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In the present work, using ab initio density-functional theory methods based on the Quantum ESPRESSO package, we have investigated the structural, elastic, electronic, and optical properties of 18-electron V2FeNiGe2 and Hf2FeNiSb2 double half-Heusler alloys. The calculated elastic properties suggest a ductile behavior with metallic bonding for V2FeNiGe2 and a brittle behavior with covalent bonding for Hf2FeNiSb2. The thermodynamic properties (Debye temperature, melting temperature) are also predicted and discussed for the studied alloys. The alloys are found to be semiconducting with indirect band gaps of 0.53 eV for V2FeNiGe2 and 0.47 eV for Hf2FeNiSb2. We also computed and analyzed their optical properties (dielectric function, optical conductivity, refractive index, absorption index, and reflectance) and our calculations suggest that both materials have high absorption coefficient and optical conductivity in the UV as well as visible region. The results make them potential candidates for the manufacture of opto-electronic devices. [ABSTRACT FROM AUTHOR]

First-principles calculations were carried out within the framework of density functional theory to investigate the influence of phase changes on the electronic and optical properties of CsSnI3. The lattice parameter and band gap of four different phases, i.e., α-, β-, γ-, and δ-phases, of CsSnI3 are estimated by employing different exchange–correlation functionals in order to explore their ability to reproduce geometric and electronic structures adequately. Comparison of the calculated total energies shows the non-perovskite orthorhombic (δ-phase) modification of CsSnI3 is the most stable, followed by the orthorhombic (γ-CsSnI3) perovskite phase. Thermal stability calculations in the form of temperature dependence of entropy as well as the absence of imaginary frequencies in the phonon dispersion diagrams also confirmed the dynamical stability of the δ-CsSnI3. The influence of the structural phase changes on the band gap and Fermi level shifts of CsSnI3 were assessed. Contribution of the electronic states on the formation of the valence and conduction band of four phases of CsSnI3 were determined, which were calculated using various exchange–correlation functionals, including the high-precision hybrid functional HSE06, and compared with available experimental ones. The calculated energy band distribution diagrams showed that all three perovskite modifications of CsSnI3 have direct transitions, while δ-CsSnI3 has an indirect transition. It was found that during the transition from δ- to α-phase, the Fermi level descends to the low energy region (towards the valence band), and the band gap decreases from 2.99 eV to 1.33 eV. During the transition from α- to β-phase, the band gap width again decreases to 1.23 eV and the Fermi level mixes by 1.65 eV towards the conduction band (CB). On the contrary, the band gap increases from β- to γ-phase and the Fermi level shifts by 0.41 eV towards the conduction band. The values of the complex dielectric constant and the refractive index of four phases of CsSnI3 were also calculated. [ABSTRACT FROM AUTHOR]

In this paper, a method based on density functional theory is used to replace varying numbers of sulfur atoms with carbon atoms in the original monolayer ZrS2 system, resulting in a new doped system. The theory is based on the First Principle. The photovoltaic properties of the new carbon-atom doping systems have been calculated and investigated. The pristine system and the carbon-atom doped systems were structurally optimized using the automatic optimization method. It was found that the stability of the structure decreases as the number of carbon atoms increases. Pristine monolayer 1T-ZrS2 is an indirect bandgap material. The results show that after doping carbon atoms in monolayer 1T-ZrS2, the p-type conductivity of the system increases and exhibits metallicity. The density of states analysis shows that the conduction band consists mainly of S-3p, Zr-4d, Zr-4p, Zr-5s and C-2p orbitals, while the valence band consists mainly of S-3p, S-3s, Zr-4d, C-2p and C-2s orbitals. It is concluded that strong hybridization between Zr-d and S-p orbitals is exhibited by both the pristine and doped systems. The analysis of the optical properties shows that the peak absorption coefficient and reflectivity peaks are blue-shifted in the doped system, and these peaks are lower than in the pristine system. The peaks of the real and imaginary parts of the dielectric function are also blue shifted. With the increase of doping concentration, the system’s energy loss decreases, indicating that proper doping can effectively reduce the system’s energy loss. The above studies provide theoretical support for applying ZrS2 in nano-optoelectronics. [ABSTRACT FROM AUTHOR]

The optoelectronic properties of ZnS doped with transition metals (Cu, Cd, Ag, and Au) are systematically investigated by applying first-principles computations based on the density functional theory (DFT). Various doping concentrations for Cu (5%, 10%, 20%), Cd (5%, 10%, 15%, 20%), Ag (5%, 15%), and Au (5%, 15%, 20%) are explored to examine their impact on the properties of ZnS. Our analysis confirms that all doped structures exhibit direct band gap semiconducting behavior. Notably, the band gap energy decreases with the incorporation of Cd, Ag, and Au, while an increase in Cu content results in a wider band gap. This work also evaluates how these transition metals influence the absorption coefficient, the dielectric constant, the refractive index, and the extinction coefficient of ZnS, providing a comprehensive insight into their effects. Our findings show a good agreement with existing experimental and theoretical data, offering a deep understanding of the optoelectronic properties of doped ZnS semiconductors. This investigation underlines the significance of doping in tailoring the properties of ZnS for enhanced optoelectronic applications, laying the groundwork for further experimental validation and theoretical analysis. [ABSTRACT FROM AUTHOR]

An intensive study on structural, electronic mechanical and optical properties of bulk Niobium Dichalcogenides NbX2 (X=S, Se) was carried out using the first principle. The structural parameters such as Equilibrium Lattice Parameters, Volume, Bulk Modulus, and FirstDerivative Modulus were calculated to determine if the materials are energetically stable. Elastic constants were further obtained from which mechanical properties i.e. bulk, Young's and shear moduli and consequently Poisson's ratio were obtained. Based on the well-known Born stability conditions Bulk-NbS2 is most likely mechanically anisotropic ductile material. While Bulk-NbSe2 for the predicted B/G ratio in all three methods is less than a critical value of 1.75, hence this shows that NbSe2 is a brittle material exploring its electronic and optical properties whose motivation was to find out the most stable phase and ascertain if these materials could be used in various fields that suit their mechanical and optical properties. Furthermore, from the calculated optical spectra, plasma frequencies were analyzed which indicated the possibility of applying the material in plasmonic-related fields.

