structure and optical properties of SnO2 and SnO2:F are investigated as a function of fluorine (F) concentration by first-principles calculation using PBE0 hybrid exchange-correlation functional. Various supercells were constructed and optimized corresponding to different F content. An increase in the lattice parameters is obtained with increasing F level. Two different Sn-F bond lengths behavior are observed, where one of them is more sensible to F concentration. Löwdin charge analysis, related to charge transfer of Sn(0), Sn (1), O(5) and F(5), is presented and discussed, including the contribution of empty orbits 5d and 4f from Sn atoms. SnO2:F materials display characteristics of the n-type semiconductor, occupied states contributed mostly from hybridized Sn 5s, Sn 5p, O 2s and O 2p states in the conduction band increase with an increase in F concentration. Density of states (DOS) diagram of SnO2:F shows a band gap-like behavior inside the conduction band. The F dependence of the direct band gap, optical band gap, band gap-like and Burstein-Moss shift are calculated and discussed. A high concentration of fluorine (around 16 at.%) shows a transformation from direct to an indirect band gap. The imaginary dielectric function presents intra-band transition around Fermi level corresponding to Drude´s electrons. Also, inter-band transitions from valence band to conduction band and from occupied conduction band to unoccupied conduction band are evident from the optical spectra. [ABSTRACT FROM AUTHOR]

The electronic structure of Ce1-xLaxPtIn is studied by means of ab initio full-potential local orbital basis (coherent potential approximation) (FPLO-CPA) and spin polarized relativistic Korringa-Kohn-Rostoker (SPRKKR- CPA) methods within the densities functional methodologies. In both methods, we have observed decrease of the density of states at the Fermi level versus of La concentration. The theoretical photoemission spectra of LaPtIn and CePtIn are compared with the experimental data and the agreement is good. We have also reported the optical properties of LaPtIn and CePtIn compounds obtained in GGA and GGA+U approximation. [ABSTRACT FROM AUTHOR]