PBE Methods Research Articles

Ab initio investigation of structural, elastic, dynamic, and electronic properties of YN binary rare earth nitride in ZB cubic phase

This research employs ab initio calculations, utilizing the FP-LAPW method as implemented in WIEN2k and the PP-PW method in QUANTUM ESPRESSO, within the framework of the GGA-PBE approximation, to investigate the physical properties of the rare earth nitride binary YN. Structural parameters of YN are determined, yielding predictive results consistent with recent calculations. Furthermore, a comprehensive investigation into mechanical behavior and elastic properties confirms the mechanical stability of YN in its cubic ZB structure. An analysis of the anisotropy coefficient reveals its elastic anisotropy. The dynamic stability of YN is investigated through PW-scf calculations using DFPT theory, enabling the calculation of phonon spectra, frequencies, and polarization vectors. These findings affirm the stability of YN material in the B3 structure, which can be experimentally synthesized. Electronic properties are probed, showing semiconductor behavior, utilizing GGA mBJ, and YS PBE0 methods to ascertain band gap values in the B3 structure. This suggests its potential for adoption in optoelectronic and photonic devices.

Comparative properties of ZnO modified Au/Fe nanocomposite: electronic, dynamic, and locator annealing investigation.

A computational representation was used to model the doping and nanomodification of ZnO nanoparticles incorporated in Au/Fe nanocomposite. Au/Fe nanostructure was geometrically and discussed to investigate its electronic properties such electronic band structure and PDOS spectra. Moreover, the ZnO interacted with Au/Fe system was illustrated concerning the modified properties present on the surface of the nanocomposite as it may behave different attribution of band gap evaluated after ZnO modification included. Molecular dynamic simulation of the whole nano system was studied to predict the system stability concerning temperature and energy parameters during 100 ps simulation time. The most effective models under investigation were evaluated using adsorption annealing computations associated with the adsorption energy surface. A highly stable energetic adsorption system was anticipated by the periodic adsorption-annealing calculation. Au and Fe pure metals nanostructures were studied as a separate molecule with (0 0 1) plane surface for optimum energy minimization. Dmol3 module in/materials studio software was utilized for this protocol. The designed Au/Fe layers for nanostructure building material was computationally optimized, where DFT level was considered involving generalized gradient approximation (GGA) with Perdew-Burke-Ernzerh (PBE) exchange functional. In the computations of the structure matrix simulation, the global orbital cutoff was selected. To address the weak quantification of the standard DFT functionals, Tkatchenko-Schefer (TS) (DFT + D) was utilized to precisely correct the pairwise dispersion of the functionals. The electrical parameters were interpreted using the reciprocal space of the ultrasoft pseudopotential representation. To overcome the issues of self-electron interaction, the nonlocal hybrid functional with PBE0 method was utilized to calculate the electronic properties of the studied systems. The computations generated are predicated on a particular trajectory of the gamma k-point band energy interpolations proposed in this examination. An investigation into the position of adsorption came after geometric optimization. Adsorbed on an optimized Au/Fe surface, ZnO nanostructure was computationally explored using the Dmol3 simulation software.

First principle calculations to explore the electronic, mechanical and optical properties of 2D NiX2 (X = O, S, Se) monolayers

This investigation employs ab-initio calculations to investigate the structural, dynamical, mechanical, and optoelectronic attributes of 1T-NiX2 (X = O, S, Se) monolayers. The confirmation of structural and dynamical stability is derived from negative cohesive energy values and the absence of negative frequencies in phonon dispersion spectra. Mechanical stability is established through the application of the Born-Huang stability criterion. Results indicate that an increase in the X-atom size from O to Se induces a reduction in material stiffness from 137.64 Nm−1 to 77.56 Nm−1 and thus, enhances the flexibility of the monolayers. The NiX2 monolayers exhibit indirect bandgap features with values 1.33 eV (1.81 eV), 0.63 eV (0.61 eV) and 0.28 eV (0.28 eV) using PBE (PBE+U) methods. Present results show an inverse relations between the band gap and the size of the X atom. The scanning tunnelling microscope (STM) images of 2D NiX2 monolayers are also simulated for experimental observations. Additionally, exploration of optical characteristics reveals high optical absorption (105 cm−1), which lies from infrared to UV-region. Moreover, NiO2 can be utilized as good wave anti-reflectors with reflection of incident light less than 7%. These results suggest NiX2 materials as promising candidates for diverse applications in optoelectronic and photovoltaic devices.