Many novel materials with unique properties have been recognized in the two-dimensional (2D) materials family. The scientific community is investigating the suitability of these materials for possible applications. Using the density functional theory, the present work investigated the electronic, dielectric, and optical properties of four binary transition metal dichlorides (CdCl2, FeCl2, PdCl2, and ZnCl2) for their possible device applications. The electronic properties show that these are wide-bandgap materials. The optical and dielectric properties were studied in the incident photon energy range of 0–40 eV for the in-plane (parallel) and out-of-plane (perpendicular) light polarization directions. The optical analyses reveal that these are excellent absorbers of the incident light in the ultraviolet region of electromagnetic (EM) radiation, consistent with a high extinction coefficient for the corresponding incident photon energy. Moreover, these materials exhibit optical and dielectric anisotropy. It is observed that the PdCl2 is a biaxial optical birefringent material, whereas others are uniaxial. These are also good candidates for constructing reflection, transmission, and absorption edge/band filters in the different regions of the EM spectrum. Among these, the ZnCl2 exhibits excellent antireflective properties. Therefore, the present study shows the potential applications of these materials in electronic and optoelectronic devices. This study also provides a way to characterize them for further experimental analysis. [ABSTRACT FROM AUTHOR]

In this study, the structural, electronic, and optical properties of pristine graphene and graphene doped/co-doped with (N, Si) atoms are examined using a first-principles investigation. However, pristine graphene is characterized by a unique electronic structure known as the zero band gap (Eg = 0 eV), and this gap was opened up after the addition of N and Si substitutions, where it became 0.2, 0.21, and 1.38 eV for graphene doped with nitrogen, silicon and double doped with both (N, Si), respectively. For the band gap and the density of states, many parameters have been studied such as the complex dielectric function, conductivity, absorption spectra, loss function, and refractive index. The absorption curve shows two sharp peaks for all structures, where their intensities become lower and shift slightly towards lower energy after doping graphene with N, Si, and N-Si, indicating that this doping introduces additional energy states in the graphene band structure, making the transition between states easier to achieve. [ABSTRACT FROM AUTHOR]

One of the most interesting study areas in the renewable energy production is highly efficient water splitting that relies on the solar energy. More promising photocatalysts which can operate under irradiation from visible light are vitally required. Herein, based on the density functional theory, we demonstrated that two-dimensional SiH and β-SiTe monolayers exhibit indirect bandgap and suitable band edge locations for photocatalytic splitting of water. Using the PBE approach, we found that the bandgap values for the SiH and β-SiTe monolayer are 2.19 eV and 1.86 eV, respectively. The rectified bandgaps using the HSE06 function for SiH and β-SiTe were 2.93 eV and 2.43 eV, respectively. Surprisingly, photocatalytic property studies demonstrated that SiH and β-SiTe monolayers act as efficient photocatalysts for the production of hydrogen. Our outcomes emphasized that the highest peak of the absorption coefficient of SiH monolayer is 17.1 × 104 cm−1 in the UV region specifically at energy 7.90 eV. While β-SiTe monolayer has two peaks absorption of (13.5 × 104 and 8.1 × 104) cm−1 in the UV region at energies (7.18 and 9.22) eV. The results presented here imply that the SiH and β-SiTe could be useful in thermoelectric applications and the construction of photovoltaic cells and catalysts. [ABSTRACT FROM AUTHOR]

We have explored the electronic and optical properties of the stanene–BeO heterostructure using density functional theory (DFT), including van der Waals interaction using the DFT-D3 correction method of Grimme. The heterostructure exhibits a significant band gap opening, with 93 meV (PBE) and 141 meV (HSE06) values. The impact of spin–orbit coupling (SOC) has also been studied, with PBE + SOC exhibiting a band gap of 55 meV and HSE06 + SOC exhibiting a band gap of 71 meV. Using the DFT-1/2 method, various optical parameters of BeO and Sn monolayer and Sn-BeO heterostructure were studied. The results show a strong red shift in the absorption coefficient, extinction coefficient, and reflectivity, with a prominent absorption peak in the near-UV and visible regions. A significant second harmonic generation peak of 8 × 104 pm V−1 was also obtained. The excellent optical properties of the heterostructure indicate its potential for use in future optoelectronic devices. [ABSTRACT FROM AUTHOR]

This research explored the physical properties of AuMTe2 (M = Ga, In) chalcopyrite compound. We employ the full-potential linearized augmented plane wave (FP-LAPW) method in combination with the Tran-Blaha modified Becke–Johnson potential (TB-mBJ) as well as the generalized gradient approximation (GGA-PBE(96)), local density approximation (LDA) and Wu–Cohen generalized gradient approximation (WC-GGA) for the exchange–correlation potentials to analyze the structural, electronic and optical properties. The results are presented for lattice constant, bulk modulus, its pressure derivative, density of state (DOS) and optical properties. The structural and electronic outcomes obtained in this study align well with existing theoretical data. Our investigation revealed that the studied compounds exhibit a direct band gap, with average energy gaps of order of 0.281 eV for AuGaTe2 and 0.092 eV for AuInTe2 compounds, respectively. Optical properties, encompassing reflectivity R(w), absorption coefficient α(ω), refractive index n(ω), optical conductivity σ(ω), extinction coefficient k(ω) and energy loss function L(ω) are determined from real and imaginary parts of the computed dielectric function within the frameworks of the modified Becke–Johnson plus PBE-GGA(96), LDA and WC-GGA exchange–correlation potentials. The computed optical properties reveal minimal energy loss and reflectivity, alongside satisfactory absorption capability and optical conductivity within the infrared and visible spectral regions. These findings indicate potential applications in fields such as infrared absorption technologies and optoelectronic industries. This marks the initial quantitative theoretical forecast of the optical properties for these chalcopyrite compounds, necessitating experimental confirmation. [ABSTRACT FROM AUTHOR]

Photocatalytic materials are of great scientific interest due to their potential applications in sustainable energy sources. Band gap and optical absorption of the materials are two core characteristics for photocatalysis that eventually depend on electronic structure. In order to accurately compute (predict) the electronic‐scale properties of a crystalline solid using first principles calculations, which might be costly to measure experimentally, large‐scale atomic level calculation frameworks have been made possible through the use of density functional theory (DFT). We have used DFT with many body perturbation theory (MBPT) by solving the bethe‐salpeter equation (BSE) to priorly predict the properties of bulk tin sulfide (SnS) as it meets the necessary requirements for photocatalytic applications. We fixed the DFT band gap underestimation by including the Hubbard parameter (U) and used projector augmented wave pseudo‐potentials with generalized‐gradient approximation (GGA) to calculate the electronic and optical properties of SnS. Optical properties were computed using independent particle approximation (IPA) and BSE with DFT+U wave functions. Our theoretical results align with experimental data for this material, demonstrating the potential for further research in validating experimental results with theoretical approximations and empirical relations. [ABSTRACT FROM AUTHOR]

