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The electronic properties of hexagonal and d-NaCl structure of monolayer GeTe, as well as the effect of external biaxial strain and electric field, were studied by first-principles calculations. The calculated binding energy theoretically indicated a slightly greater possibility of forming two-dimensional (2D) GeTe with a d-NaCl structure. The band structures of d-NaCl monolayer GeTe were dramatically transformed from semiconductor to metallic under a compressive biaxial strain and a positive electric field. The hexagonal monolayer GeTe demonstrated potential for photocatalytic water splitting due to its suitable band edge positions. In addition, it was possible to tune the band edge positions by the external biaxial strain and electric field to improve the photocatalytic efficiency. The H2O-gas sensing properties of monolayer GeTe and the inner mechanisms of charge transfer were investigated. In the case of H2O-adsorbed Ge-top hexagonal monolayer GeTe, the charge transfer reached 0.056 e under compressive strain of −4%, which is significantly greater than that for most other 2D materials. [ABSTRACT FROM AUTHOR]

The existence of a variety of two-dimensional (2D) carbon allotropes with different carbon frameworks has provided an unprecedented platform to explore novel properties and potential applications beyond graphene. In this work, the strain effects on the structural, electronic, and thermal transport properties of the γ-graphyne and twin graphene sheets have been systematically clarified through first-principles calculations. Regardless of the geometrical similarities of the two considered 2D carbon allotropes, our results indicate that the acetylenic linkages in the γ-graphyne and the AA-stacked aromatic rings in the twin graphene are capable of resulting in the notable deviations in their electronic and thermal transport properties, as well as the strain-dependent behaviors. Both of the two sheets possess an intrinsic semiconducting nature with a tunable direct bandgap that depends on the biaxial strains. The thermal conductivity of the γ-graphyne is significantly suppressed compared to the twin graphene counterpart. Moreover, the heat transfer of the two sheets can be further enhanced by the tensile strains, and a dramatic increase can be obtained in the strained γ-graphyne sheet. Thus, the effectively tunable electronic and thermal transport properties revealed in this work imply the great potential of the two 2D carbon allotropes, and the comparative study also uncovers the structural effect of the carbon networks on their novel properties and strain responses. [ABSTRACT FROM AUTHOR]

First-principles calculations are performed for Mn4+-doped A2SiF6 (where A = K, Rb, and Cs) to investigate the influence of A-site cations on the geometric structures and optical transition energies of the 2E and 4T2 excited states. The geometric structures of the 4A2 ground state and the 2E and 4T2 excited states were successfully modeled using the delta self-consistent field (ΔSCF) method and their optical transition energies were evaluated for Mn4+-doped A2SiF6, which are in good agreement with the experimental values. Notably, the relationships between the zero-phonon line (ZPL) energy of the 4T2 state and the bond length of the Mn4+-F− bond are investigated in detail. The challenges of computational convergence were effectively addressed through the proposed fractional particle occupancy schemes for modeling the 4T2 state. The computational techniques developed in this study can be applied to other 3d3 activator ion/host matrix combinations, providing valuable insights into their structural and optical properties. [ABSTRACT FROM AUTHOR]

Inorganic lead-free metal halide perovskites are being rigorously explored as a substitute for organic lead-based materials for various energy device applications. Germanium as a replacement for lead has been proven to give exemplary results theoretically, and there have been promising results. The current work presents the investigation of CsGeI3 (CGI) polycrystals grown using a solution-free melt-growth technique with low-cost precursors. A soak-ramp profile was designed to synthesize polycrystalline powders, which were evaluated for stability. X-ray diffraction and Raman spectroscopy analysis suggest the formation of CsGeI3 perovskite powders, matching the reported literature. Diffuse reflectance spectroscopy measurements showed the bandgap of the polycrystals to be around 1.6 eV. A prominent photoluminescence peak was obtained at 767 nm. The powders were examined using thermogravimetric analysis to assess the thermal degradation pathways. The as-grown inorganic perovskite polycrystals were relatively stable during storage under ambient conditions. Theoretical studies were also carried out to support the experimental data. Calculations were performed with different approximations, including local density approximation (LDA), generalized gradient approximation (GGA), and Heyd–Scuseria–Ernzerhof (HSE) approximation, out of which the HSE approximation yielded the most accurate results that matched the experimental findings. Moreover, for the CGI device with Ag electrodes simulated using SCAPS-1D software, highest incident photon-to-electron conversion efficiency was observed. The obtained optical and structural properties indicate the suitability of the synthesized CsGeI3 perovskite polycrystals for photovoltaic applications, specifically solar cells and light-emitting diodes. [ABSTRACT FROM AUTHOR]

