The calculated electronic and optical properties of ß-Ga2O3 based on the first principles.

INTRODUCTION: The electronic and optical properties of ß-Ga2O3 have been investigated by CASTEP using first principles. It is found that ß-Ga2O3 has an indirect band gap and the conduction band base is located at the Γ point. The stability of ß-Ga2O3 is demonstrated by the calculation of elastic constants, and the ductility of ß-Ga2O3 is demonstrated by the ratio of Poisson's ratio to shear modulus. The optical property analysis shows that ß-Ga2O3 has a high absorption capacity in the ultraviolet region, but a low absorption capacity in visible and infrared light. CONTEXT: The structure, optical, and electronic properties of ß-Ga2O3 are calculated and analyzed based on first-principles calculation. The optimized structures of ß-Ga2O3 are in good agreement with previously studied. In this paper, the elastic, electronic, and optical properties of ß-Ga2O3 are calculated. METHODS: The CASTEP code was employed to execute these calculations in the present work, where the exchange-correlation interactions were treated in the generalized gradient approximation (GGA) using the Perdew-Burke-Ernzerhof (PBE) functional in the geometry optimizations and electronic and elastic properties.

Study of the relationship between pressure and sensitivity of energetic materials based on first-principles calculation.

CONTEXT: In order to study the relationship between the sensitivity and pressure of energetic materials, six kinds of energetic materials were selected as the research object. The crystal structure, electronic, and phonon properties under hydrostatic pressure of 0 ~ 45 GPa were calculated by first principles. The calculation results show that the lattice parameters and band gap values of these six energetic materials decrease with the increase of pressure. The peak of the density of states decreases and moves to the low energy direction, and the electrons become more active. Meanwhile, the effect of pressure on the sensitivity of the energetic materials is analyzed based on the multi-phonon up-pumping theory. The number of doorway modes and integral of projected phonon density of states under high pressure is calculated. The results show that both of them increase with the increase of pressure. And the smaller the value of the band gap, the larger the number of doorway modes and integral of projected phonon density of states, and the more sensitive the energetic material is. METHODS: All calculations are performed using the Materials Studio software based on density functional theory. The Perdew-Burke-Ernzerhof (PBE) functional of the generalized gradient approximation (GGA) is used to calculate the exchange correlation function, and the Grimme dispersion correction method is used to deal with the weak intermolecular interaction. The structure of the compound was optimized by BFGS algorithm. The linear response is used to calculate the phonon properties of energetic materials. The plane wave cutoff energy was set to 830 eV. The K-point grids of TATB, FOX-7, TNX, RDX, TNT, and HMX were chosen as 2 × 2 × 2, 2 × 2 × 1, 2 × 1 × 1, 1 × 1 × 1, 1 × 2 × 1, and 2 × 1 × 2.

Theoretical study on the correlation between the structure, excess energy, surface energy, electronic structure, nitro charge, and friction sensitivity of N,N'-dinitroethylenediamine (EDNA).

The sensitivity of energetic materials along different crystal directions is not the same and is anisotropic. In order to explore the difference in friction sensitivity of different surfaces, we calculated the structure, excess energy, surface energy, electronic structure, and the nitro group along (1 1 1), (1 1 0), (1 0 1), (0 1 1), (0 0 1), (0 1 0), and (1 0 0) surfaces of EDNA based on density functional theory. The analysis results showed that relative to other surfaces, the (0 0 1) surface has the shortest N-N average bond length, largest N-N average bond population, smallest excess energy and surface energy, widest band gap, and the largest nitro group charge value, which indicates that the (0 0 1) surface has the lowest friction sensitivity compared to other surfaces. Furthermore, the conclusions obtained by analyzing the excess energy are consistent with the results of the N-N bond length and bond population, band gap, and nitro charge. Therefore, we conclude that the friction sensitivity of different surfaces of EDNA can be evaluated using excess energy.

Effects of pressure on structural, electronic, optical, and mechanical properties of nitrogen-rich energetic material: 6-azido-8-nitrotetrazolo[1,5-b]pyridazine-7-amine (3at).