Photocatalytic materials are of great scientific interest due to their potential applications in sustainable energy sources. Band gap and optical absorption of the materials are two core characteristics for photocatalysis that eventually depend on electronic structure. In order to accurately compute (predict) the electronic‐scale properties of a crystalline solid using first principles calculations, which might be costly to measure experimentally, large‐scale atomic level calculation frameworks have been made possible through the use of density functional theory (DFT). We have used DFT with many body perturbation theory (MBPT) by solving the bethe‐salpeter equation (BSE) to priorly predict the properties of bulk tin sulfide (SnS) as it meets the necessary requirements for photocatalytic applications. We fixed the DFT band gap underestimation by including the Hubbard parameter (U) and used projector augmented wave pseudo‐potentials with generalized‐gradient approximation (GGA) to calculate the electronic and optical properties of SnS. Optical properties were computed using independent particle approximation (IPA) and BSE with DFT+U wave functions. Our theoretical results align with experimental data for this material, demonstrating the potential for further research in validating experimental results with theoretical approximations and empirical relations. [ABSTRACT FROM AUTHOR]

We examine the electronic, optical, and dielectric properties of Cu-, Ag-, and Au-doped and undoped cadmium hydroxide [Cd(OH)2)] using first-principles density functional theory. The electronic investigations show the semiconducting characteristics of Cd(OH)2 with a band gap of about 1.83 eV. These properties were investigated along two mutually perpendicular directions of light polarization and as a function of the incident light energy (photon energy). The frequency-dependent dielectric function is obtained from the electronic structure calculations. The optical quantities, such as absorption, transmission, refractive index, etc., are also calculated to investigate the optical behavior. The metal doping (Cu, Ag, and Au) significantly affects the properties of Cd(OH)2 in the infrared and low-energy visible regions of the electromagnetic spectrum. For photon energies greater than 4.0 eV, the effect of these doping elements on the optical and dielectric properties is negligible. These materials exhibit negative dielectric permittivity, which is one of the fundamental features of a photonic crystal. The low-energy absorption spectrum of the doped material shows a shift towards the longer wavelengths compared to the undoped Cd(OH)2. This shift is maximum (minimum) for Cu (Au)-doped Cd(OH)2, whereas Ag-doped Cd(OH)2 has an intermediate shift compared to Cu- and Au-doped Cd(OH)2. This relative shift may be attributed to their atomic radii. These are good candidates for the absorption of UV radiation. The calculated static refractive index of Ag-doped Cd(OH)2 is comparable to SiO2. These electronic and optical investigations reveal that the considered materials are excellent candidates for optoelectronic device applications. [ABSTRACT FROM AUTHOR]

We investigate the pressure effect on Li4OX2 (X = Cl, Br, and I) for the first time using DFT simulation. Li4OCl2 shows mechanical stability up to 8 GPa, whereas Li4OBr2 has stability up to 30 GPa pressure according to the Born stability criteria. In contrast, Li4Ol2 becomes unstable above 3.0 GPa pressure. Hence, anomalies were observed for Li4OX2 (X = Cl, Br, and I) solid electrolyte for elastic parameters, Cij under pressure study. The elastic moduli are isotropic in the xy plane, conversely, along the xz and yz plane anisotropic behavior is observed. There is a band gap that exists at zero temperature and pressure. The contribution at the fermi level mainly comes from the O 2p states. The highest reflectivity (∼98 %) was observed for Li4OCl2 at ∼ 17 eV in the IR-visible-UV region showing that this material under study may be considered as a potential coating material to avoid solar heating. The smaller value of the volume thermal expansion coefficient for Li4OCl2 indicates stronger atomic bonding exists, which was also observed from the elastic parameter analysis.

Researchers are working on perovskites for photovoltaic applications due to their low cost and excellent power conversion efficiency. Our investigation has focused on analyzing the effects of hydrostatic strain on the structural, electronic, optical and thermoelectric properties of CsSnBr3. The calculated structural properties and enthalpy of formation imply that these structures are stable under different strain conditions. Our investigation shows that the CsSnBr3 compound is a direct semiconductor with an electronic band gap of 1.272 eV, which can be tuned from 0.604 eV to 1.823 eV under different strain conditions. As the compressive strain increases, the light absorption spectrum of CsSnBr3 undergoes a red shift, causing a prolongation of the light absorption edge. The thermoelectric properties show that CsSnBr3 is a p-type semiconductor. Our findings indicate that the CsSnBr3 material is highly suitable for photovoltaic applications. [ABSTRACT FROM AUTHOR]

Natural dye sensitizers are substances that are sensitive to light colour and can be classified into several classes based on their chemical structure. Theaflavin pigments are unexplored natural dyes used as light sensitizers derived from black tea waste. However, the efficiency of natural dye-sensitized solar cells (DSSC) is lower than that of synthetic ones. To increase the efficiency, an amine donor molecule, a thiophene bridge, and a cyanoacrylic acid anchoring group were added. This improvement was achieved by comparing the LHE values, absorption shifts towards the red spectrum, and electronic parameters before and after modification of the theaflavin structure. This study aimed to analyze the effect of a fused thiophene bridge on the colour pigment of theaflavin on the electronic and optical properties of DSSC. TDDFT was employed with the hybrid functional B3LYP and def2-SVP. The calculated results concluded that adding fused thiophene can shift the wavelength with a maximum value of 256 nm and an increase in LHE of 40%. The addition of five thiophenes can shift the absorption wavelength closer to the red spectrum and satisfy the electronic properties of the DSSC, and the number of electron donor and acceptor sites obeying the law of conservation of charge. [ABSTRACT FROM AUTHOR]

As layered materials, transition metal dichalcogenides (TMDCs) are promising two-dimensional (2D) materials. Interestingly, the characteristics of these materials are transformed from bulk to monolayer. The atomically thin TMDC materials can be a good alternative to group III–V and graphene because of their emerging tunable electrical, optical, and magnetic properties. Although 2D monolayers from natural TMDC materials exhibit the purest form, they have intrinsic defects that limit their application. However, the synthesis of TMDC materials using the existing fabrication tools and techniques is also not immune to defects. Additionally, it is difficult to synthesize wafer-scale TMDC materials for a multitude of factors influencing grain growth mechanisms. While defect engineering techniques may reduce the percentage of defects, the available methods have constraints for healing defects at the desired level. Thus, this holistic review of 2D TMDC materials encapsulates the fundamental structure of TMDC materials, including different types of defects, named zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D). Moreover, the existing defect engineering methods that relate to both formation of and reduction in defects have been discussed. Finally, an attempt has been made to correlate the impact of defects and the properties of these TMDC materials. [ABSTRACT FROM AUTHOR]