In this study, La0.63Sr0.2Nd0.17MnO3 was synthesized by the sol-gel method, and its structural, morphological, magnetic, and magnetocaloric effects were investigated. The structural properties were analyzed by x-ray diffraction (XRD), and scanning electron microscopy (SEM) was used to characterize the morphology. An integrated magnetic measurement system was used to determine the magnetic properties. La0.63Sr0.2Nd0.17MnO3 crystallized in a hexagonal crystal system with space group R-3c. This was also confirmed by Rietveld refinement of the x-ray data from La0.63Sr0.2Nd0.17MnO3. With the doping of Nd3+, the cell volume decreases, which can be explained by the angles and bond lengths of the bonds between the Mn and O ions and the distortion of the lattice. Near the Curie temperature, La0.63Sr0.2Nd0.17MnO3 exhibits significant magnetocaloric effects. The magnetic study of La0.63Sr0.2Nd0.17MnO3 suggests that the transition from the paramagnetic to ferromagnetic phase can occur near the Curie temperature. The maximum magnetic entropy change and relative cooling power (RCP) of La0.63Sr0.2Nd0.17MnO3 (298 K, 3 T) are 2.70 J/(kg K) and 135 (J/kg), respectively. The effect of f-orbitals on the magnetic properties of La0.8Sr0.2MnO3 was investigated by first-principles calculations in density functional theory. Thus, it can be concluded that the magnetocaloric effects of the material after doping with f-orbital ions (Nd3+) is enhanced compared to La0.8Sr0.2MnO3. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) semiconductors are widely regarded as promising contenders for the next generation of optoelectronics and microelectronics, rendering the development of novel 2D semiconductors a focal point in current research. In this study, our attention is directed towards the non-van der Waals material Cu6GeWS8, where we have successfully predicted a stable 2D monolayer, designated as 2D Cu6GeWS8. This monolayer exhibits a direct bandgap of 1.709 eV, which maintains its robustness under biaxial strain ranging from −4% to 3%. Remarkably, the monolayer Cu6GeWS8 showcases high hole mobility and demonstrates a moderate optical absorption coefficient across the visible and ultraviolet spectra. Notably, our investigation reveals that the monolayer Cu6GeWS8 possesses an exceptionally low lattice thermal conductivity of 0.593 W m−1 K−1 at room temperature. These findings underscore the excellent physical characteristics of the predicted monolayer Cu6GeWS8, positioning it as a promising candidate for advanced low-dimensional devices. [ABSTRACT FROM AUTHOR]

Hafnia has emerged as a promising material for charge-trapping memory. However, enhancing its trapping performance remains a significant research challenge. In this work, we investigate the influence of Bi impurities on the reliability of HfO2-based charge-trapping memory devices using first-principles calculations. By examining the impact of Bi impurities on the formation of oxygen vacancies (VO), we obtained the lowest-energy Bi-VO3 defect model. Through an exploration of the microstructure, electronic structure, and Bader charge distribution of the Bi-VO3 defect system, we compare its device performance with the Al-VO3 defect system. Our findings demonstrate that the Bi-VO3 defect system exhibits superior electronic retention ability compared to the Al-VO3 defect system. This suggests that introducing Bi impurities into HfO2 can enhance the reliability of memory devices and presents a promising dopant solution for improving memory performance. [ABSTRACT FROM AUTHOR]