Solid state synthesis, structural, DFT and spectroscopic analysis of EuAl3(BO3)4

Huntite-like borates are versatile and promising materials with wide range of applications in frequency conversion, UV light generation, lighting, displays, quantum information storage, and more, demonstrated by their various properties and uses in scientific research. In this work, EuAl3(BO3)4 powder was prepared through multi-stage solid-state reaction method using high-purity starting reagents: Eu2O3, Al2O3 and H3BO3, considering a 20 wt% excess of H3BO3 to compensate for B2O3 volatilization. Obtained samples undergo several treatments at varying temperatures and their phase purity is subsequently verified through powder X-ray diffraction analysis. The scanning electron microscopy reveals that resulting EuAl3(BO3)4 powder consists of granules exhibiting irregular morphologies with dimensions of 0.5–8 μm. The electronic band structure of EuAl3(BO3)4, calculated using the GGA PBE method, reveals f-states of Eu near 4 eV. These states do not produce emphasized peaks on simulated absorbance spectra. Using of DFT + U for the f-states of Eu pushed up f-bands above 6 eV and the charge transfer from p-O to d-Eu was obtained (Egdirect = 5.63 eV, Egindirect = 5.37 eV using Ueff = 4 eV). The variation of Ueff has a weak influence on the position of the bottom of the conduction band. The experimental bandgaps of EuAl3(BO3)4 crystalline powder, both direct and indirect, are found to be 3.96 and 3.67 eV, correspondingly. These values are lower than theoretical values what is associated with limitations of DFT calculations involving f electrons. The Raman spectrum of EuAl3(BO3)4 powder is discussed, detailing the contributions of different ions to specific spectral bands. Investigation of high-resolution luminescence spectra shows the possibility to estimate the content of defects by the testing the violation of the prohibition of ultranarrow 5D0 → 7F0 line that is forbidden in the ideal crystalline structure of trigonal EuAl3(BO3)4.

Investigating of novel inorganic cubic perovskites of A3BX3 (A=Ca, Sr, B[dbnd]P, As, X=I, Br) and their photovoltaic performance with efficiency over 28%

Inorganic halide perovskite-based compounds of A3BX3 have been gaining huge attention during the development of high-efficiency solar cells (SC) in recent years. This paper, investigating the physical and chemical properties could unveil its further potential to be used as absorber materials in advanced multijunction photovoltaics. The structural, optical, and electronic characterization of different compositional compounds of A3BX3 (A=Ca/Sr, BP/As, X=I/Br) perovskites are examined thoroughly to be used as absorber in high performance photovoltaics. The DFT study reveals direct bandgaps of 1.93 (2.60) eV, 1.58 (2.14) eV, 1.96 (2.63) eV, 1.58 (2.16) eV, 1.52 (2.30) eV, 1.26 (1.94) eV, 1.53 (2.32) eV, and 1.26 (1.96) eV at Γ for the Ca3AsBr3, Ca3AsI3, Ca3PBr3, Ca3PI3, Sr3AsBr3, Sr3AsI3, Sr3PBr3, and Sr3PI3 perovskites using PBE (HSE) methods with optical absorption of (2−5)x104 (a. u.) in the optical region (< 3.2 eV). Subsequently, the potential of the A3BX3 absorber has been investigated and analyzed at varying layer thickness, defect densities, and doping concentrations with SnS2 electron transport layer (ETL) layer using FTO/SnS2/A3BX3/Ni heterostructure with current density-voltage (J-V) characteristics and corresponding quantum efficiency (QE) observation. The power conversion efficiency (PCE) of 13.52, 20.88, 13.66, 22.47, 20.83, 28.16, 20.77, and 27.32% were achieved in Ca3AsBr3, Ca3AsI3, Ca3PBr3, Ca3PI3, Sr3AsBr3, Sr3AsI3, Sr3PBr3, and Sr3PI3 absorber-based heterojunction SC. Notably, the highest PV performance revealed a PCE over 28% with a VOC of 0.913 V, JSC of 35.75 mA/cm−3, and FF of 86.26% obtained in the Sr3AsI3 absorber SCs. Thus, these detailed studies on the physical and optoelectronic properties of eight (8) different possible absorber-based configurations including their PV applications unveil the huge potential of A3BX3 (i.e., Sr3AsI3) and provide resources for the practical cell development of inorganic perovskites-based high efficiency SC over 28%.