Recent huge progress in the field of chemical doping for modifying the physical properties of nano-materials has inspired us to perform this investigation on the electronic and optical properties of GeSe/SnSe vertical heterojunction via P-doping. The calculated results indicate that the pristine GeSe/SnSe vertical heterojunction is a semiconductor and shows a type-II band alignment. After P-doping, all doped heterojunctions have good structural stability due to the negative binding energies. Interestingly, the typical p-type and n-type degenerate semiconductors can be found. In addition, the optical properties including the absorption coefficient, reflectivity and loss function of P-doped GeSe/SnSe vertical heterojunction are discussed. Particularly, in the ultraviolet light range, the optical absorption coefficient of P-doped systems can reach up to 1 4 × 1 0 5 cm − 1 , which suggests that P-doping GeSe/SnSe vertical heterojunctions can serve as a promising material for ultraviolet light detecting. Meanwhile, the absorption and the loss peaks of doped cases exhibit an apparent trend of blue shift with respect to the pristine heterojunction. All these interesting results show that the P-doping gives GeSe/SnSe heterojunction the possibility to tune its electronic and optical properties. [ABSTRACT FROM AUTHOR]

The electronic, optical, and anticorrosion properties of planer ZnO crystal and quantum dots are explored using density functional theory calculations. The calculations for the finite ZnO quantum dots were performed in Gaussian 16 using the B3LYP/6-31g level of theory. The periodic calculations were carried out using VASP with the plane wave basis set and the PBE functional. The subsequent band structure calculations were performed using the hybrid B3LYP functional that shows accurate results and is also consistent with the finite calculations. The considered ZnO nanodots have planer hexagonal shapes with zigzag and armchair terminations. The binding energy calculations show that both structures are stable with negligible deformation at the edges. The ZnO nanodots are semiconductors with a moderate energy gap that decreases when increasing the size, making them potential materials for anticorrosion applications. The values of the electronic energy gaps of ZnO nanodots are confirmed by their UV-Vis spectra, with a wide optical energy gap for the small structures. Additionally, the calculated positive fraction of transferred electrons implies that electron transfer occurs from the inhibitor (ZnO) to the metal surface to passivate their vacant d-orbitals, and eventually prevent corrosion. The best anti-corrosion performance was observed in the periodic ZnO crystal with a suitable energy gap, electronegativity, and fraction of electron transfer. The effects of size and periodicity on the electronic and anticorrosion properties are also here investigated. The findings show that the anticorrosion properties were significantly enhanced by increasing the size of the quantum dot. Periodic ZnO crystals with an appropriate energy gap, electronegativity, and fraction of electron transfer exhibited the optimum anticorrosion performance. Thus, the preferable energy gap in addition to the most promising anticorrosion parameters imply that the monolayer ZnO is a potential candidate for coating and corrosion inhibitors. [ABSTRACT FROM AUTHOR]

First-principles calculations have been performed on (HfO 2) p and Hf q Zr r O 2 (q + r) clusters using DFT and TDDFT. The effect of Zr-substitution on the structural, electronic, thermodynamic, and optical properties of (HfO 2) p clusters has been investigated using B3LYP and B3PW91 functionals with LANL2DZ basis set. The calculated properties depend upon geometry, type, and number of atoms present in the clusters. Zr-substitution in (HfO 2) p clusters leads to the reduced molecular mass of Hf q Zr r O 2 (q + r) clusters so that they can be used in making light weight semiconductor devices. Hf 3 Zr 2 O 10 is found to be the most reactive after Zr-substitution in (HfO 2) 5 because of the minimum value of HOMO-LUMO gap. Zr-substitution in (HfO 2) 5 increases the refractive index of Hf 3 Zr 2 O 10 , making it suitable for multi-layer antireflecting coatings. The dielectric constant of Hf 3 Zr 2 O 10 has increased after Zr-substitution finding applications in the MOSFET industry. The absorption spectra can be tuned over the ultraviolet and visible regions depending upon the Zr-substitution. [ABSTRACT FROM AUTHOR]

Perovskite solar cells are the future of energy production due to the high- efficiency and low production costs. In this work, the structural, electronic and optical properties of the tetragonal inorganic halideperovskiteRbSeBr3 are performed using the full potential linearized augmented plane waves (FP-LAPW) method with the PerdewBurke–Ernzerh generalized gradient approximation (PBE-GGA) as well as the local density approximation (LDA) and the modified Becke-Johnson (mBJ-LDA) as exchange correlation potentials using Wien2k code. Furthermore, the thermoelectric propertieshave been calculated using BoltzTrap code, the obtained results show that the studied compound (RbSeBr3) has a metallic character and can be used as an absorber in UV-interval; on the other hand the thermoelectric power reveals a high value.

New nanobelts and nanoribbons are built from zigzag-hexagonal graphene quantum dots. Their stability, electronic, optical, and sensing properties are studied using density functional theory calculations. The infrared spectra's real vibrational frequencies and positive binding energy prove the stability of the constructed structures. The thermal stability at 600 K is also confirmed by molecular dynamics simulations. The nanobelts have a significantly low energy gap compared to the planer single quantum dots or the extended nanoribbons based on these nanodots. This is a result of the wrapping of the graphene nanodots which raises the π-overlapping between adjacent rings that decreases the energy gap. Interactive electronic states localized at the zigzag edges characterize both nanobelts and nanoribbons. Thus these systems are promising candidates for sensing and catalytic applications. Their sensing capability is tested by studying the adsorption of selected volatile organic compounds such as chloromethane and trichloroethylene. The findings indicate that these gases are effectively adsorbed with moderate adsorption energy and charge transfer, opening the door toward gas sensor applications.

The electronic and optical properties and hydrogen storage capacity of doped two-dimensional TiO2 quantum dots are studied using density functional theory computations. The considered dopants are C, S, N, Fe, Ni, and Zn. Temperature stability is confirmed at 500 K according to ab initio molecular dynamics simulations. Doping and vacancy formation increase the energy gap due to the relaxation of Ti-atoms by additional electrons from the dopants or surface reconstruction after removing O or Ti atoms. The UV–Vis absorption spectra imply that the dominant absorption peak experiences a blue shift after doping and vacancies. The pristine TiO2 is promising for hydrogen storage with suitable adsorption energy that can be enhanced by doping. We obtained a gravimetric adsorption capacity of 6.23 wt% which is higher than the 6.0 wt% issued by the US Department of Energy. Therefore, the high adsorption capacity/energy and thermal stability render TiO2 nanodots promising for efficient H2-storage devices.