We focus on the electronic, magnetic, and ferroelectric properties of the bilayer composite, Bi0.9La0.1Fe0.9Mn0.1O3/La0.8Sr0.2MnO3 (BFO-LM/LSMO). The studied films were processed on a Pt-substrate using chemical solution deposition. The morphology and structure purity of the synthesized films were characterized by field-emission scanning electron microscopy (FE-SEM) and x-ray diffraction (XRD). In addition, the simultaneous presence of macroscopic polarization and a fairly high magnetization were highlighted for the investigated specimen. In addition, the stability and electronic and magnetic properties of the BFO-LM/LSMO bilayer films with different stacking patterns have been explored using first-principles calculations. Moreover, the interfacial separation work for the Fe and Mn atoms at the interface in the BFO-LM/LSMO bilayer are 0.2069 J/m2 and 1.0309 J/m2, respectively, indicating that these systems have high stability, which is due to the strong hybridizations of the Fe_d, Mn_d, and O_p states at the interface. The interactions between the Fe and Mn spins at the interface lead to enhancing the remnant and saturation magnetizations in this system. The obtained results make BFO-LM/LSMO films a promising material for advanced spintronics and multifunctional devices. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) tungsten disulfide (WS2) is attracting increasing attention because of its excellent physical properties. However, the phonon scattering mechanisms of 2D T′-phase WS2 (T′-WS2) are still poorly understood. In this paper, we systematically evaluate the phonon thermal transport properties of monolayer T′-WS2 under different biaxial tensile and compressive strain using first-principles calculations. The lattice thermal conductivity (kl) of monolayer T′-WS2 decreases monotonically with the increase in biaxial strain. The largest reductions are 97.84% (7% tensile strain) and 65.41% (−3% compressive strain). The kl of monolayer T′-WS2 is dominated by acoustic phonon modes and a portion of optical phonon modes (0–8 THz). Moreover, from the analysis of phonon behaviors, the reduction in the kl of monolayer T′-WS2 under biaxial tensile strain is attributed to the decrease in phonon heat capacity, phonon group velocity, and phonon lifetime. However, for the biaxial compressive strain, the reduction in the kl can be attributed to the interaction among the increased phonon heat capacity, relatively complex changes in the phonon group velocity, and the reduced phonon lifetime. Therefore, according to the variations in phonon phase space and Grüneisen parameters, it is evident that the biaxial tensile strain does not have a significant effect on the phase space of monolayer T′-WS2, whereas it has a significant effect on the Grüneisen parameter. This investigation offers valuable insight into the thermal conduction behavior of 2D monolayer T′-WS2. [ABSTRACT FROM AUTHOR]

Recent investigations have demonstrated that transition metal dichalcogenides (TMDs) are excellent candidates for water-splitting photocatalysis to produce hydrogen energy, but they exhibit a high recombination rate of photogenerated charge carriers, which hinders their practical application. Constructing novel TMD-based van der Walls (vdW) heterostructures is a promising strategy to suppress charge recombination, providing an opportunity to uncover new photocatalysts with improved water-splitting efficiency. In this work, we investigate the structural, optoelectronic and photocatalytic properties of the most favorable stacking pattern of SiC-VXY (X = Cl, Br and Y = Se, Te) vdW heterostructures using first-principles calculations. The results indicate that SiC-VXY (X = Cl, Br and Y = Se, Te) vdW heterostructures exhibit an indirect bandgap with type II band alignments, which effectively separate photoexcited electron-hole pairs at the interface. Moreover, the band edge positions of SiC-VXY bilayer systems straddle the redox potential of water, indicating that these heterostructures have the potential to become efficient photocatalysts for water splitting. Our theoretical investigation provides certain basis for designing novel TMD-based water-splitting photocatalysts and can pave the path for future experiments. [ABSTRACT FROM AUTHOR]

An anisotropic nature and layer-dependent bandgap energy are the unique properties that make phosphorene an attractive two-dimensional (2D) material to explore. Tremendous interest in unraveling other properties of phosphorene find application in energy conversion, photodetectors, electronic and optoelectronic devices, and gas sensing. The structural and dynamical stability and mechanical and electronic properties of phosphorene-like indium triphosphide monolayer (InP3) are compared to pristine phosphorene (PP). Gaseous molecules of carbon dioxide (CO2), carbon monoxide (CO), nitrogen dioxide (NO2), nitrogen oxide (NO), hydrogen sulfide (H2S), sulfur dioxide (SO2), and ammonia (NH3) are adsorbed on phosphorus (P), indium (In), and hollow (H) sites. The adsorption energies, differential charge densities (DCD), and electronic band structures of all molecules on each site are investigated. The adsorption energies of small gas molecules on the InP3 monolayer show better performance than pristine phosphorene (PP) and indium-doped phosphorene (In@P). The computed adsorption energies of NO and NO2 are −0.849 eV and −1.168 eV. The results prove that the most favorable adsorption site is on the top of the In atom. Therefore, the InP3 monolayer is more sensitive to the NO2 molecule. [ABSTRACT FROM AUTHOR]

