First-principle calculations were used to investigate the structural, optoelectronic, elastic and thermodynamic properties of Br-doped CsPbI₃ perovskite material using GGA-PBE, SCAN, and LDA functionals. The computed lattice parameters are consistent with the experimental and theoretical calculations, reported in the literature. The band structure along with the electronic density of states indicated that CsPbI_3−xBr_x (x = 0, 1, 2, 3) materials are semiconductors with direct band gaps, as projected using the three functionals. The energy band gap of CsPbI₃ was tuned by replacing I ions with Br ions, resulting in CsPbI₂Br, CsPbBr₂I, and CsPbBr₃ materials. These perovskite materials were found to be mechanically stable, ductile in nature and elastically anisotropic. The results of optical parameters such as absorption coefficients, refractive index, optical conductivity, optical reflectivity, electron energy loss, and extinction coefficients were calculated and analysed. The thermodynamic parameters including heat capacity, and Debye temperature were calculated. The direct band gap and energy-dependent optical parameters especially the absorption coefficient in the infrared and visible region of these perovskite materials suggest that they might be candidates for potential use in photovoltaic solar cells and optoelectronic applications.

The impact of Na atom deintercalation on olivine NaMnPO₄ was investigated in a first-principle study for prospective use as cathode materials in Na-ion batteries. Within the generalized gradient approximation functional with Hubbard (U) correction, we used the plane-wave pseudopotential approach. The calculated equilibrium lattice constants are within 5% of the experimental data. The difference in equilibrium cell volumes for all deintercalated phases was only 6%, showing that NaMPO₄ is structurally more stable. The predicted voltage window was found to be between 3.997 and 3.848 V. The Na₁MnPO₄ and MnPO₄ structures are likely to be semiconductors, but the Na₀.₇₅MnPO₄, Na₀.₅MnPO₄, and Na₀.₂₅MnPO₄ structures are likely to be metallic. Furthermore, all independent elastic constants for Na_xMPO₄ structures were shown to meet the mechanical stability requirement of the orthorhombic lattice system.

Cluster expansion, which is a method that describes the concentration-dependent thermodynamic properties of materials while maintaining density functional theory accuracy, was used to predict new (CsPbI_xBr_1−x) structures. The cluster-expansion method generated 42 new stable (CsPb)_xI_yBr_z (where x = 1 to 3 and y and z = 1 to 8) structures and these were ranked as meta-stable structures based on their enthalpies of formation. Monte Carlo calculations showed that CsPbI_0.5Br_0.5 composition separates into different phases at 300 K, but changes to a homogeneous phase at 700 K, suggesting that a different phase of CsPbI₃ may exist at higher temperatures. Among the 42 predicted structures, randomly selected structures around iodide-rich, 50:50, and bromine-rich sites were studied further by determining their electronic, optical, mechanical, and thermodynamic properties using first-principle density functional theory. The materials possess similar properties as cubic Br-doped CsPbI₃ perovskites. The mechanical properties of these compounds revealed that they are ductile in nature and mechanically stable. This work suggests that the introduction of impurities into CsPbI₃ perovskite materials, as well as compositional engineering, can alter the electronic and optical properties, making them potential candidates for solar cell applications.

Ternary metal dichalcogenide compounds have aroused the interest of the industrial and scientific sectors because of their multiple uses in catalysis, electronics, aerospace, and electrode materials. However, information on the structural and electronic characteristics of XVSe ₂ is still scarce, particularly on the atomic scale. In this study, the first approach principle is used using plane waves to investigate the structural, thermodynamic stability, and mechanical properties of the XVSe ₂ compounds. According to current results, LiVSe ₂ has lower computed lattice parameters than other compounds, and CsVSe ₂ has higher lattice values. The calculated heats of formation showed that the XVSe ₂ compounds are thermodynamically stable due to ΔH _f < 0. The LiVSe ₂ structure was found that the LiVSe ₂ structure had the lowest ΔH _f proving that the Li-type structure is more stable than K, Rb and Cs. In addition, the projected density of states and elastic constants were investigated and discussed. Therefore, XVSe ₂ compounds are found to be mechanically stable.