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Emergence of inorganic metal halide perovskites as multifunctional optoelectronic materials are due to their exceptional tunability in optoelectronic properties. This study sought to enhance the physical and mechanical properties of lead-free FrGeI3 perovskites by introducing transition metal dopants (Mn, Co, and Ni). First-principle calculations based density functional theory (DFT) have been utilized to illustrate the impact of transition-metal doping on the structural, electronic, and light-matter interaction properties of FrGeI3. The study found that transition metal doping in FrGeI3 perovskites leads to an increase in the electronic bandgap leading to semiconducting behavior after phase stability confirmation. Enhanced optical and mechanical properties suggest wide industrial applications in optoelectronics to biomedical area. This study provides a sound understanding of the underlying mechanisms of transition metal doping in Fr-contained halide perovskites, which could pave the way to the headway of new optoelectronic and biomedical devices based on these materials.

The structural, electrical, optical, and mechanical characteristics of the lead-free halide double perovskites Cs2NaTlX6 X = F, Cl, Br are calculated by utilizing PBE functional within generalized gradient approximation GGA under the context of density functional theory DFT.The structural properties such as lattice parameter, cell volume, total energy, bulk modulus, pressure derivative, and tolerance factor are computed at equilibrium.The electronic density of states reveals the semiconducting nature of the compound and the band structure exhibits the nature of the band gap to be direct.HSE06 functional is introduced to correct the underestimated band gap as obtained in the GGA-PBE functional.The real and imaginary components of the dielectric function, absorption coefficient, energy loss function, reflectivity, refractive index, and extinction coefficient are analyzed and explained by electronic structures.

Inorganic metal-halide cubic perovskite semiconductors have become more popular in industrial applications of photovoltaic and optoelectronic devices. Among various perovskites, lead-free materials are currently most explored due to their non-toxic effect on the environment. In this study, the structural, electronic, optical, and mechanical properties of lead-free cubic perovskite materials FrBX3 (B = Ge, Sn; X = Cl, Br, I) are investigated through first-principles density-functional theory (DFT) calculations. These materials are found to exhibit semiconducting behavior with direct bandgap energy and mechanical phase stability. The observed variation in the bandgap is explained based on the substitutions of cations and anions sitting over B and X-sites of the FrBX3 compounds. The high absorption coefficient, low reflectivity, and high optical conductivity make these materials suitable for photovoltaic and other optoelectronic device applications. It is observed that the material containing Ge (germanium) in the B-site has higher optical absorption and conductivity than Sn containing materials. A systematic analysis of the electronic, optical, and mechanical properties suggests that among all the perovskite materials, FrGeI3 would be a potential candidate for optoelectronic applications. The radioactive element Fr-containing perovskite FrGeI3 may have applications in nuclear medicine and diagnosis such as X-ray imaging technology.

We perform first principles simulations for the structural, elastic and electronic properties of orthorhombic samarium orthoferrite $SmFeO_3$ within the framework of density functional theory. A number of different density functionals, such as local density approximation, generalized gradient approximation, Hubbard interaction modified functional, modified Becke$-$Johnson approximation and Heyd$-$Scuseria$-$Ernzerhof hybrid functional have been used to model the exact electron exchange-correlation. We estimate the energy of the ground state for different magnetic configurations of $SmFeO_3$. The crystal structure of $SmFeO_3$ is characterized in terms of the lattice parameters, atomic positions, relevant ionic radii, bond lengths and bond angles. The stability of the $SmFeO_3$ orthorhombic structure is simulated in terms of its elastic properties. For the electronic structure simulations, we provide estimates based on density functionals with varying degrees of computational complexities in the Jacob's ladder.

We carry out a systematic theoretical investigation of Magneto Crystalline Anisotropy (MCA) of L10 FePt clusters with alternating Fe and Pt planes along the (001) direction. We calculate the structural relaxation and magnetic moment of each cluster by using ab initio spin-polarized density functional theory (DFT), and the MCA with both spin-polarized DFT (including spin-orbit coupling self-consistently) and the torque method. We find that the MCA of any composite structure of a given size is enhanced with respect to that of the same-sized pure Pt or pure Fe cluster as well as to that of any pair of Fe and Pt atoms in bulk L10 FePt. This enhancement results from the hybridization we observe between the 3d orbital of the Fe atoms and the 5d orbital of their Pt neighbors. This hybridization, however, affects the electronic properties of the component atoms in significantly different ways. While it somewhat increases the spin moment of the Fe atoms, it has little effect on their orbital moment; at the same time, it greatly increases both the spin and orbital moment of the Pt atoms. Given the fact that the spin-orbit coupling (SOC) constant of Pt is about 7 times greater than that of Fe, this Fe-induced jump in the orbital moment of the Pt atoms produces the increase in MCA of the composite structures over that of their pure counterparts. That any composite structure exhibits higher MCA than bulk L10 FePt results from the lower coordination of Pt atoms in the cluster, whether Fe or Pt predominates within it. We also find that bipyramidal clusters whose central layer is Pt have higher MCA than their same-sized counterparts whose central layer is Fe. This results from the fact that Pt atoms in such configurations are coordinated with more Fe atoms than in the latter. By thus participating in more instances of hybridization, they contribute higher orbital moments to the overall MCA of the unit.

For reliable and efficient inclusion of electron-electron correlation effects in nanosystems we propose a combined density-functional-theory/nonhomogeneous dynamical-mean-field-theory (DFT + DMFT) approach which employs an approximate Iterative Perturbative Theory (IPT) impurity solver. The validity of the method is demonstrated by successful examination of the size-dependent magnetic properties of iron nanoparticles containing 11-100 atoms. We show that the DFT+ DMFT solution is in very good agreement with experimental data, in particular it does not lead to the overestimation of magnetization that is found with the DFT and DFT+U techniques. More importantly, we demonstrate that DFT+DMFT approach can be used for accurate and realistic description of nanosystems containing about hundred atoms.