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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]

The Zinc telluride (ZnTe) system presents appealing optoelectronic properties used in radiology as well as in the detection of terahertz radiation (THz). In this work, we report a theoretical investigation of the ground and excited states of ZnTe and its ions ZnTe+ and ZnTe- using different ab inito methods. The potential energy curves (PEC) are computed using the CASSCF/LANL2DZ and MRCI/LANL2DZ methods. These curves allow inferring the different spectroscopic constants such as the internuclear distance (Re), the harmonic vibration frequency (ωe), the rotation constant (Be) and the dissociation energy (De). Our results indicate that the electronic states of ZnTe and its ions converge to several lower dissociation limits. The existence of unstable and crossings states is due to the presence of rotational and spin–orbit interactions. The results obtained are compared to the existing experimental data and have generally shown a reasonable agreement. [ABSTRACT FROM AUTHOR]

The Zinc telluride (ZnTe) system presents appealing optoelectronic properties used in radiology as well as in the detection of terahertz radiation (THz). In this work, we report a theoretical investigation of the ground and excited states of ZnTe and its ions ZnTe+ and ZnTe- using different ab inito methods. The potential energy curves (PEC) are computed using the CASSCF/LANL2DZ and MRCI/LANL2DZ methods. These curves allow inferring the different spectroscopic constants such as the internuclear distance (Re), the harmonic vibration frequency (ωe), the rotation constant (Be) and the dissociation energy (De). Our results indicate that the electronic states of ZnTe and its ions converge to several lower dissociation limits. The existence of unstable and crossings states is due to the presence of rotational and spin–orbit interactions. The results obtained are compared to the existing experimental data and have generally shown a reasonable agreement. [ABSTRACT FROM AUTHOR]

Laser-induced carbon plasma in air undergoes various physicochemical processes that affect the kinetic chemistry of species of the plasma plume. We report the time- and space-resolved characterization of carbon plasma produced by infrared nanosecond laser into air at atmospheric pressure. Investigating the laser fluence effect highlights dissociation for fluences >40 J cm−2, and recombination processes in the fluence range of 10–40 J cm−2. Emission intensities of C2 and CN molecules undergo an enhancement at specific spatiotemporal locations in the laser-induced plasma. At a value of 27 J/cm2 and 0.8 mm from the plasma ignition, molecular band formation is favored for the specific temperature and density values of 1.7 × 1015 cm−3 and 9502 K. The vibrational temperatures of molecules are determined using nonlinear spectral data fitting program. The shock front between laser-induced carbon plasma and air may lead to a significant shock wave that affects the occurrence of molecular CN and C2 formation. This can be explained by the distinct temperatures exhibited by CN and C2 molecules with laser fluence. The atomic carbon travels farther to react and form C2, where the ionization–recombination process plays a significant role in its formation. Collisions of C with N neutrals and N2 molecules are the plausible origin of CN generation. Moreover, the density of CN in the plasma depends on C2 molecules. [ABSTRACT FROM AUTHOR]