Hg-Hg bonding and its influence on the stability of (HgS)n clusters.

Pulsed laser ablation of a HgS(s) precursor shows the formation of small cluster ions, (HgS)n=2-4+, together with HgSn=1-8± and [(HgS)n + Sm]±. The computed structure, atomization energy, and HOMO-LUMO gap energy values of the lowest energy ring singlet show stable (HgS)n=2-8. However, the computed bond conductance of the Hg-Hg bond in (HgS)n shows a high value for (HgS)n=2-4 (ξ = 1.072-0.122), whereas it is low for (HgS)n=5-8 (ξ = 0.039-0.006) and decreases significantly as the ring expands, indicating that (HgS)n≥5 is unstable. It evidences that the weak chemical bonding between Hg2+-Hg2+ closed shell (5d10-5d10) electrons plays a significant role in the stability of ring (HgS)n=2-4. Thus, it validates the experimental observation of stable cluster ions up to (HgS)4+. In contrast, the low energy chain triplet (HgS)n=2-8 shows a progressive increase in stability and bond conductance with chain length, indicating sustained mercurophilic interactions in long chain clusters like its crystal structure. Furthermore, the lowest/low energy isomers of HgSn=1-8 have been computed for their energetics, HOMO-LUMO gaps, and electron affinity using DFT-B3LYP/PBE0 methods.

1H,4H‐1,4‐diborabuckminsterfullerene with pyridine molecules and ytterbium endo‐atom

AbstractThe competition between the ytterbium endo‐atom and the pyridine exo‐molecules as nucleophiles interacting with the electron‐deficient 1H,4H‐1,4‐diborabuckminsterfullerene was studied using the quantum chemical DFT PBE0 method. The equilibrium structural parameters, dipole moments, IR spectra, and exothermic effects of the formation of the C58B2•Py2 adduct and the endohedral Yb@C58B2•Py2 complex were determined. The concept of the state of oxidation/reduction of an atom in a chemical compound has been clarified. The localization of the ytterbium(II) under a pair of equivalent carbon atoms bonded to boron(III) atoms is predicted. The introduction of ytterbium(II) into the adduct cavity weakens exo‐bonds with pyridine molecules without changing the oxidation state of boron(III). Each nitrogen atom retains a lone electron pair, coordinated by a boron(III). The ytterbium(II) endo‐atom retains 14 electrons in f states.

Advancing photovoltaics and optoelectronics: Exploring the superior performance of lead-free halide perovskites

One of the emerging directions that has greatly advanced the fields of photovoltaics and optoelectronics is the development of lead-free inorganic halide perovskites. In this study, ab-initio methods were employed to forecast the structural, electronic, and optical behavior of the perovskite materials Cs2Cu+Al3+X6 (where X represents Cl or Br). The analyses conducted have revealed the exceptional structural characteristics of these compounds. The electronic band structure and density of states were computed using the PBE method with the mBJ potential. The direct bandgaps of Cs2CuAlCl6 and Cs2CuAlBr6 were determined to be 1.35 eV and 0.93 eV, respectively. This suitable electrical bandgap results in high visible-light absorption. As a result, the optical characteristics exhibit a significant absorption coefficient (α(ω)≈1.1×105cm−1 for Cs2CuAlBr6 and 0.77 ×105cm−1 for Cs2CuAlCl6), substantial conductivity, and negligible reflectivity (R(ω) < 10%). These attributes render Cs2CuAlCl6 and Cs2CuAlBr6 semiconductors highly appealing for optoelectronic applications. The maximum spectral light conversion efficiency under AM1.5G solar irradiation was assessed by altering the thickness of the structures. The results reveal that the chlorinated perovskite achieves a slightly higher efficiency of 32.72%, whereas the brominated perovskite reaches an efficiency of 29.31%. Despite their remarkably advantageous bandgaps, limited reflectivity, and impressive efficiency, environmentally friendly halide perovskite compounds hold promise as renewable energy conversion materials. This suggests the potential for substantial enhancements in solar cell performance. Furthermore, employing the finite element (FE) method, we performed calculations to assess carrier generation within a specially engineered solar cell structure comprising an environmentally friendly multilayer (CH3NH3SnI3 and Cs2CuAlX6). Our discoveries unveiled an exceptionally elevated total generation rate at the interfaces between CH3NH3SnI3 and Cs2CuAlX6, reaching approximately 2.5 × 1029 m−3/s. These findings offer novel perspectives that contribute to the research community and hold the potential to advance future solar cell systems.