Herein, the biaxial strain effect is investigated on the structural, electronic, and optical properties of 1T and 1H phases of Janus CaFBr monolayer in the framework of density functional theory. It is found that both phases of the Janus CaFBr monolayer are direct semiconductors at equilibrium, with bandgaps of 3.90 and 3.55 eV for 1T and 1H phases, respectively. The thermodynamic stability is examined via cohesive energy and phonon dispersion. The bandgap decreases linearly and is nearly parabolic for 1T and 1H phases, respectively, when switching from the tensile to compressive strain with a drastic shift from direct to indirect bandgap at −10% of compressive strains. The calculated dielectric function and optical properties such as reflectivity, refractive index, extinction, and absorption coefficients enhance under biaxial with an improvement of the absorption coefficient especially in the visible and ultraviolet (UV) regions for 1H and 1T phases, respectively, which is in line with the dielectric constant. The results suggest that the Janus CaFBr monolayer might be a potential candidate for optoelectronic applications in visible/UV detection and absorption. [ABSTRACT FROM AUTHOR]

Context: Heavy metals are highly noxious, and their presence can cause diverse effects on living organisms and the environment. Crown ether porphyrins and phthalocyanines are known to effectively extract these pollutants and are also used in photovoltaic devices. This study aims to evaluate various factors that govern intramolecular charge transfer (ICT) and photo-injection processes, including maximum absorption wavelength (λmax), density of states (DOS), charge transfer dipole (μCT), light harvesting efficiency (LHE), open-circuit voltage (Voc), and free energy change of electron injection (ΔGinj) in order to investigate the performance of different compounds designed from metalloporphyrins for bulk-heterojunction organic solar cell (BHJ-OSC) applications. The porphyrin complex showed the best optoelectronic properties, with remarkable LHE values and CT amounts compared to phthalocyanine derivatives. The central metal played a significant role in optimizing the optical properties of the materials for use in solar cells. HgPr4O and CdPr4O were found to have optimal Voc values, resulting in effective injection, high electron, and hole mobilities, making them ideal materials for highly efficient BHJ-OSC devices. Methods: Density functional theory (DFT) approach was employed with the B3LYP functional and the def2TZVP basis set as implemented in the Gaussian 16 revision C.01 program to investigate the designed complexes and to compute geometrical parameters, frontier molecular orbitals (FMOs), and natural bond orbital (NBO). Furthermore, the time-dependent density functional theory (TD-DFT) method was used to analyze the optical properties and photovoltaic characteristics of selected metalloporphyrins by examining the UV-Vis spectra. In summary, the study presents a thorough description of the structural and electronic properties of the investigated complexes and provides insights into their potential use in photovoltaic applications. [ABSTRACT FROM AUTHOR]

We have studied the effects of uniaxial strain on the electronic and optical properties in CsPbI3 perovskite using density functional theory. The unstrained CsPbI3 has a band gap energy of 1.63 eV. We have applied a compressive and tensile strain (− 5% to 5%) in each of the three crystallographic directions independently. We have observed an anisotropic behavior in the variation of the band gap energy in the case of a tensile strain along the c-direction, where the band gap varies differently compared to the case of a tensile strain along the a- and b-directions. This unusual behavior appears up to a tensile strain of 3.5%, where the band gap energy reaches a value of 1.74 eV. The key factor of this atypical behavior was attributed to the distortion of the structure caused by the inclination of the PbI6 octahedral, the deviation of the Pb-I-Pb angle from the ideal angle of 180°. Furthermore, through ab initio calculations, we found that CsPbI3 has several interesting optical properties related to the strain, remarkable optical absorption (about 105 cm−1), refractive index (2.25) and excellent optical conductivity. These properties make CsPbI3 a very promising candidate for Optoelectronics applications. [ABSTRACT FROM AUTHOR]

Black and blue SiSe monolayers are new types of group IV–VI two-dimensional semiconductors. The structural, electrical, and optical characteristics of black and blue SiSe monolayers subjected to in-plane biaxial strain are examined using first-principles calculations. Both monolayers exhibit an indirect band gap that is sensitively dependent to the application of strain. The black and blue SiSe monolayers have band gaps of 1.11 eV (2.94 eV) and 0.62 eV (2.12 eV) computed by the Perdew–Burke–Ernzerhof (PBE) Heyd–Scuseria–Ernzerhof (HSE06) functional. The band gap (based on HSE06 method) reduces when compressive or tensile biaxial strain is applied to the blue SiSe monolayer. The electronic band gap of the black SiSe monolayer increases with the tensile biaxial strain and reduces in the presence of compressive biaxial strain. We found that the blue SiSe monolayer remains a semiconductor under biaxial strain from −6% to 6%, while the black SiSe monolayer experiences a transition from semiconductor to metal when subjected to compressive biaxial strain of about −4%. These results show very intriguing possibilities to modify the electrical and optical properties of SiSe sheet. [ABSTRACT FROM AUTHOR]

The electronic and optical properties of finite GaS nanoribbons are investigated using density functional theory calculations. The effect of size, edge termination, and chemical modification by doping and edge passivation are taken into account. The dynamical stability is confirmed by the positive vibration frequency from infrared spectra; further, the positive binding energies ensure the stable formation of the considered nanoribbons. Accurate control of the energy gap has been achieved. For instance, in armchair nanoribbons, energy gaps ranging from ~ 1 to 4 eV were obtained in varying sizes. Moreover, the energy gap can be increased by up to 5.98 eV through edge passivation with F-atoms or decreased to 0.98 eV through doping with Si-atoms. The density of states shows that the occupied molecular orbitals are dominated by S-atoms orbitals, while unoccupied ones are mostly contributed to by Ga orbitals. Thus, S-atoms will be the electron donor sites, and Ga-atoms will be the electron acceptors in the interactions that the nanoribbons might undergo. The nature of electron–hole interactions in the excited states was investigated using various indices, such as electron–hole overlapping, charge–transfer length, and hole–electron Coulomb attraction energy. The UV-Vis absorption spectra reveal a redshift by increasing the size in the armchair or the zigzag directions. Chemical functionalization shows a significant influence on the absorption spectra, where a redshift or blueshift can be achieved depending on the dopant or the attached element. [ABSTRACT FROM AUTHOR]

This work systematically studies the electronic and optical properties of H-terminated armchair silicene nanoribbon (HASiNR) for oxygen (O2) adsorption using first-principles calculations. The results show that the most stable site for O2 adsorption is the edge of the ribbon, which possesses relatively low adsorption energy of −2.46 eV, indicating good stability. Particularly, the adsorption energy decreases gradually with the increase of the oxygen concentration. It was also found that the direct bandgap of HASiNR can be effectively tuned by changing the adsorption concentration of O2 gas. Additionally, the analysis of the density of states shows that the adsorption of O2 on HASiNR is chemisorption due to the apparent charge transfer from the ribbon to O2 gas. Besides, the work function, absorption coefficient and refractive index of the HASiNR are sensitive to O2 gas adsorption. Therefore, our studies prove that oxygen gas adsorption allows the HASiNR to modulate its electronic and optical properties. [ABSTRACT FROM AUTHOR]

