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In this study, we investigate the structural, electronic, dielectric, and dynamical properties of gallium nitride in the hypothetical hexagonal P63/mmc phase through first-principles simulations. Electronic structure calculations show strong hybridization and a relatively small band gap of 1.34 eV. Dielectric property simulation demonstrates higher dielectric constants in the layer direction compared to the out-of-layer direction, attributed to the weaker van der Waals interactions between layers in the hexagonal structure. The Born effective charges suggest a predominantly ionic character in GaN, with significant anisotropy in charge distribution. Phonon band structure analysis reveals the presence of unstable phonon modes at the Γ and A points indicating dynamic instability in this configuration. Phonon band structure analysis reveals the presence of unstable phonon modes at the Γ and A points, indicating dynamic instability in this configuration. This instability can be controlled by applying external parameters, such as pressure, to synthesize GaN in this structure. Moreover, the detailed decomposition of the phonon modes provides insights into the structural instability, emphasizing the role of short-range interactions. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) nanostructures have attracted much interest due to their potential applications in various fields including optoelectronics, glass industries, and solar cells. These compounds hold the promise of creating new materials that can advance energy technologies. In this work, a series of (ZnO)6 clusters with selenium and tellurium applied as substitutional impurities has been studied. The investigated structures have been produced through the doping of (ZnO)6 clusters by replacing an oxygen atom with a selenium or a tellurium atom at each time. The ground state geometric parameters of (ZnO)6 structures, containing selenium or tellurium atoms as substitutional impurities, were calculated using density functional theory (DFT) with B3LYP and LanL2DZ basis set. Excited state energies and absorption wavelengths were computed using time-dependent-DFT (TDDFT). For the calculation of emission wavelengths, Hartree-Fock configuration interaction singles (HF/CIS) has been used in order to perform the excited state geometry optimization. This work led to some important results that can be helpful for developing novel THz sensitive materials and imaging detectors that may be an alternative to x-rays detectors for radiology as well as for the development of solar cells and electroluminescent diodes. Zinc oxide (ZnO) nanostructures have attracted growing interest due to their potential applications in many technological fields, including optoelectronics, the glass industry, and energy. The presence of impurities, in particular selenium and tellurium, in ZnO-based clusters can affect their structural and spectroscopic properties. Some of these doped nanostructures have favorable Terahertz emission characteristics that make them good candidates for applications in biology and medicine. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we present a comparative post-Hartree–Fock and density functional theory study of monochalcogenide diatomic molecules of the XSe and XTe types (where X atom belongs to group 15), including neutral and cationic species. The corresponding bond lengths, vibrational frequencies and ionization potentials are calculated and compared with experimental data or advanced post-Hartree–Fock methods. The choice of the basis sets is also discussed. Finally, dissociation energies of the cationic and neutral species are computed and discussed. [Copyright &y& Elsevier]