First principles prediction of geometrical, electronic, mechanical, thermodynamic, optical and photocatalytic properties of RaZrO3 scrutinized by DFT investigation

We have performed a thorough investigation of the RaZrO3 crystal's geometrical, electrical, mechanical, thermodynamic, and optical properties utilizing density functional theory (DFT). To calculate the energy gap widely recognized approaches PBE and B3LYP were employed and the result was found to be 2.29 and 4.06 eV respectively. Then Ra, Zr, and O atomic orbital nature of RaZrO3 was ascertained through rigorous analysis of total and partial state of density. The elucidation of bonding traits of RaZrO3 has been accomplished by calculating the Mulliken population charge. The mechanical and thermal stability of the RaZrO3 crystal, as well as its ductile and elastically anisotropic character, have been sustained. The optical characteristics of RaZrO3 crystal have been extensively investigated utilizing the PBE and B3LYP methods concerning energy and wavelength. Both techniques revealed conclusive evidence that RaZrO3 possesses exceptional absorption capabilities in the visible and ultraviolet spectrums. Ultimately, the amazing photocatalytic characteristics exhibited by crystals, render them very promising contenders for photo-catalysts capable of efficiently responding to visible light.

Modulation of electronic and optical properties of BlueP/MoSSe heterostructures via biaxial strain and vertical electric field

Constructing van der Waals heterostructures (vdWHs) is an efficient approach for enhancing the desirable properties of two-dimensional (2D) materials and greatly expanding the range of applications of the original monolayer materials. The structure, stability, electronic and optical properties of BlueP/MoSSe heterostructures are explored by density functional theory (DFT) calculations. The different configurations of BlueP/MoSSe vdWHs are all indirect bandgap semiconductors and have similar energy band structures, with the bandgap of about 1.0 eV under the PBE method. The bandgap of the A3 (B3) configuration calculated with HSE06 method is 1.608 (1.377) eV. The A3 configuration exhibits type-II band alignment while the B3 configuration shows type-I band alignment, both of which have high stability. The bandgap and band edge of A3 (B3) configuration can be modulated effectively by biaxial strain and vertical electric field (Efield). The BlueP/MoSSe vdWHs have broader absorption range and higher absorption intensity than their monolayers. The optical absorption intensity of heterostructures is gradually improved with increasing compressive strain, and the optical absorption spectrum is red-shifted under tensile strain. We hope that our findings will provide meaningful theoretical guidance for the preparation and potential application of BlueP/MoSSe vdWHs.

An efficient GaS/ XTe2 (X=W, Mo) vdW heterstructure photocatalyst for water splitting: The first-principles study

In this paper, the electrical and optical properties of GaS/MoTe2 and GaS/WTe2 van der Waals heterostructure are investigated by first-principles methods, and their properties are modulated by applying biaxial strain and doping. It was revealed that the unstrained GaS/MoTe2 and GaS/WTe2 van der Waals heterostructures is semiconducting with an indirect bandgap of 1.16 eV and 1.28 eV using PBE methods, and the direction of the built-in electric field of the heterojunction is XTe2 pointing to GaS, which is perfect for powerful light absorption. The bandgap widths of the two heterostructure are significantly reduced compared with that of monolayer materials. Besides, the results show that the biaxial strain is an effective tool for adjusting the energy gap where the indirect energy gap under the strain effects ranged within a range of 0.33/0.34 eV at −8% to 0.361/0.464 eV at 6%. At −8% compressive strain, the interfacial charge transfer reaches a maximum for each of the two heterostructure. In addition the absorption coefficients of GaS/MoTe2 and GaS/WTe2 heterostructure increase in the visible and infrared regions and the absorption spectral range is broadened. Therefore, GaS/MoTe2 and GaS/WTe2 vdW heterostructure can be applied in photocatalytic water decomposition and other fields.