A series of hexagonal group IV-V (IV=C, Si, Ge, V=N, P, As) phase-α and -β monolayers are studied using the first-principle calculation. The 18 monolayers are all optical transparent semiconductors with band gaps in the range of 1.91–6.06 eV and have good light adsorption in UV range. And each monolayer has its own unique properties. The CN phase-α and -β monolayers have good mechanical properties (large 2D Young's moduli, 555.3 N m−1 and 585.5 N m−1) comparable to that of two layer graphene. The CP-β monolayer is the only one with direct band gap and can translate into indirect semiconductor when applied biaxial tensile strain greater than 4 %, while the CP-α, CAs-α and CAs-β monolayers can realize the transition from the indirect semiconductor to direct one with 6–10 % biaxial tensile strain. The SiN and GeN monolayers are ductile with large Poisson's ratio (∼0.30). And the GeN monolayers can maintain indirect band gaps under 10 % strain and have linear relationships between the band gaps and strains. The GeAs monolayers have partial light adsorption in visible range (several 104 cm−1 in 390–450 nm) and possess water-splitting photocatalytic properties under suitable conditions (neutral and alkaline for the GeAS-α and alkaline for GeAS-β). The different properties of each hexagonal group IV-V (IV=C, Si, Ge, V=N, P, As) binary monolayers can be potential applied in different two dimensional electronic devices. [ABSTRACT FROM AUTHOR]

The electronic, optical, and anticorrosion properties of planer ZnO crystal and quantum dots are explored using density functional theory calculations. The calculations for the finite ZnO quantum dots were performed in Gaussian 16 using the B3LYP/6-31g level of theory. The periodic calculations were carried out using VASP with the plane wave basis set and the PBE functional. The subsequent band structure calculations were performed using the hybrid B3LYP functional that shows accurate results and is also consistent with the finite calculations. The considered ZnO nanodots have planer hexagonal shapes with zigzag and armchair terminations. The binding energy calculations show that both structures are stable with negligible deformation at the edges. The ZnO nanodots are semiconductors with a moderate energy gap that decreases when increasing the size, making them potential materials for anticorrosion applications. The values of the electronic energy gaps of ZnO nanodots are confirmed by their UV-Vis spectra, with a wide optical energy gap for the small structures. Additionally, the calculated positive fraction of transferred electrons implies that electron transfer occurs from the inhibitor (ZnO) to the metal surface to passivate their vacant d-orbitals, and eventually prevent corrosion. The best anti-corrosion performance was observed in the periodic ZnO crystal with a suitable energy gap, electronegativity, and fraction of electron transfer. The effects of size and periodicity on the electronic and anticorrosion properties are also here investigated. The findings show that the anticorrosion properties were significantly enhanced by increasing the size of the quantum dot. Periodic ZnO crystals with an appropriate energy gap, electronegativity, and fraction of electron transfer exhibited the optimum anticorrosion performance. Thus, the preferable energy gap in addition to the most promising anticorrosion parameters imply that the monolayer ZnO is a potential candidate for coating and corrosion inhibitors.

We conducted a systematic investigation using state-of-the-art techniques on the electronic and optical properties of two crystals of alkaline earth metal fluorides, namely rutile MgF 2 and cubic SrF 2 . For these two crystals of different symmetry, we present density functional theory (DFT), many-body perturbation theory (MBPT), and Bethe–Salpeter equation (BSE) calculations. We calculated a variety of properties, namely ground-state energies, band-energy gaps, and optical absorption spectra with the inclusion of excitonic effects. The quantities were obtained with a high degree of convergence regarding all bulk electronic and optical properties. Bulk rutile MgF 2 has distinguished ground-state and excited-state properties with respect to the other cubic fluoride SrF 2 and the other members of the alkaline earth metal fluoride family. The nature of the fundamental gaps and estimates of the self-energy and excitonic effects for the two compounds are presented and discussed in detail. Our results are in good accordance with the measurements and other theoretical–computational data. A comparison is made between the excitation and optical properties of bulk rutile MgF 2 , cubic SrF 2 , and the corresponding clusters, for which calculations have recently been published, confirming strong excitonic effects in finite-sized systems. [ABSTRACT FROM AUTHOR]

The van der Waals (vdWs) heterostructure retains some excellent properties of monolayer transition metal dichalcogenides (TMDs), and has a significant improvement in performance, which is anticipated to play an important role in optoelectronic devices. S vacancy and interlayer interaction act together to influence the properties of the system. In this work, based on first-principles calculations, the effect of S vacancy on the electronic and optical properties of the MoS2/WSe2 heterostructure were investigated. The calculation demonstrated that a single S vacancy introduces defect states between the conduction band minimum (CBM) and the Fermi level. For optical properties, the formed, built-in electric field of a heterostructure would prevent electron and hole recombination. Both systems show strong light absorption in the visible and ultraviolet regions. The absorption coefficient in the infrared regions of the defected MoS2/WSe2 heterostructure was larger than that of the perfect heterostructure. The defect states were influenced by interlayer distance. The defected MoS2/WSe2 heterostructure experienced a direct-gap semiconductor to metal, and the band gap decreased with decreasing layer distance. Also, all the systems showed strong light absorption in the visible and ultraviolet regions. As for the near-infrared region, light absorption of the defected MoS2/WSe2 heterostructure was more obvious as the interlayer distance decreased, while the smaller the layer distance, the more obvious was the absorption in the near-infrared region. In summary, S vacancy and interlayer interaction have important effects on the electronic structure and optical properties of the MoS2/WSe2 heterostructure, which is helpful for the design of multifunctional high-performance optoelectronic devices. [ABSTRACT FROM AUTHOR]

In this work, the electronic and optical properties of the A l 0.75 V 0.25 N compound in the rock-salt structure are investigated using the first-principles calculations based on spin density functional theory within the ultrasoft pseudopotential method. The exchange-correlation potential was treated with the G G A - P B E and G G A + U PBESol approaches where the Hubbard-U term has been employed to better describe the electronic and optical properties of the strongly correlated system A l 0.75 V 0.25 N . The negative formation energy found and phonon dispersion calculations show that the A l 0.75 V 0.25 N compound is both dynamically and thermodynamically stable in the ground state. This ternary alloy is predicted with GGA to be ferromagnetic metal in nature with a magnetic moment of 1.62 μ B and ferromagnetic semiconductor when including Hubbard-U corrections ( G G A + U ) with a magnetic moment of 2 μ B , so it is a diluted magnetic semiconductor. In addition, several optical properties such as dielectric function, absorption, and reflectivity have been analyzed. Obtained results suggest that A l 0.75 V 0.25 N is a potential candidate for the spintronic and applications in optoelectronic devices. [ABSTRACT FROM AUTHOR]

The effects of temperature and electric field on the electronic and optical properties of spherical InAs quantum dot (QD) at the center of n-type cylindrical nanowire are investigated in this theoretical study. By solving the Schrodinger-Poisson equation self-consistently, the energy levels, band structure and electrostatic potential of the structure are calculated. The numerical results show that the temperature variations have a great influence on the electronic and optical properties. The results show that the strength of energy eigenvalues bounded in the quantum dot region, the depletion region on either side of the dot, carrier charges densities and transition energy ( depend on temperature. Furthermore, as the temperature rises, the blue shifts in absorption peaks and changes in refractive, as well as their amplitude are observed. Concomitantly the ground state-first excited state intraband transition energy increases when the applied electric field is enhanced, while the electric dipole matrix elements are diminished. The results of this research could be useful in designing the quantum dot optoelectronic devices. [ABSTRACT FROM AUTHOR]