For two-dimensional transition metal dichalcogenides, the thermoelectric properties of the material are affected by layer thickness and lattice strain. In this paper, we investigate the thermoelectric properties of a HfS2 bilayer under different biaxial tensile strains by first-principles calculations combined with Boltzmann equations. The presence of degenerate bands in the HfS2 bilayer and the absence of its monolayer results in the better thermoelectric performance of the HfS2 bilayer than its monolayer. Moreover, this strain increases the band degeneracy of the HfS2 bilayer even more, and the degenerate bands and stepped 2D density of states lead to a high power factor. In addition, the lattice strain increases the phonon scattering rate and reduces the phonon lifetime of the HfS2 bilayer, resulting in a decrease in the lattice thermal conductivity. Ultimately, we obtained a maximum ZT value of 1.76 for the unstrained HfS2 bilayer at the optimal doping concentration. At this time, its power factor and thermal conductivity are 53.01 mW/mK2 and 9.06 W/mK, respectively. When the strain reaches 3%, for the n-type doped HfS2 bilayer, the power factor and thermal conductivity are 69.87 mW/mK2 and 6.36 W/mK, respectively, and the maximum ZT value is 3.29. For the p-type doped HfS2 bilayer, the maximum ZT value appears at 6% strain, which is 1.83, at which the power factor and thermal conductivity are 13.81 mW/mK2 and 2.27 W/mK, respectively. [ABSTRACT FROM AUTHOR]

Compared with traditional thermoelectric (TE) materials, bismuth oxyselenide (Bi 2 O 2 Se) consists of nontoxic and lower-cost elements and has better chemical and thermal stability. The highest ZT value of Bi 2 O 2 Se ever obtained experimentally was recently reported at 0.69. To further improve its TE performance, the electron and phonon transport properties of intrinsic n-type Bi 2 O 2 Se are evaluated by first-principles calculations. Due to the density of states at the conduction band minimum being too small resulting in a low intrinsic carrier concentration, the reported TE properties of Bi 2 O 2 Se are not ideal. The TE parameters we calculated are in good agreement with the experimental values. The average optimal ZT values at 800 K for the p-type and n-type Bi 2 O 2 Se are 1.83 and 1.81, respectively, indicating that Bi 2 O 2 Se is a promising TE material. It is an innovative approach to improve the TE performance by regulating the vacancy defects in Bi 2 O 2 Se, which could achieve the cooperative optimization of electrons and phonons through the energy filtering effect and enhanced phonon scattering. Our results could provide a theoretical basis for further improving the TE properties of Bi 2 O 2 Se in experiments. [ABSTRACT FROM AUTHOR]

This article presents a demonstration of the significant impact that the atomic masses of constituent atoms and the isotopically pure and heavy property of a constituent atom have on the thermal conductivity in the zinc blende crystal structure of semiconductor materials. We take boron arsenide and gallium arsenide from the semiconductors of groups (iii - v) as well as cadmium selenide and cadmium telluride from the semiconductors of groups (ii - vi) . Thermal conductivity is acquired by using the first-principles calculation technique and the Boltzmann transport equation with the relaxation time approximation. The corresponding thermal conductivity of CdSe and CdTe are 7.58 Wm - 1 K - 1 and 5.27 Wm - 1 K - 1 at room temperature (300 K) , which is significantly lower than that of BAs. We performed calculations of phonon scattering, group velocities, relaxation time, mean free path, and the mode Grüneisen parameter to investigate such differences in their thermal characteristics. The outcomes of our research have the potential to enhance our understanding of the mechanisms of heat transfer in BAs, CdSe, CdTe, and GaAs, and to validate the criteria for identifying semiconductor materials with high thermal conductivity, thereby enabling the design of more efficient nano-electronics. [ABSTRACT FROM AUTHOR]

We investigate the impact of polarons on Mo around the oxygen vacancy on the electronic structures and optical properties of SrMoO4 crystals. The screened hybrid density function within the Kohn–Sham density functional theory combined with the finite-size correction are employed in our calculations. Results indicate that the trapped electrons in the form of polarons are all localized on the same Mo atom which is nearest to oxygen vacancy V O × or V O ′ , not on the oxygen vacancy. Optical spectra of polarons around the oxygen vacancy are also obtained. The calculated absorption peaks (4.38 eV) and emission peaks (2.85 eV) are in line with the experimental results, thus providing insight into the origin of the blue luminescence spectra of the SrMoO4. [ABSTRACT FROM AUTHOR]