Comparison between PBE-D3, B3LYP, B3LYP-D3 and MP2 Methods for quantum mechanical calculations of polarizability and IR-NMR spectra in C24 isomers, including a novel isomer with D2d symmetry

In this study, we have performed a comprehensive theoretical analysis of C24 isomers in the gaseous phase using the PBE-D3/cc-pVTZ, B3LYP/cc-pVTZ, B3LYP-D3/cc-pVTZ and MP2/6-31G methods. We have also considered the basis set cc-pVTZ for the MP2 method, and carried out optimized (single point) calculations in three isomers (in the remaining two isomers where the convergence was too time consuming) in order to reveal the potentiality of the method. Our investigation covered a wide range of properties, including geometry optimizations, chemical stability, polarizabilities, nuclear screening constants, Fermi (FE), gap (GE) and atomization energies (AE), thermodynamic analysis, reactivity index, as well as IR and NMR spectra. These calculations were performed for the ring (D12h), sheet (D6h) and two cage (D6d and Oh) configurations. Interestingly, we also proposed a new structure, the bracelet (D2d) arrangement, which appeared to be stable according to the PBE, B3LYP and B3LYP-D3 methods, but was classified as a transition state by the MP2 method. The results consistently indicated that the D6h isomer is the most stable one among the C24 isomers studied, while the D2d isomer was found to be the least stable. Regarding the gap energy (GE), the B3LYP and B3LYP-D3 methods consistently yielded higher values compared to the PBE’s, with an average DFT (PBE and B3LYP) GE of 1.89 eV, whereas the MP2 method showed a substantially higher GE value of 7.6 eV, representing an increase of approximately 75%. Additionally, the polarizabilities of the C24 isomers were found to be overestimated by the PBE, B3LYP and B3LYP-D3 methods when compared to the corresponding MP2 values. The PBE-D3 method consistently produced higher polarizabilities for the C24 isomers in comparison to the B3LYP, B3LYP-D3 and MP2 methods. The investigation confirms that the Oh (D12h) isomer has the smallest (largest) polarizability, as agreed upon by all methods. Moreover, the polarizability of D12h is notably affected by the selected DFT method, while that of Oh displays lower sensitivity but shares similarities with D6d. However, for the newly proposed D2d isomer, the polarizability is ranked third (fourth) in ascending order with the PBE-D3 (B3LYP-D3) method. This highlights the importance of considering the electronic correlation and dispersion effects in accurately predicting polarizabilities. The results obtained from the different methods shed light on the impact of the methodology choice on the predicted properties, emphasizing the need for careful consideration when analyzing and interpreting theoretical results for such various geometries.

First-principles studies on the structural, electronic and thermal transport characteristics of half-Heusler compounds LiXN (X=Mg, Zn)

The electronic structures and thermal transport properties of the half-Heusler (HH) compounds LiMgN and LiZnN are calculated in detail by combining first-principles calculations with Boltzmann transport theory. Our phonon calculations showed that LiMgN and LiZnN are dynamic stability. The calculated bulk moduli and equilibrium lattice constants are in good agreement with the experimental and available theoretical data. The electronic band structures obtained by PBE (HSE06) method indicate that both LiMgN and LiZnN are direct bandgap semiconductors with band gaps of 2.33 eV (3.23 eV) and 0.53 eV (1.42 eV), respectively. It is shown that the Li–N，Li–Mg and Li–Zn are ionic bond via ELF analysis. At room temperature, the calculated lattice thermal conductivities of LiMgN and LiZnN compounds are 19.31 Wm−1K−1 and 18.74 Wm−1K−1, respectively; But with the external temperature increases to 1100 K, their lattice thermal conductivities are decrease rapidly to 4.96 Wm−1K−1 and 4.32 Wm−1K−1, respectively. Moreover, we analyzed the mean free paths, phase volume spaces (P3), Gruneisen parameters (γ), scattering rates and group velocities in detail in order to further understand the origins of their relatively low lattice thermal conductivities and corresponding microscopic mechanism. We also investigated thermoelectric performances of LiMgN and LiZnN under different temperatures, and our results showed that with the external temperature increasing from 300 K to 1100 K, the maximum ZT values can increase from 0.05 (0.03) and 1.83 (1.32) for LiMgN (LiZnN), indicating that they are potential high-temperature thermoelectric materials. Our work can offer some theoretical references for improving thermoelectric performance and for future experimental studies.