The electronic and optical properties of finite GaS nanoribbons are investigated using density functional theory calculations. The effect of size, edge termination, and chemical modification by doping and edge passivation are taken into account. The dynamical stability is confirmed by the positive vibration frequency from infrared spectra; further, the positive binding energies ensure the stable formation of the considered nanoribbons. Accurate control of the energy gap has been achieved. For instance, in armchair nanoribbons, energy gaps ranging from ~ 1 to 4 eV were obtained in varying sizes. Moreover, the energy gap can be increased by up to 5.98 eV through edge passivation with F-atoms or decreased to 0.98 eV through doping with Si-atoms. The density of states shows that the occupied molecular orbitals are dominated by S-atoms orbitals, while unoccupied ones are mostly contributed to by Ga orbitals. Thus, S-atoms will be the electron donor sites, and Ga-atoms will be the electron acceptors in the interactions that the nanoribbons might undergo. The nature of electron–hole interactions in the excited states was investigated using various indices, such as electron–hole overlapping, charge–transfer length, and hole–electron Coulomb attraction energy. The UV-Vis absorption spectra reveal a redshift by increasing the size in the armchair or the zigzag directions. Chemical functionalization shows a significant influence on the absorption spectra, where a redshift or blueshift can be achieved depending on the dopant or the attached element.

In the field of material science, the search for a material with an optimal bandgap of approximately 1.40 eV that can act as an efficient photocatalyst for water splitting using solar spectrum irradiation is a noble mission. In this article, we explore the structural, electronic structure, optical and photocatalytic properties of Zr 2 CO 2 /MoS 2 vdW heterostructures. Our results demonstrates that the Zr 2 CO 2 /MoS 2 vdW heterostructure can be reliably synthesized. This is due to a minimal lattice mismatch of less than 3%, a negative adhesion energy of -4.23 meV/Å 2 , and inherent dynamic stability. The electronic band structure calculations indicate that the Zr 2 CO 2 /MoS 2 vdW heterostructure is an indirect bandgap semiconductor. We found that the conduction band minimum (CBM) and valance band maximum (VBM) of the heterostructure are located in different monolayers. Furthermore, under − 2 % biaxial strain a transition from type-I to type-II (staggered) band alignment occurred. Stacking 2D MoS 2 on the Zr 2 CO 2 monolayer results in a vdW heterostructure, and as a result, the HSE calculated bandgap of the Zr 2 CO 2 /MoS 2 vdW heterostructure in most stable configuration lying in the ideal range for photocatalytic applications. We also studied the heterostructure's optical properties to understand its response to incident photons with energies up to 14 eV. Based on our findings, Zr 2 CO 2 /MoS 2 heterostructures are desirable for optoelectronic device applications operated in visible range. Our research offers fresh recommendations for developing novel, highly effective photocatalytic compounds with numerous optical device applications. [ABSTRACT FROM AUTHOR]

We present an extensive analysis of the structural, electronic, optical, elastic, and thermoelectric properties of B i G a 2 X 4 compounds, where X represents either sulfur (S) or selenium (Se). Our approach employed the all-electron full potential linearized augmented plane wave (FP-LAPW) technique, offering a comprehensive understanding of these materials' characteristics. The calculated lattice constants (a), the unit cell height (c), and the c/a ratio closely match experimental data, affirming the accuracy of our calculations. A pivotal focus of our study was on the electronic properties, including the indirect bandgaps (A → M − Γ) and (M → A). We found that Bi Ga 2 S 4 exhibited an indirect bandgap (E g) of 2.504 eV, while Bi Ga 2 Se 4 possessed a slightly lower value of 1.878 eV. This variation was primarily attributed to the intricate interactions among bismuth, sulfur, and selenium atoms, particularly involving p − p orbital interactions. Additionally, we explored the optical characteristics of these compounds, determining their maximum absorption wavelengths. B i G a 2 S 4 exhibited an absorption peak at 4.476 eV, whereas B i G a 2 S e 4 displayed a slightly lower maximum absorption at 3.741 eV. Moreover, B i G a 2 S e 4 showcases a higher dielectric constant, which augments its potential for optoelectronic applications. A critical aspect of our research is the assessment of the elastic properties, elucidating that both compounds exhibited fragility and anisotropy. We observed that at 300 K, the lattice thermal conductivity (k L) for B i G a 2 S 4 and B i G a 2 S e 4 was measured at 1.57 W / mK and 1.14 W / mK , respectively, indicating low thermal conductivity. At 1000 K, both BiGa 2 S 4 , and BiGa 2 Se 4 exhibit significant ZT values of 0.8389 and 0.8722, respectively. The ZT values of the p -type semiconductors are notably higher than those of the n -type. At T = 900 K, the optimized ZT values for BiGa 2 S 4 , and BiGa 2 Se 4 are found to be 0.82909 and 0.90548, respectively. Achieving these values requires either increasing the concentration of charge carriers to n = 0.11715 x 1022 cm−3 for BiGa 2 S 4 and n = 0.0812 x 1022 cm−3 for BiGa 2 Se 4 , or reducing the chemical potentials by 0.40151 Ryd and 0.38001 Ryd, respectively. • B i G a 2 S 4 has an indirect bandgap of 2.504 eV, while B i G a 2 S e 4 has a slightly lower value of 1.878 eV due to p-p orbital interactions. • B i G a 2 S 4 Shows an absorption peak at 4.476 eV; B i G a 2 S e 4 displays a lower maximum absorption at 3.741 eV with higher dielectric constant. • At 1000 K, B i G a 2 S 4 and B i G a 2 S e 4 exhibit significant ZT values of 0.8389 and 0.8722, respectively, indicating good thermoelectric performance. [ABSTRACT FROM AUTHOR]

A series of indole (In) and carbazole (Cz) derivative monomers have been synthesized, such as 4-[3-carbazolyl] indole (4In-3Cz), 5-[3-carbazolyl] indole (5In-3Cz), 6-[3-carbazolyl] indole (6In-3Cz), 7-[3-carbazolyl] indole (7In-3Cz). The comonomers synthesized by Stille coupling reaction were characterized by 1 H-NMR and elemental analysis. Potentiodynamic method was used for electropolymerization of comonomers, Indole, Cz, and the mixture of In and Cz. Electrochemical activities of resulting P[4In-3Cz], P[5In-3Cz], P[6In-3Cz], P[7In-3Cz], polyindole (PIn), polycarbazole (PCz) and P[In-co-Cz] films were investigated comparatively by CV at different scan rates, electrochemical impedance spectroscopy (EIS) and spectroelectrochemical measurements. The ionization potentials, Ip, specific capacitance, Csp, and optical band gap, Eg, of copolymers were obtained from these measurements. In order to gain some preliminary information on the structure of the copolymers, DFT analysis was performed and dimers and tetramers were optimized. Results suggested that, in order to obtain an In-Cz copolymer with low oxidation potential and band gap, indole ring should be substituted through 5 position to the 3 position of Cz. If high specific capacitance value or high conductivity are desired, P[4In-3Cz] and P[6In-3Cz] are the best copolymers, respectively. [ABSTRACT FROM AUTHOR]

