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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]

Density functional theory calculations are used for studying the structural and electronic properties of the derivatives of the N3 complex in order to improve their spectral absorption in the visible region for photoelectrochemical applications. The N3 complex is shown to be a good candidate for enhancing the response of the N3 dye to solar light.

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]

The ONIOM method was used to reproduce geometrical parameters, atomic charges, dipole moment for α and β L-Fucopyranose which are biological interest molecules. The results of ONIOM(MP2/HF) and ONIOM(B3LYP/HF) calculations were compared to the values obtained by means of its corresponding theoretical levels MP2, DFT and RHF with 6-31G* bases set, using GAUSSIAN 98 software. [ABSTRACT FROM AUTHOR]

Dipole moments, vibrational and electronic polarizabilities and first hyperpolarizabilities of a set of nine ruthenium (II) complexes, cis-RuL_{2}L'_{2} where L = 2,2'-bipyridine and L' = SCN^{-} (1), SeCN^{-} (2) or TeCN^{-} (3); L = (4,4'-dicarboxyH_{2})-2,2'-bipyridine and L' = SCN^{-} (4), SeCN^{-} (5) or TeCN^{-} (6); L = [(4,4'-dicarboxy)-2,2'-bipyridine]^{-4} and L' = SCN^{-} (7), SeCN^{-} (8) or TeCN^{-} (9) have been evaluated at the non-empirical PBE1PBE/LanL2DZ level. Complete optimizations of their geometrical structures have been made followed by frequency calculations. The order of magnitude and the qualitative variation of μ, Δα^{e} Δα^{v}, Δα^{tot}, β_{vec}^{e}, β_{vec}^{v} and β_{vec}^{tot} in function of the ligands L and L' have also been made. The complexation effects on the vector first hyperpolarizabilities have been studied. The obtained results show that both contributions to β_{vec} are substantially affected by this complexation. The highest effect of complexation is recorded in the case of the complex 8. It has been found that the complexation factor Γ^{e} is less than 0.13 and for all the considered complexes is less than Γ^{v}. The individual normal modes contributions to the vibrational first hyperpolarizability show that only a bit of fundamental normal modes, with frequencies are smaller than 50 cm^{-1}, contribute to more than 10% to &\beta;}^{v}_{vec}. [ABSTRACT FROM AUTHOR]

The two contributions, vibrational and electronic, to the electrical properties polarizability and first hyperpolarizability of monosubstituted acetylene HC≡C—X (with X = F, Cl, Br, OH, SH, BH2, NH2, CH3, and SiH3) have been evaluated using the self-consistent field wave functions within the double-harmonic oscillator approximation. The results show that both contributions to the electrical properties are sensitive to the nature of the substituent: electronegativity, atomic volume, and X-weight. In some cases, X = NH2, SiH3, and SH, the nonlinear optical response is essentially due to, and only to, the vibrational response βνL of the molecule. A complete study is made upon two tracks, upon the intrinsic properties of X and upon the IR and Raman spectra as well as the sum-over-modes expression. We also calculated the electrical properties at the AUG-cc-pVDZ basis set and at geometric parameters optimized at different levels of theory (B3LYP and MP2). © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004 [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]