Prediction of new stable crystal structures for ternary ErAgTe2 and YAgTe2 semiconductors: Ab initio study

The crystal structure, electronic, mechanical, and phonon properties of rare-earth ErAgTe2 and YAgTe2 compounds have been investigated using first-principles calculations based on density functional theory. We consider three different crystal structures: tetragonal (space group P 4‾ 21m, No. 113), orthorhombic (space group P212121, No. 19), and trigonal (space group P3m1, No. 156). The results indicate that all structures exhibit mechanical and dynamical stability with an anisotropic and ductile nature. The band gap is calculated using both PBE and HSE06 methods. The electronic properties of ErAgTe2 and YAgTe2 revealing the energy band gaps indicate that these compounds are semiconductors. The mechanical properties such as bulk, shear, Young's modulus, and Poisson's ratio were calculated. Finally, we explored the thermodynamic parameters, including the Debye temperatures and minimum thermal conductivities.

Raman spectra and vibrational properties of FOX-7 under pressure and temperature: First-principles calculations

FOX-7 (1,1-diamino-2,2-dinitroethene) as one of the widely studied insensitive high explosives exists five polymorphs (α, β, γ, α', ε) whose crystal structures have been determined by XRD (X-rays Diffraction) and which are investigated by a density functional theory (DFT) approach in this work. The calculation results show that the GGA PBE-D2 method can reproduce the experimental crystal structure of FOX-7 polymorphs better. The calculated Raman spectra of FOX-7 polymorphs were compared in detail and fully with the experimental Raman spectra data and it was found that the calculated Raman spectra frequencies have an overall red-shift in middle band (800–1700 cm−1), and that the maximum deviation does not exceed 4 % (The maximum point is the mode of CC in plane bending). The high-temperature phase transform path (α → β → γ) and the high-pressure phase transform path (α → α'→ε) can be well represented in the computational Raman spectra. In addition, crystal structure of ε-FOX-7 was performed up to 70 GPa to probe Raman spectra and vibrational properties. The results showed that the NH2 Raman shift is jittering with pressure (not smooth compared to other vibrational modes) and NH2 anti-symmetry-stretching appears red-shifted. The vibration of hydrogen mixes in all of other vibrational modes. This work shows that the dispersion-corrected GGA PBE method can reproduce the experimental structure, vibrational properties and Raman spectra very well.

Band gap engineering of anatase TiO2 by ambipolar doping: A first principles study

Pure Anatase TiO2 is limited to photocatalytic activity only in the UV region of solar energy, (i.e Eg = 3.2 eV and λ = < 388 nm), which utilizes only 5% of the solar spectrum. Adding external impurities to Anatase TiO2 facilitates absorption of the visible spectrum by reducing the band gap of TiO2. Hence, we investigated the effect of Sc and V mono-doping and co-doping on the pure anatase TiO2 by Density Functional Theory (DFT). To elucidate the effect of doping on the electronic structure, the accurate band structure and density of states are derived using the hybrid functional methodology (HSE06). The defect formation energy of the dopants in their different charge states is calculated using the gradient-corrected density functionals using the PBE method. The bonding characteristics were analyzed using the charge density and electron-localization function (ELF) plots, which indicate that the impurities cause a local lattice distortion, which further influences the band features of TiO2. It is observed that the formation of additional energy states by the external impurities below the conduction band minimum, reduces the band gap of the material significantly. The optical absorption analysis shows that Sc and V co-doping not only improves the absorption in the UV region, but also reaches redshift absorption. Hence the ambipolar co-doping by Sc and V to the pure anatase TiO2 makes it a better for visible light active photocatalyst.

Moderate direct band-gap energies and high carrier mobilities of Janus XWSiP2 (X = S, Se, Te) monolayers via first-principles investigation.