Recently, derivatives of molybdenum disulfide have attracted considerable attention. Among them, the thermal conductivity of Janus-based MoSSe SeS, SeSe and SS bilayers has not been investigated. Along these lines, in this work, the lattice thermal conductivities of Janus MoSSe-based bilayer structures were examined. More specifically, three different combined modes were used, including SMoSe/SMoSe (SeS stacking), SMoSe/SeMoS (SeSe stacking) and SeMoS/SMoSe (SS stacking), based on first-principles calculations. The extracted results show that the lattice thermal conductivity of all three structures is decreased with increasing temperature, whereas the SeS structure has a maximum lattice thermal conductivity value of about 22 W/mK at 300 K. The SS structure exhibits also the strongest phonon anharmonicity and highest phonon scattering effects, which leads to the smallest lattice thermal conductivity value of about 1.57 W/mK in the x-direction at room temperature, rendering the proposed configuration well suited for thermoelectric applications. [ABSTRACT FROM AUTHOR]

Nodal-loop semimetals are novel quantum materials that have attracted considerable research interest from scholars for their fascinating properties due to the band crossing characteristic. Nevertheless, nodal loop semimetals in two-dimensional (2D) lattices are quite rare. Here, we report our new discovery of a Zn4C2 monolayer with a P4/mmm symmetry tetragonal lattice that possesses a robust Dirac nodal-loop state, using first-principles calculations. Further calculations show that the gapless nodal-loop is protected by the horizontal mirror symmetry, which can be well maintained at external strains between -8% and 8%, and is also robust against the choice of Ueff for correlation effect and the choice of functional. The results of this paper reveal a new type of novel 2D Dirac nodal-loop material, which provides a new potential material for high-speed electronic devices. [ABSTRACT FROM AUTHOR]

Heusler materials have shown a ground-breaking role in material research because of their widespread applicability in modern technologies and multi-dimensional properties. In this study, the pressure effects on the structural, electronic, and magnetic properties of Mn2YAN (Y = Ru, Rh, and Pd) Heusler alloys are investigated. This study is carried out by employing a state-of-the-art first-principles computational approach called "full potential (FP) linearized (L) augmented plane wave plus local orbital (APW + lo)" as designed using density functional theory (DFT), and executed in WIEN2k computational code. The computed results for the lattice constants have been found to be in fairly good agreement with previously reported results in the literature. The results show that the Mn2RuSn, Mn2RhSn, and Mn2PdSn compounds are stable in the Hg2CuTi-type structure. Furthermore, under the pressure effect, the Mn2RuSn, Mn2RhSn, and Mn2PdSn compounds become half-metals at about 10 GPa, 10 GPa, and 20 GPa, respectively. [ABSTRACT FROM AUTHOR]

First-principles total energy calculations were performed to study the stability of Rh2TMSn (TM=Cr, Mn and Fe) toward different magnetic ordering, ferromagnetic (FM), antiferromagnetic type I (AFM-I) and antiferromagnetic type II (AFM-II). We studied the effects of electron correlation on the magnetic stability of the compounds in both cubic and tetragonal structures using density functional theory (DFT) within the generalized gradient approximation (GGA) and GGA+U. The results show that the electron correlation has an important role in determining the magnetic stability of the compounds. The magnetic stability obtained from GGA+U agrees well with the available experimental results. The thermodynamic stability of the three compounds shows that all the compounds are stable in both cubic and tetragonal structures. Using the energy difference method, we were able to calculate the exchange interactions and estimate the Curie temperature of the Rh2MnSn compound in the cubic structure. The phonon dispersion curves were investigated for the first time using the linear-response approach in the context of density functional perturbation theory. The results show that all the compounds are dynamically stable in their predicted phases. [ABSTRACT FROM AUTHOR]

In this work, we performed a first-principles calculation to investigate the effect of intrinsic defects on the electronic structure and magnetic properties of SrO crystals in detail. The calculated results show that intrinsic defects do not cause obvious lattice distortion and they can introduce impurity energy levels in the forbidden band of SrO crystals. The defect states originate from O-2p or Sr-4d states, which may become electron (hole) trapping centers or form an acceptor level in the forbidden band. However, different defects induce different magnetic moments. The magnetic moments of SrO with Vsr, Osr, SrO and Oi are 1.85 μB, 3.11 μB, 1.64 μB and 1.68 μB, respectively, while VO and Sri do not lead to a magnetic moment in the SrO crystal. It is found that the magnetic moment mainly arises from the spin polarization of O-2p and Sr-4d orbital electrons of defective atoms and their nearest neighbor atoms. Without considering Vsr here, Osr and Oi are the most stable defects in the SrO crystal under O-rich conditions while VO is the most stable defects under Sr-rich conditions. We suggest that the magnetism in SrO with intrinsic defects most likely originate from Osr and Oi. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) heterostructures show potential application as electrode materials in rechargeable batteries because of their appropriate electronic and energy storage properties. Herein, by employing density functional theory calculations, we consider performance of 3D graphene–WS2 nanoribbon (3DGW) hybrid structures as electrode materials for Mg-ion batteries. It is found that graphene can increase the Mg adsorption energies on the 3DGW surface with respect to the WS2 nanoribbon which can improve cycling stability. The calculated activation barrier of Mg diffusion on the 3DGW surface in the range of 0.47 eV and 0.51 eV, the average open-circuit voltage 0.86 V as well as the metallic conductivity of Mg@3DGW ensured excellent kinetic properties and electronic conduction of 3DGW for use as battery electrodes. The above findings confirmed that the 3DGW is a very promising electrode material for Mg rechargeable ion batteries. [ABSTRACT FROM AUTHOR]

