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By means of the study of the first principles within the framework of density functional theory, the inorganic metal halide perovskite CsGeX3 (X = Cl, Br, and I) is thoroughly investigated for its potential application in the field of green energy harvest. The structural, electronic, optical, mechanical, and piezoelectric properties have been calculated. Herein, the computed electronic properties reveal a direct bandgap semiconducting nature with electronic bandgap Eg$_{\text{g}}$ = 2.01, 1.38, and 0.85 eV for X = Cl, Br, and I, respectively. Since the most prominent absorption peak falls within the vis–UV region, this implies that they are the potential candidates for photovoltaic applications. To check and verify the thermal stability, the MD simulation was performed with time steps up to 5 ps. The highest piezoelectric coefficient values are 0.731, 1.829, and 12.48 C m−2 for X = Cl, Br, and I, respectively. The higher piezoelectric responses indicate the signature of the efficient energy materials for energy harvest through electromechanical processes. [ABSTRACT FROM AUTHOR]

Structural, electronic and optical properties of strained CdS monolayer and bilayer structures are studied to examine the possibility of controlling their properties for application in the field of nano-devices. First-principles density functional theory (DFT) calculations are done as implemented in SIESTA code that uses a pseudopotential and a numerical nano-orbital basis set. Exchange correlation energies were described using the general gradient approximation (GGA) in the form of Perdew–Burke–Ernzerhof (PBE) functional. We have found that the electronic band structure of monolayer and bilayer CdS is quite sensitive to biaxial strain, and as a result bandgap energy can be tuned over a wide range with compressive and tensile strains. While both the monolayer and bilayer structures maintain the direct bandgap nature of the relaxed structure even under compressive strain, tensile strain transforms the material into indirect gap semiconductors with degenerate electronic band structure. It is found that effective masses can also be controlled with biaxial strain, and hence carrier mobility can be improved in the process. Our DFT calculations also predict that in addition to tuning the optical absorption, intensity of direct bandgap absorption in these two structures can be enhanced under tensile strain. [ABSTRACT FROM AUTHOR]

Electronic band structures of B- and C-doped ZnO monolayers (ML) at high doping concentration are studied based on spin-polarized plane-wave DFT with Projector Augmented Wave Potentials and Generalized Gradient Approximation. Our results show that both the B- and C-doped structures at 3.13% impurity atom per supercell exhibit half-metallic ferromagnetic behaviour due to the spin-polarized 2p orbitals of the dopant atom, which are localized within the energy gap of the host lattice. A net magnetic moment of 1μB and 2μB are, respectively, found in the B- and C-doped structures mainly due to the partially filled dopant atom 2 p orbitals. Due to ferromagnetic coupling, magnetic moments from the neighbouring Zn atoms and the subsequent O atoms also contribute to the net magnetic moment. At a higher doping concentration of 6.25% impurity atom per supercell, both the materials completely transformed into metal. It is also found that while C doping maintains its ferromagnetic property at this doping concentration, the B-doped ZnO ML becomes antiferromagnetic metal. Our findings would provide valuable theoretical data for material scientists in fabrication of the doped ZnO ML in laboratory [ABSTRACT FROM AUTHOR]

Based on density functional theory (DFT) calculations, the electronic and magnetic properties of Co2YGe Heusler compounds (Y = Sc, Ti, V, Cr, Mn and Fe) were investigated. The density of states (DOS) and band structures were studied to understand their electronic properties. Of the investigated systems, Co2CrGe and Co2MnGe exhibited 100% spin polarisation at the EF. Co2CrGe was the most stable half-metallic ferromagnet (HMF) with a 0.24 eV energy gap at the Fermi level in the spin down channel. The total magnetic moment also increased as Y went from Sc to Fe, i.e., with increasing valence electrons. The calculated magnetic moments for Co2CrGe and Co2MnGe were 3.999 μB and 5.00 μB, respectively. Based on the calculated results, the HMF character was predicted for Co2CrGe and Co2MnGe. [ABSTRACT FROM AUTHOR]