Dimensionality is the game-changer property of a material. The optical and electronic properties of a compound get dramatically influenced by confining dimensions from 3D to 2D. The bulk 3D perovskite materials have shown remarkable up-gradation in the power conversion efficiency, hence grabbing worldwide attention. But instability against moisture, temperature, and ion migration are the factors constantly back-stabbing and hindering from full-scale commercialization. 2D perovskite material has emerged as an excellent bridging entity between structural-chemical stability, and viable commercialization. Organicâ€"inorganic 2D perovskite materials come with a layered structure in which a large organic cation layer as a spacer is sandwiched between two inorganic metal halide octahedra layers. Moreover, hydrophobic spacer cations are employed which isolate inorganic octahedral layers from water molecules. Hydrophobic spacer cations protect the authentic structure from being degraded. These layered structures occur in two phases namely the Ruddlesdenâ€"Popper phase and Dionâ€"Jacobson phase, depending on the spacer cation types. Alternating inorganic and organic layers form multiple quantum wells naturally, along with spinâ€"orbit-coupling gives Rashba splitting. 2D perovskite materials are coming up with interesting chemical, physical properties like exciton dynamics, charge carrier transport, and electronâ€"phonon coupling as a result of the quantum confinement effect. Despite appreciable stability, limited charge transport and large bandgap are limiting the application of 2D perovskite materials in solar cells. These limitations can be overcome by using the concept of 2D/3D multidimensional hybrid perovskites, which includes the long-term stability of 2D perovskite and the high performance of 3D perovskite at the same time. Here in this perspective, we have given brief insight on structural versatility, synthesis techniques, some of the unique photophysical properties, potential device fabrication, and recent advancements in the 2D structure to stand against degradation. Certain shortcomings and future outlooks are also discussed to make the perspective more informative. [ABSTRACT FROM AUTHOR]

The emergence of hybrid organic–inorganic perovskites (HOIPs) has made great progress in the photovoltaic (PV) field. In recent years, more and more articles have shown that the modification of organic cations can improve HOIPs’ performance, and a surge of interest has been paid to rethink the effect of organic cations. In our review, we summarized the influences of organic cation rotation on structure, optoelectrical properties, and stability. We also provide theoretical insights into why and how organic cations affect the performance of HOIPs in experiments. At last, we have proposed possible control methods and development directions in the hope that the rotation of organic cation can be better observed and utilized in inherently tunable perovskite materials, solar cells, LED, photocatalysis, photothermal conversion, and other related fields.

By utilizing the tight-binding method, the electronic spectrum and states distribution of square Janus monolayer black arsenic phosphorus (b-AsP) quantum dots (QDs) in the presence of a perpendicular magnetic field are explored. Strong in-gap states of b-AsP QDs, whose probability densities are distributed on the armchair boundary (armchair edge states) appear in the energy gap of host perfect two-dimensional b-AsP. The corresponding energy levels of the armchair edge states can degenerate to the Landu energy levels upon applying a perpendicular magnetic field. When an in-plane polarized light is introduced, due to the presence of armchair edge states, the edge-to-edge transitions are mainly induced from the armchair edge (hole) states to zigzag edge (electron) states. The optical absorption undergoes blue shift as a function of the magnetic field. Our work suggests tunable optical properties via modulating the armchair edge states of a b-AsP QD and provides a theoretical basis for the design of b-AsP-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

Derived from an excellent light harvester, an iminodibenzyl-substituted porphyrin sensitizer consisting of a series of D-π-A-A structural motifs, was investigated using density functional theory (DFT) and time-dependent DFT methods to demonstrate the effects of various auxiliary acceptors on sensitizers. Absorption spectra simulations at 417.51 nm calculated using CAM-B3LYP with a mixed LanL2DZ/6-31G(d,p) basis set exhibited good agreement with the experimental results (i.e., 426.60 nm). Impressively, the introduction of a co-acceptor moiety on the sensitizers effectively shifted the light absorption to the NIR region. The computational results showed that Dye 9 notably exhibited the smallest HOMO–LUMO energy gap (3.34 eV). The Q band of Dye 9 was located at 756.72 nm, which was the largest wavelength and the most redshifted absorption spectrum. The short-circuit current density ( J SC ) was calculated by considering the free energy of charge injection ( Δ G inject ), the free energy of dye regeneration ( Δ G reg ), and light-harvesting efficiency (LHE). The oscillator strength of the maximum absorption was greatest for Dyes 3 and Dye 9, resulting in increase LHE and improved J SC , hence affecting the overall photoelectric conversion efficiency. Dye 9 demonstrated better electron transfer performance, with q CT (0.630 e−), which was attributed to its better planarity compared to other dyes. Interestingly, Dye 9 exhibited substantially enhanced nonlinear optical response through intramolecular charge transfer process, with a β tot value many-fold higher than that of urea computed at the same theoretical level. It indicates that the studied dye molecules are potential candidates for the optoelectronic applications. Dye 9 was therefore the most feasible dye candidate for efficient DSSC applications. [ABSTRACT FROM AUTHOR]

The configurations of nine different non-metals doped silicon carbide (NM-SiC) were structured by using the density functional theory (DFT). The magnetic, electronic, and optical properties of each NM-SiC are investigated at the most stable structure with the maximum binding energy. Although the O-, Si-, and S-SiC systems are still non-magnetic semiconductors, the N- and P-SiC systems have the properties of the magnetic semiconductors. The H-, F-, and Cl-SiC systems exhibit the half-metal behaviors, while the B-SiC system converts to magnetic metal. The redistribution of charges occurs between non-metals atoms and adjacent C atoms. For the same doping position, the more charges are transferred, the greater the binding energy of the NM-SiC system. The work function of the NM-SiC systems is also adjusted by the doping of NM atoms, and achieves the minimum 3.70 eV in the P-SiC, just 77.1% of the original SiC. The absorption spectrum of the NM-SiC systems occurs red-shift in the ultraviolet light region, accompanying the decrease of absorption coefficient. These adjustable magnetic, electronic, and optical performances of NM-SiC expand the application fields of two-dimensional (2D) SiC, especially in designing field emission and spintronics devices.