The electronic and sensing properties of monolayer GeSe with the adsorption of various gas molecules (H2O, CO, NH3, NO, and NO2) under a vertical external electric field ranging from −0.8 V/Å to 0.8 V/Å were investigated by using first-principles calculations. The bandgaps of the pristine and gas-adsorbed systems all decreased in the presence of electric fields, especially a negative field. At the same time, the negative electric field caused two and one impurity states in the band gap of CO- and NO2 -adsorbed monolayer GeSe, respectively, which played an important role in manipulating the optoelectronic properties of the materials. By enhancing the adsorption ability and charge transfer, applying a relatively strong negative electric field can effectively improve the sensitivity of monolayer GeSe to NH3 molecules. Therefore, an external electric field is highly preferred and provides a practicable approach for controllable monolayer GeSe-based electronic devices and gas sensors. [ABSTRACT FROM AUTHOR]

With the rapid evolution of microelectronics, the field of integrated circuits is facing unprecedented challenges. Traditional silicon-based transistors cannot maintain the advantages of high performance during the process of further ultra-scaling due to severe short-channel effects. Two-dimensional (2D) materials are potential channel materials that can replace silicon. Herein, 2D SiP is predicted to have a band gap of 1.49 eV with anisotropic electronic properties by means of first-principles calculations, which is suitable as a channel candidate of transistors. Hence, we investigate the ballistic transport properties of 2D SiP double-gate metal oxide semiconductor field-effect transistors (MOSFETs) by using ab initio quantum transport simulations. Despite anisotropic electronic properties of 2D SiP, the performances of monolayer SiP MOSFETs have weak directional dependence due to high valley degeneracy. The n-MOSFETs with 10-nm gate length can fulfill the high-performance requirements of the International Roadmap for Devices and Systems 2020 Edition (IRDS 2020). However, the p-MOSFETs cannot fulfill the demands of IRDS 2020 because of heavy hole effective masses. Considering the appropriate on-current of 1292 μA/μm for SiP n-MOSFETs, 2D SiP could be utilized as a potential channel material in the next-generation FETs. [ABSTRACT FROM AUTHOR]

Chemical modification can effectively control the quantum spin Hall (QSH) state by changing the lattice constant or topological phase transition. We functionalized ultraflat stanene with hydrogen and halogens on a single side (s-SnX) and both sides (b-SnX). It was found that the buckled heights of the neighboring Sn atoms for s-SnX were still zero, while b-SnX changed into a buckled structure, which is consistent with previous studies. In this work, the electronic and topological properties of s-SnX (X = H, F, Cl, Br, I) were mainly studied based on first-principles calculations. We predicted that s-SnF, s-SnCl and s-SnBr would be topological insulators (TIs). It was found that the band structures of s-SnF, s-SnCl, s-SnBr have s-p band inversions and semimetal-to-semiconductor transitions considering spin orbit coupling (SOC) with the largest band gap of 0.25 eV. The edge bands of calculating the edge states cross linearly, and the numbers of edge bands passing through the zero energy level between –X and Γ point are odd, indicating that s-SnF, s-SnCl and s-SnBr are TIs. Ultraflat stanene functionalized by hydrogen and halogen atoms can effectively control QSH states. It is proved that functionalization provides more choices for topological insulator materials and topological device applications. [ABSTRACT FROM AUTHOR]

