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In this study, we investigated the optoelectronic properties of cubic (Pm3m) and orthorhombic (Pnma) CsPbX3 (X = I, Br, and Cl). We utilized the full potential linear augmented plane wave method, which is implemented in the WIEN2k code, to facilitate the investigation. Different exchange potentials were used to analyze the optoelectronic behavior using the available density functional theory methods. Our findings revealed that CsPbX3 perovskites display direct band gaps at the R and Г points for cubic (Pm3m) and orthorhombic (Pnma) structures, respectively. Among the exchange potentials, the mBJ-GGA method provided the most accurate results. These outcomes concurred with the experimental results. In both Pm3m and Pnma structures, interesting changes were observed when iodide (I) was replaced with bromine (Br) and then chlorine (Cl). The direct band gap at the R and Г points shifted to higher energy levels. Similarly, when I was replaced with Br and Cl, there was a noticeable decrease in the absorption coefficient, dielectric constants, refractive index, and reflectivity, in addition to a band gap shift to higher energy levels. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Structural transformation for wurtzite BeO under in-plane strain at 16.3%. • Electronic band structure has transformed from direct to indirect when applying large strain. • Electronic and optical properties of unstrained and strained BeO were investigated. • A considerable anisotropy between the components was found for strained BeO. Abstract Structural, electronic, and optical properties of wurtzite BeO under biaxial in-plane strain are investigated using first principles calculations. The present calculations are based on all the electrons' Full-Potential Linearized Augmented Plane Wave plus local orbital (FP-LAPW + lo). The planar strain is introduced to investigate the bonding characteristics, electronic properties, and optical properties of BeO. We observe that BeO is more stable in an h-MgO structure under large tensile strains. Structural, electronic, dielectric, and optical properties of strain-free and strained BeO wurtzite crystal are examined. Our results indicate that the biaxial strains change the bond lengths between Be and O, and we observe a strong correlation between the structural changes accompanying biaxial strains with the electronic structure variations of BeO. The variation in planar strains has a significant impact on the band gap of BeO, which could be proposed as potential candidate for optoelectronic applications. [ABSTRACT FROM AUTHOR]

Abstract: Electronic and optical properties of ternary silver palladium oxide (Ag2PdO2) are investigated using density functional theory. Two different possible approximations for the exchange correlation potentials were employed. The X-ray and neutron crystallographic data were optimized by minimization of the forces (1 mRy/a.u.) acting on the atoms. The electronic structure, electron space charge density, chemical bonding and optical dielectric were determined from the relaxed geometry seeking deep insight understanding of this material. Our calculated energy band gap (0.15 eV) shows a good agreement with the experimental value (0.18 eV). [Copyright &y& Elsevier]

Abstract: First-principles density functional theory was used to investigate effects of in-plane strains on the structural, electronic, and optical properties of wurtzite cadmium selenide (CdSe). The results of this work show some interesting properties of this material under finite strains that do not exist in the bulk unstrained regime. The structural deformation produced by increasing the in-plane strain, including the internal parameter u, was examined. The result shows that the structure undergoes a phase transition at a strain of 9.3% due to an extraordinary increase of the internal parameter u. By analyzing the electronic band structure using the modified Becke–Johnson approximation (mBJ), a direct–indirect band gap transition at an in-plane strain of 9.3% was found. Additionally, optical dielectric constants, reflectivity, and refractive index were calculated at different values of the strain. These results indicate that, by controlling the CdSe biaxial in-plane lattice constant (for example, by epitaxial growth on an appropriate substrate), the electronic and optical properties can be tuned for specific device applications. [Copyright &y& Elsevier]

The effect of halide composition on the structural, electronic, and optical properties of CsPb(Br1−xClx)3 perovskite was investigated in this study. When the chloride (Cl) content of x was increased, the unit cell volume decreased with a linear function. Theoretical X-ray diffraction analyses showed that the peak (at 2θ = 30.4°) shifts to a larger angle (at 2θ = 31.9°) when the average fraction of the incorporated Cl increased. The energy bandgap (Eg) was observed to increase with the increase in Cl concentration. For x = 0.00, 0.25, 0.33, 0.50, 0.66, 0.75, and 1.00, the Eg values calculated using the Perdew–Burke–Ernzerhof potential were between 1.53 and 1.93 eV, while those calculated using the modified Becke−Johnson generalized gradient approximation (mBJ–GGA) potential were between 2.23 and 2.90 eV. The Eg calculated using the mBJ–GGA method best matched the experimental values reported. The effective masses decreased with a concentration increase of Cl to 0.33 and then increased with a further increase in the concentration of Cl. Calculated photoabsorption coefficients show a blue shift of absorption at higher Cl content. The calculations indicate that CsPb(Br1−xClx)3 perovskite could be used in optical and optoelectronic devices by partly replacing bromide with chloride. [ABSTRACT FROM AUTHOR]