Two-dimensional (2D) Janus materials with extraordinary properties are promising candidates for utilization in advanced technologies. In this study, new 2D Janus XWSiP2 (X = S, Se, Te) monolayers were constructed and their properties were systematically analyzed by using first-principles calculations. All three structures of SWSiP2, SeWSiP2, and TeWSiP2 exhibit high energetic stability for the experimental fabrication with negative and high Ecoh values, the elastic constants obey the criteria of Born-Huang, and no imaginary frequency exists in the phonon dispersion spectra. The calculated results from the PBE and HSE06 approaches reveal that the XWSiP2 are semiconductors with moderate direct band-gaps varying from 1.01 eV to 1.06 eV using the PBE method, and 1.39 eV to 1.44 eV using the HSE06 method. In addition, the electronic band structures of the three monolayers are significantly affected by the applied strains. Interestingly, the transitions from a direct to indirect semiconductor are observed for different biaxial strains εb. The transport parameters including the carrier mobility values along the x direction μx and y direction μy were also calculated to study the transport properties of the XWSiP2. The results indicate that the XWSiP2 monolayers not only have high carrier mobilities but also anisotropy in the transport directions for both holes and electrons. Together with the moderate and tunable energy gaps, the XWSiP2 materials are found to be potential candidates for application in the photonic, photovoltaic, optoelectronic, and electronic fields.

Structural, elastic, electronic and optical properties of double perovskites Ba2NaXO6 (X = Cl, Br, I): First-principles study

The structural, elastic, electronic, and optical properties of double perovskites Ba2NaXO6 (X = Cl, Br, I) were investigated by first-principles calculations. The obtained results show that the three compounds can exist stably in terms of mechanical and dynamical stabilities, and three structures have anisotropy in elastic behavior. In addition, they are all direct bandgap semiconductors, and the corresponding bandgap values are 0.623 (2.4668) eV, 0.6158 (2.3476) eV, and 2.3820 (4.0947) eV from PBE (HSE06) method, respectively. Its internal chemical bonds and electronic information were also analyzed in detail by the electron localization function (ELF). In terms of optical properties, the three materials exhibit strong absorption and photoconductive properties in the UV region. In these three compounds, Ba2NaBrO6 has the preferable photovoltaic performance and conversion efficiency, making it has the potential application of optoelectronic devices in the UV region.

Buckling variation effects on optical and electronic properties of GeP2S nanostructure: a first-principles calculation

In this study, by using the first-principles calculations based on density functional theory (DFT), the electronic aspects of GeP2S monolayer under the effect of buckling variation parameter (μ = 0, 2, 4, 6) are theoretically investigated by the PBE-GGA approximation method, and the obtained results have been compared with previous similar structures. The imaginary part of the dielectric function and absorption spectra is presented for in-plane and out-of-plane polarization of GeP2S monolayer by PBE, HSE06, and TD-HSE06 methods. Also, optical aspects for this 2D nanostructure are presented in out-of-plane polarization under buckling variation conditions up to μ = 6. It was shown that particularly for the range of visible light spectrum its optical behaviors match with its electronic ones. Consequently, the obtained results suggest GeP2S as a suitable material for designing optoelectronic devices.

Spectroscopic features and electronic properties on tetrazole-based energetic cocrystals under external electric field

The optimized geometry, molecular orbitals, electronic properties and spectra wtheere calculated by DFT-B3LYP and PBE0 methods with 6–311 + g(d, p) and def2-TZVP basis sets. The results show that the change of electric field intensity has a great influence on the NH bond in the tetrazole ring skeleton, and it is more easily-broken under negative electric field. When the electric field changes, the NH bond is always the trigger bond. With the increase of external electric field, the energy gaps of 5-(nitrimino)-1H-tetrazole (A) and 1-methyl-5-(nitrimino)-1H-tetrazole (B) gradually become smaller, and chemical reactions are more likely to occur. Infrared and UV–Vis spectra show obvious vibration effects under external electric field, and both structures A and B show different degrees of red-shift or blue-shift. A and B exhibit basically similar properties under electric field, indicating that the hydrogen atoms and methyl groups on the tetrazole ring in the structure have little effect on the cocrystal.