We used first-principles calculations to investigate the electrical and optical properties of CsGeX 3 (X = Cl, Br, and I) compounds. These materials present rich and unique physical and chemical phenomena, such as the optimal geometric structure, the electronic band structure, the charge density distribution, and the special van Hove singularities in the electronic density of states. The optical properties cover a slight red shift of the optical gap, corresponding to weak electron–hole interactions, strong absorption coefficients, and weak reflectance spectra. The presented theoretical framework will provide a full understanding of the various phenomena and promising applications for solar cells and other electro-optic materials.

Li2SiO3 compound exhibits unique electronic and optical properties. The state-of-the-art analyses, which based on first-principle calculations, have successfully confirmed the concise physical/chemical picture and the orbital bonding in Li–O and Si–O bonds. Especially, the unusual optical response behavior includes a large red shift of the onset frequency due to the extremely strong excitonic effect, the polarization of optical properties along three-directions, various optical excitations structures and the most prominent plasmon mode in terms of the dielectric functions, energy loss functions, absorption coefficients and reflectance spectra. The close connections of electronic and optical properties can identify a specific orbital hybridization for each distinct excitation channel. The presented theoretical framework will be fully comprehending the diverse phenomena and widen the potential application of other emerging materials.

We investigate the geometric, electric, and optical properties of two-dimensional honeycomb lattices using first-principles simulations.

The three-dimensional ternary LiFeO 2 compound presents various unusual properties. The main features are thoroughly explored by using many-body perturbation theory. The concise physical/chemical picture, the critical spin polarizations, and orbital hybridizations in the Li−O and Fe−O bonds are clearly examined through geometric optimization, quasi-particle energy spectra, spin-polarized density of states, spatial charge densities, spin-density distributions, and strong optical responses. The unusual optical transitions cover various frequency-dependent absorption structures, and the most prominent plasmon modes are identified from the dielectric functions, energy loss functions, reflectance spectra, and absorption coefficients. Optical excitations are anisotropic and strongly affected by excitonic effects. The close combinations of electronic, magnetic, and optical properties allow us to identify the significant spin polarizations and orbital hybridizations for each available excitation channel. The lithium ferrite compound can be used for spintronic and photocatalysis applications.

Solar cell systems are now widely recognized as one of the most impressive structures in engineering applications and basic sciences because they can deliver eco-friendly and renewable energy [1,2] while also being efficient due to the distinct route to convert photon energy into electricity. [1][2][3] Organic-inorganic hybrid perovskite solar cells, [4][5][6][7] specifically ABX 3 (where A represents either cation Cs þ or molecule like CH 3 NH 3 þ , B represents cation Ge 2þ , Sn 2þ , or Pb 2þ , and X indicates anion halogen as Cl À , Br À , I À ) have garnered significant attention for energy harvesting applications due to their exceptional photoelectronic properties. [8,9] However, the presence of lead (Pb) [10,11] in these materials presents safety concerns during synthesis and applications. To reduce toxicity, tin (Sn) is being explored as a potential replacement for lead in the metal halide perovskite structure due to its similar valence electrons for bonding. The orthorhombic phases of CH 3 NH 3 SnI 3 and CH(NH 2 ) 2 SnI 3 perovskites are particularly promising candidates for photovoltaic applications, having attracted a lot of theoretical and experimental investigations. [12][13][14][15] The orthorhombic phases of CH 3 NH 3 SnI 3 and CH(NH 2 ) 2 SnI 3 perovskites have been successfully obtained through various experimental investigations. [15] X-ray diffraction has evaluated the optimal geometric structures of orthorhombic CH(NH 2 ) 2 SnI 3 , [16,17] but no similar measurement has been done for CH 3 NH 3 SnI 3 . Angle-resolved photoemission spectroscopy (ARPES) [18,19] can examine the frequency-dependent energy spectrum at valence states in the electronic band structure, and scanning tunneling spectroscopy (STS) measurement [20,21] allows for identifying the van Hove singularities in both hole and electron states in the density of states (DOS), suggesting the gap value exactly for materials. However, ARPES and STS measurements have not been established in these systems yet. Photoluminescence (PL) measurement [22,23] provides information about the optical properties of a material, including its excitation and emission spectra, which are essential for understanding the efficiency and performance of photovoltaic devices. So far, the PL measurement has been done for the case of orthorhombic CH(NH 2 ) 2 SnI 3 . [15] However, such a measurement has not been reported yet for orthorhombic CH 3 NH 3 SnI 3 .Theoretical calculation utilizing first principles can efficiently predict diverse material properties [5,[24][25][26] and produce accurate results that agree well with experimental measurements. However, the theoretical predictions of the electronic and optical properties of free-lead organic-inorganic perovskite solar cells are still a topic of debate. For instance, Sharma and co-workers [27] used density functional theory (DFT) to predict a direct gap semiconductor of 0.5 eV at the Γ point for the orthorhombic CH 3 NH 3 SnI 3 . In contrast, Feng and Xiao [28] utilized Heyd-Scuseria-Ernzerhof (HSE06) and repo...