The structural, electronic, and optical properties of inorganic CsPb(I1−xBrx)3 compounds were investigated using the full-potential linear augmented-plane wave (FP-LAPW) scheme with a generalized gradient approximation (GGA). Perdew–Burke–Ernzerhof generalized gradient approximation (PBE-GGA) and modified Becke–Johnson GGA (mBJ-GGA) potentials were used to study the electronic and optical properties. The band gaps calculated using the mBJ-GGA method gave the best agreement with experimentally reported values. CsPb(I1−xBrx)3 compounds were wide and direct band gap semiconductors, with a band gap located at the M point. The spectral weight (SW) approach was used to unfold the band structure. By substituting iodide with bromide, an increase in the band gap energy (Eg) values of 0.30 and 0.55 eV, using PBE-GGA and mBJ-GGA potentials, respectively, was observed, whereas the optical property parameters, which were also investigated, demonstrated the reverse effect. The high absorption spectra in the ultraviolet−visible energy range demonstrated that CsPb(I1−xBrx)3 perovskite could be used in optical and optoelectronic devices by partly replacing iodide with bromide. [ABSTRACT FROM AUTHOR]

The structural, electronic, and optical features of CsPb(I 1-x Br x) 3 (x = 0, 0.25, 0.50, 0.75, and 1.0) compounds were evaluated using first-principles calculations based on the full-potential linear augmented plane wave (FP-LAPW). The ground-state properties were examined, with a focus on the structural, electronic, and optical properties of the compounds. The structural features were computed using the PBE-GGA potential, revealing that both the lattice constant and bulk modulus varied nonlinearly with respect to the bromide concentration. Theoretical X-ray diffraction analyses revealed peak shifts to larger angles when the average fraction of bromide incorporated increased, indicating shrinkage in the lattice. While the E g values were calculated using the PBE-GGA potential and resulted the 1.45, 1.43, 1.53, 1.50, and 1.77 eV values, the mBJ-GGA potential values resulted the 1.90, 1.81, 2.11, 2.12, and 2.50 eV for CsPbI 3 , CsPbI 2.75 Br 0.25 , CsPbI 1.5 Br 1.5 , CsPbI 0.25 Br 2.75 , and CsPbBr 3 respectively. In addition to that, the E g values of CsPbI 1.5 Br 1.5 which were calculated using other potentials: LDA and PBEsol potentials have resulted the 1.43 and 1.49 eV values, respectively. The E g of CsPb(I 1-x Br x) 3 obtained using mBJ-GGA potential has relatively matched with previously reported experimental values. The calculated effective masses are highly correlated with the energies of E g, the valence-band maximum (VBM), and conduction-band minimum (CBM). We observed that there was an increase, with small bowing parameters (b), in E g value as the Br concentration increases in the CsPb(I 1-x Br x) 3 compounds. The semiconductor characteristic was prominent in the observed band profiles when PBE-GGA and mBJ-GGA potentials were applied. Additionally, the optical properties were examined in details. The calculations indicate that the CsPb(I 1-x Br x) 3 compounds are promising candidates for optoelectronics. Image 1 • The structural, electrical and optical properties of CsPb(I 1-x Br x) 3 were investigated using the PBE-GGA and mBJ-GGA. • An increase in the band gap energy (Eg) values of 0.32 eV (PBE-GGA) and 0.60 eV (mBJ-GGA) when substituting I with Br. • The calculated band gap (Eg) values using the mBJ-GGA were better matched with the experimental values. • The effective masses of electron and hole were calculated using PBE-GGA and mBJ-GGA potentials. • All the optical properties of CsPb(I1-xBrx)3 were investigated using PBE-GGA and mBJ-GGA potentials in details. [ABSTRACT FROM AUTHOR]