Investigations on the structural and optoelectronic characteristics of cadmium-substituted zinc selenide semiconductors.

A change in the composition and dopant content of selective atoms in a material leads to their new desired properties by altering the structure, which can significantly improve the performance of relevant devices. By acknowledging this, we focused on characterizing the optoelectronic and structural properties of cadmium-substituted zinc selenide (Zn1-xCdxSe; 0 ≤ X ≤ 1) semiconductors using density functional theory (DFT) within the generalized gradient approximation (GGA), EV-GGA, and mBJ approximations. The results proved the cubic symmetry of the investigated materials at all Cd concentrations (0, 0.25, 0.50, 0.75, and 1). Although a linear surge in the lattice constant is observed with the change in Cd content, the bulk modulus exhibits a reverse trend. These materials are observed to be direct bandgap semiconductors at all Cd concentrations, with a decrease in electronic bandgap from 2.76 eV to 1.87 eV, and have isotropic optical properties, showing their potential applicability as a blue-to-red display. The fundamental optical properties of the materials, such as optical conductivity, reflectance, refractive index, absorption, and extinction coefficient, are also discussed. These outcomes provide a computational understanding of the diverse applications of Zn1-xCdxSe semiconductors in optoelectronic, photonic, and photovoltaic devices, particularly for a visible-range display.

Beryllium and Magnesium Metal Clusters: New Globally Stable Structures and G0W0 Calculations.

We study the structural and electronic properties of beryllium (Be) and magnesium (Mg) clusters for sizes 2-20 using a two-step approach. In the first step, a global search of the stable and low-lying metastable isomer structures is carried out on the basis of first-principles potential energy surfaces at the level of the generalized gradient approximation (GGA) of density functional theory (DFT). In the second step, vertical ionization potentials (VIPs) and energy gaps between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are determined using the G0W0 methods for up to the fourth-lowest-energy isomers. Novel globally lowest-energy isomer structures are identified for Be14, Mg14, and Mg16 clusters. The van der Waals interactions are found to have a stronger influence on Mg clusters than on Be clusters. A second-difference analysis for both the binding energies and HOMO-LUMO gaps reveals a close relationship between the structural stability and chemical hardness for both types of clusters.