Physical properties and thermodynamic properties of α-CoSn3 and β-Sn/α-CoSn3 interface were studied by first-principles calculations. The results show that α-CoSn3 can be classified as a brittle material. The volume, bulk modulus, coefficient of thermal expansion, Debye temperature, and heat capacity of α-CoSn3 were obtained using the quasi-harmonic Debye model. For (100) β-Sn/(600) α-CoSn3 interface, we found that cracks are prone to initiate at the interface or in the β-Sn bulk near the interface. The interfacial bonding properties were also analyzed according to the different charge densities and partial density of states, which indicated that Sn-Co interaction is characterized by covalent bonding, while Sn-Sn interaction is characterized by metal bonding. [ABSTRACT FROM AUTHOR]

More research work has focused on device structure preparation, doping modification, and interface control of CsPbI2Br-based solar cells, whereas less basic theoretical research has been carried out on CsPbI2Br-based perovskite solar cells. It is necessary to find a suitable method to accurately describe the microscopic properties of CsPbI2Br-based perovskite solar cells. Therefore, this paper starts from the interface regulation of all-inorganic perovskite CsPbI2Br to study in detail the local lattice and electronic properties of the light-absorbing layer (CsPbI2Br)/electron transporting layer (SnO2) heterogeneous interface at the atomic and electronic levels by using first-principles calculations based on density functional theory (DFT). The results show that the lattice mismatch at the CsPbI2Br (100)/SnO2 (110) heterogeneous interface is 6.4% while the interface binding energy is −0.79 J/m2, indicating that the interface orientation and bonding modes can exist stably. Density of states (DOS) calculations reveal that the CsPbI2Br (100)/SnO2 (110) interface presents some interface states caused by I 5p and O 2p orbitals near to the Fermi level, which is one of the reasons for the low conversion efficiency of such solar cells. [ABSTRACT FROM AUTHOR]

We predicted the electronic structure and half-metallic properties of the Mn2XSb (X = Co, Fe) inverse Heusler alloys using the full-potential linearized augmented plane wave (FPLAPW) method. We used generalized gradient approximation (GGA) and GGA + U schemes to compute the electronic structure for both alloys. We employed the Tran and Blaha modified Becke–Johnson (TB-mBJ) potential to accurately estimate the band gap. The stability has been determined by calculating their formation energy and elastic constants under ambient conditions. Both alloys show a half-metallic ferromagnetic nature with a 100% spin polarization at the Fermi level. The calculated total spin magnetic moments of Mn2XSb (X = Co, Fe) alloys are 4 μ B and 3 μ B , respectively, which is a good agreement with the well-known Slater–Pauling rule of 24. The predicted Curie temperature for both alloys is greater than room temperature. The half-metallic and high spin polarization properties make them one of the promising candidates for spintronic device applications. [ABSTRACT FROM AUTHOR]

Quaternary chalcogenides based on stannite I-II 2 -III-VI 4 structure are the best potential candidates to overcome the current generation of solar harvesting materials. First-principles electronic structure simulations were performed on semiconducting CuZn 2 Ga(S/Se) 4 (CZGS/Se) to understand the inter-relationship of the structural properties. These structures contain a cubic close packing (ccp) array of S/Se-centered tetrahedrons, coordinated by one Cu, two Zn and one Ga atom occupying one half of the ccp tetrahedral voids. The remarkable variations in the crystal structures are explained by the influence of ionic radii of various atoms. The electronic and optical properties calculated using hybrid functional (Heyd, Scuseria and Ernzerhof, HSE06) show a suitable band gap of 1.59 eV for CZGSe with high optical absorption. The current density and maximum upper limit of theoretical energy conversion efficiency (P(%)) of CZGSe is enhanced when compared to that of CZGS. Our results suggest that the stannite CZGSe structure could be a promising candidate for efficient earth-abundant thin-film solar cell applications. [ABSTRACT FROM AUTHOR]

Tungsten disulfide (WS2) has attracted great attention for use in optoelectronics due to its suitable bandgap and adjustable properties. However, the structure and photoelectric properties of bulk WS2 are not well understood. The first-principles method is applied herein to study the structural stability and electronic and optical properties of WS2. Two phases, viz. hexagonal and rhombohedral, are considered. The results reveal that the two bulk WS2 phases are thermodynamically and dynamically stable based on the enthalpy of formation and phonon dispersion. The structural stability of WS2 is attributed to the S–W–S sandwich structure. The calculated bandgap of hexagonal and rhombohedral WS2 is 1.552 eV and 1.488 eV, respectively, indicating that WS2 is semiconducting. The calculated optical properties show that WS2 exhibits excellent adsorption capacity for ultraviolet light, whether in the hexagonal or rhombohedral structure. [ABSTRACT FROM AUTHOR]