CONTEXT AND RESULTS: 6-Azido-8-nitrotetrazolo[1,5-b]pyridazine-7-amine (3at) is a promising green energetic material, which meets the development requirements of environment-friendly explosives. By discussing the relationship between lattice parameters and pressure, it is found that the compression ratio indicates anisotropy of compressibility. And bond lengths get shorter under pressure, resulting in stronger intermolecular bonds. The N3 group rotates under pressure. And then, the optical properties basically change regularly with the change of pressure. As the pressure increases, the absorption range widens. In the low energy interval, it shows transparency, and then with the increase of energy and pressure, it shows better optical activity. With the increase of pressure and energy, the absorption coefficient increases, representing that the optical activity becomes high. Finally, according to the analysis of mechanical properties, 3at exhibited brittle behavior at 0 GPa and 100 GPa, while at 10 to 90 GPa, the values of ν and B/G are malleable. COMPUTATIONAL AND THEORETICAL TECHNIQUES: Based on density functional theory, the crystal parameters, electronic properties, optical properties, and elastic and mechanical properties of 3at under different pressures were studied theoretically. The GGA-PW91+OBS method was used to calculate the physical parameters under pressure, such as lattice parameters, energy band structures, dielectric function, refractive index, absorption coefficient, and elastic constants. Physical properties under (3at) pressure are predicted.

The effect of pressure on the structural, electronic and vibrational properties of solid carbon dioxide phases.

The structural, electronic and vibrational properties of solid carbon dioxide phases (I, II, III, and IV) under high pressure are studied using first-principles calculations. The calculated structural parameters are in good agreement with the experimental values. The third-order Birch-Murnaghan equation of state is fitted, and the corresponding parameters are obtained. We obtained the phase boundary points of each phase and plotted the phase diagram of solid carbon dioxide. The influence of pressure on the band structure and density of states is studied. The vibrational properties of the four phases of carbon dioxide were studied in detail, and the infrared and Raman spectra of the four phases were obtained. It can be seen from the calculated spectrum that the number and frequency of vibration peaks are in good agreement with the experimental values. And, we also analyze the influence of pressure on the frequency of vibration mode.

First-principles study of the structural phase transition process of solid nitrogen under pressure.

Due to the diversity of solid nitrogen structure, its phase transition has been a hot topic for many scientists. Herein, we first studied the structural softening of rhombohedral solid nitrogen under pressure using first-principles calculations. Then, a new criterion, Egret criterion, was proposed to predict the whole process from beginning to end of structural phase transition of solid nitrogen. Based on the discussion of acoustic phonons, we concluded that the phase transition of rhombohedral solid nitrogen starts from k-point F along the [- 1, - 1, 0] direction in a-axis, and the structural phase transition velocity is slow. Also, we use the Egret criterion proposed by us to predict the emergence of ξ-N2 and the stability of ξ-N2 at 17 GPa and 22 GPa, respectively, and this result is in good agreement with the phase diagram of nitrogen.

First-principles calculation of electronic, vibrational, and thermodynamic properties of triaminoguanidinium nitrate.

In recent years, the important energetic material triaminoguanidinium nitrate (TAGN) has been widely used, and the process of synthesizing TAGN has become more and more perfect. However, there are relatively few theoretical studies on TAGN. This paper uses first-principles calculations to more systematically study the crystal structure, and electronic, vibrational, and thermodynamic properties of TAGN. The calculation results show that the calculated unit cell parameters are relatively consistent with the values obtained through X-ray diffraction experiments. This article describes in detail the state density of the valence electrons of each atom. By analyzing the vibrational properties of TAGN crystal, the vibration mode corresponding to each optical wave is obtained. At the same time, the vibration mode of each peak in the Raman spectrum and the infrared spectrum is described in detail. Then, the calculated value is compared with the experimental value; it can be seen that the error is relatively small. According to the vibration characteristics, a series of thermodynamic functions such as enthalpy (H), Debye temperature (Θ), free energy (F), and entropy (S) are calculated. These thermodynamic functions can provide a certain reference for future research.

Effects of molecular vacancy and ethylenediamine on structural and electronic properties of CH3NO2 surfaces.

The structural and electronic properties of (100) surface for nitromethane (NM) are studied using density functional theory (DFT) with the generalized gradient approximation and Perdew-Burke-Ernzerhof functional (GGA-PBE). Molecular vacancy and ethylenediamine (C2H8N2) substitution are considered in this work. We find that ethylenediamine substitution significantly decreases the band gap, while molecular vacancy increases the band gap slightly. It indicates that ethylenediamine substitution has a positive effect on the impact sensitivity of NM. Also, the formation energies are calculated and the reasons for the decrease of band gap for ethylenediamine substitution and the increase of band gap for CH3NO2 vacancy are explained.