Non-toxic lead-free halide metal perovskites have gained significant interest in photovoltaic and optoelectronic device applications.

Perovskite halides are the most promising current candidates for the construction of solar cells and other photovoltaic devices. This is the first theoretical approach to explore the effects of Mn-doping on the optoelectronic performance of the lead-free halide CsGeBr3 and the lead-bearing halide CsPbBr3. We have performed the first-principles calculations to investigate the structural, mechanical, electronic, and optical properties of pure and Mn-doped CsGeBr3 and CsPbBr3 perovskite halides in detail. The lattice constants of Mn-doped halides were slightly reduced compared to their pure phases, which is common in materials after doping. The structural stability of both undoped and doped halides was confirmed by their formation enthalpy. Analysis of the mechanical properties revealed the mechanical stability of both undoped and Mn-doped CsGeBr3 and CsPbBr3. The lower values of the bulk modulus suggested potential optoelectronic applications for the halides being studied. Remarkably, the partial substitution of Ge with Mn narrows the bandgap of both Pb-free and Pb halides, enhancing the electron transfer from the valence band to the conduction band, which increased the absorption and conductivity, essential for superior optoelectronic device applications. The combined analysis of mechanical, electronic, and optical properties indicated that the Mn-doped halides, CsGeBr3 and CsPbBr3, are more suitable for the solar cells and optoelectronic applications than undoped CsGeBr3 and CsPbBr3.

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By using first principles calculation dependent on the density functional theory (DFT), we have investigated the mechanical, structural properties and the Debye temperature of Fe2ScM (M=P and As) compounds under various pressures up to 60 GPa. The optical properties have been investigated under zero pressure. Our calculated optimized structural parameters of both the materials are in good agreement with other theoretical predictions. The calculated elastic constants show that Fe2ScM (M=P and As) compounds are mechanically stable under external pressure below 60 GPa. From the elastic constants, the shear modulus G, the bulk modulus B, Young’s modulus E, anisotropy factor A and Poisson’s ratio [Formula: see text] are calculated by using the Voigt–Reuss–Hill approximation. The Debye temperature and average sound velocities are also investigated from the obtained elastic constants. The detailed analysis of all optical functions reveals that both compounds are good dielectric material.

The relationship between the critical resolved shear stress (CRSS) at T = 0 K and the atomic structure distortion was studied using molecular dynamics (MD) simulation with atomic distortion (root-mean-square-atomic-displacement (RMSAD)) controlled Lennard-Jones (LJ) interatomic potentials for different face-centered-cubic (FCC) high entropy alloy (HEA) systems, such as ternary, quaternary, and quinary alloy systems. We demonstrated that an almost universal linear relationship exists between CRSS and RMSAD for the random solid solution (RSS) of these alloy systems. The universality was also confirmed by a more realistic embedded atom method (EAM) potential. However, alloy systems that have a chemical-short-range-order (CSRO) do not follow this universal linear relationship.

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