The development of high-efficiency anode materials with large capacity, high stability and fast diffusion rates is a key requirement for rechargeable Li-ion and Na-ion batteries (LIBs/NIBs). In this work, the adsorption and diffusion of Li and Na atoms on two-dimensional (2D) Si3N materials is studied using first-principles calculations. The Si3N monolayers have large adsorption energies (2.74 eV for Li and 2.17 eV for Na) and a high theoretical capacity (1772.0 mAh/g for Li and 859.6 mAh/g for Na). Moreover, the low diffusion barriers (0.45 and 0.24 eV) for Li and Na atoms indicate that Si3N has an excellent high charge/discharge capability. In addition, molecular dynamics simulations showed that the structure of the 2D Si3N monolayer with adsorption of 32 Li/Na atoms has a very small change at 400 K due to the large adsorption energies for Li/Na. Owing to its good features, the Si3N monolayer is a highly promising anode material for energy storage devices. [ABSTRACT FROM AUTHOR]

The effects of substitution of Au for Cu on the elastic, thermodynamic, and electronic properties of hexagonal η-Cu6Sn5 intermetallic compound (IMC) are investigated by first-principles calculations. The results show that Au atoms preferentially occupy Cu4 or Cu3 site to form η-Cu5Au1Sn5 or η-Cu4Au2Sn5 IMC, respectively. Doping Au in η-Cu6Sn5 IMC forms a more stable thermodynamic structure than pure phase. The ductility of η-Cu6Sn5 IMC increases after substitution of Au for Cu. However, doping Au weakens the Young's modulus, shear modulus, hardness, and Debye temperature of η-Cu6Sn5 IMC. The results for the charge density difference, total density of states, and partial density of states show that doping Au atoms can stabilize the structure of η-Cu6Sn5 IMC. [ABSTRACT FROM AUTHOR]

The structural, mechanical, thermodynamic, and electronic properties of PdSn4 with Ni addition are investigated by first-principles calculations. Substitution of Ni for Pd in PdSn4 causes a decrease of the lattice constants as well as cell volume due to the smaller atomic radius of Ni compared with Pd. The studied structures are thermodynamically stable, but the stability decreases with increasing Ni concentration. The bulk modulus increases while the shear modulus, Young's modulus, hardness, Debye temperature, and minimum heat transfer ability decrease on Ni substitution. PdSn4 is elastic–brittle. Substitution leads to a ductile structure, and the ductility increases with the Ni fraction except for Pd2Ni2Sn16. The anisotropic character is estimated both based on the formula and graphically, revealing an increasing anisotropic tendency after substitution. Based on their total density of states, all the compounds are metallic. Substitution decreases the hybridization of Pd-d and Sn-p states in the lower energy range but increases the hybridization of Ni-d and Sn-p electrons near the Fermi level. [ABSTRACT FROM AUTHOR]

Although ZrO2 is a promising advanced functional material, the influence of oxygen vacancies (O-va) on the structural stability and electronic properties of monoclinic ZrO2 is unclear. In particular, the role of O-va on the optical properties of ZrO2 is not well understood. Here, we apply the first-principles approach to investigate the role of O-va on the structure, electronic and optical properties of ZrO2. Two ZrO2 phase: monoclinic and cubic structures are considered. The results show that the O-va is thermodynamically stable in both monoclinic and cubic structures. In particular, O-va-mono is more thermodynamically stable than O-va-cubic. The O-va improves the electronic properties of ZrO2 because of the role of the Zr-4d state and the O-2p state near the Fermi level. Importantly, the O-va widens the adsorption range of ZrO2. Therefore, we believe that oxygen vacancoes are beneficial for improving the electronic and optical properties of ZrO2. [ABSTRACT FROM AUTHOR]

In the present work, we consider systematically the electronic and optical properties of two-dimensional monolayer germanium monosulfide (GeS) under uniaxial strains along armchair (AC-strain) and zigzag (ZZ-strain) directions. Our calculations show that, at the equilibrium state, the monolayer GeS is a semiconductor with an indirect band gap of 1.82 eV. While monolayer GeS is still an indirect band gap semiconductor under ZZ-strain, an indirect–direct energy gap transition can be found in the monolayer GeS when the AC-strain is applied. The optical spectra of the monolayer GeS have strong anisotropy in the investigated energy range from 0 eV to 8 eV. Based on optical properties, we believe that the monolayer GeS is a potential candidate for applications in energy conversion and optoelectronic technologies. [ABSTRACT FROM AUTHOR]