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.

Structures, cold pressure lines, and electronic properties of cubic Al2O and AlO: First-principles calculations.

Aluminized explosive has attracted more and more attention in recent years because of its high explosive heat and high power. Al2O and AlO are indispensable aluminum oxides in the explosion process of aluminized explosives. The study of the physical properties of solid Al2O and AlO under pressure may play an important role in the understanding of the explosion mechanism of aluminized explosives. CONTEXT: The structures, cold-pressed lines and electronic properties of cubic Al2O and AlO are calculated and analyzed based on first-principles calculation in this paper. The optimized structures of Al2O and AlO are in good agreement with those previously studied. The cold pressure line shows that the specific volumes of Al2O and AlO decrease with increasing pressure. The peak values and peak positions of density of state of Al2O and AlO change greatly under pressure. METHODS: The CASTEP code was used to execute these calculations throughout the present work, where the plane-wave basis set and norm conserving pseudopotential were employed.

Electrons and phonons of the discharge products in the lithium-oxygen and lithium-sulfur batteries from first-principles calculations.

Batteries have become a ubiquitous daily necessity, which are popularly applied to mobile phones and electric vehicles according to their size. Improving the battery cycle life and storage is important, but unexpected discharge products still restrict the upper limit of batter performance such as Li2O2, LiO2, and Li2S. In this study, we calculated electrons and phonons presenting the basic energy states in crystal using the first-principles calculations. The Li2O2 and Li2S are almost insulating due to the wide bandgap from their electronic structure, and doped-active p-orbital may be one of the pathways to improve crystal conduction due to the tendency of the density of states. The LiO2 is metallic, and the electronic structure and phonons show that the discharge products have an ionic feature. In addition, the ionic crystal can produce a larger DC permittivity because it possesses macroscopic polarisation. For Li2O2 and Li2S, the Raman peak of the O-O bonding is strong, while the Raman peak of the S-ion is very weak. The enhanced Raman peak of the S-ion presents a possibility to prevent the shuttle effect in Li-S batteries.

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.

Electronic, optical, and vibrational properties of B3N3H6 from first-principles calculations.

The structural, electronic, optical, and vibrational properties of B3N3H6 have been calculated by means of the first-principles density functional theory (DFT) calculations within the generalized gradient approximation (GGA) and the local density approximation (LDA). The calculated structural parameters of B3N3H6 are in good agreement with experimental data. The obtained band structure of B3N3H6 shows that it has an indirect band gap with 5.007 eV, indicating that it presents insulation characteristic. The total and partial density of states (DOS) of B3N3H6 are given, which tell us the states of the orbital occupation. With the band structure and density of states, we have analyzed the optical properties including the complex dielectric function, refractive index, absorption, conductivity, loss function, and reflectivity. By the contrast, it is found that optical anisotropy is observed in the (001) direction and (100) direction. Moreover, the vibrational properties have been obtained and analyzed, showing that B3N3H6 is dynamically stable due to that there is no imaginary frequency. The frequencies associating with the vibrations are given, which show that B3N3H6 has a low mechanical modulus and thermal conductivity.

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.

The Raman and IR vibration modes of metal pentazolate hydrates [Na(H2O)(N5)]·2H2O and [Mg(H2O)6(N5)2]·4H2O.

The detailed illustrations of the structures, elastic properties, and Raman and IR vibration modes for [Na(H2O)(N5)]·2H2O (a) and [Mg(H2O)6(N5)2]·4H2O (b) have been presented in this investigation by using the first-principles method based on the density functional theory. Our results indicate that the active centers of both two types of the energetic metal pentazolate hydrates appear on the cyclo-N5. The bonding character of N atoms in the cyclo-N5 is shown to be covalent, and the cyclo-N5 ring can be considered as an anion. Based on the analysis of elastic properties, we conclude that complex a is easier to deform than b, and both complexes are mechanically stable. From the calculated Raman and IR vibration modes, the vibration in the region of 960-1206 cm-1 (for a) and 985-1208 cm-1 (for b) is determined by basically mixing the cyclo-N5 stretching and deformation modes. The vibrational modes of a and b in their highest frequency zones are both related to the stretching of the O-H bonds.

Vibrational, thermodynamic, and dielectric properties of ε-CL-20: first-principles calculations.

The DFT theory is used to investigate the vibration forms of ε-CL-20 by discussing the phonon DOS and infrared and Raman spectra. By observing them, the detailed vibration forms can be obtained, and the vibrations are different in the different regions. Our calculated vibrational results are consistent with previous data. In order to deeply comprehend CL-20, we also investigate the thermodynamic properties, finding that entropy, enthalpy, Debye temperature, and heat capacity are increased with the rising temperature and the vibrational free energy decreases with the increasing temperature. The εxx, εyy, and εzz are similar, which reflects the small anisotropy among [100], [010], and [001]. Moreover, it can be noticed that the major contribution for static dielectric constants originates from the electronic contribution.

First-principle calculations of electronic, vibrational, and thermodynamic properties of 1,3-diamino-2,4,6-trinitrobenzene.

Energy-containing materials have aroused people's widespread concern because of its admirable performance in recent years. In this paper, the electronic structure, vibrational, and thermodynamic properties of 1,3-diamino-2,4,6-trinitrobenzene (DATB) are systematically investigated by adopting the first-principle calculations. We find that lattice parameters are in excellent agreement with the previous calculated and experimental values. The vibration spectra are described in detail and the peaks in the Raman and infrared spectra are assigned to different vibration modes. Phonon dispersion curves indicate that the DATB is dynamically stable. According to the vibrational properties, the thermodynamic functions such as enthalpy (H), constant volume heat capacity (CV), Helmholtz free energy (F), Debye temperature (Θ), and entropy (S) are analyzed. No corresponding experimental values have been found so far, and therefore, knowledge of these properties will provide a reference and guidance for the follow-up research.

A systematic study of the surface structures and energetics of CH3NO2 surfaces by first-principles calculations.

Density functional theory (DFT) has been employed within the generalized gradient approximation and Perdew-Burke-Ernzerhof functional (GGA-PBE) to study the structural and electronic properties of nitromethane (NM) surface models. Different surfaces, including (100), (001), (101), (110), and (111), are considered in this work. The corresponding properties of bulk crystal for NM were also calculated to form a contrast to the slab models. Results with anisotropic characteristics of different surfaces have been observed in this study. There was an obviously great anisotropy in electronic parameters, especially the band gaps of different surfaces, indicating the anisotropic impact sensitivity along different directions of NM. The band gap value for (111) surface, 2.687 eV, was smaller than that of other surfaces, showing a higher impact sensitivity for NM. The estimated anisotropy has been revealed in surface energies for different surfaces. Graphical Abstract The valence band minimum (VBM) and conduction band maximum (CBM) of the nitromethane (100), (001), (101), (110) and (111) surface models.

Effects of different dopant elements on structures, electronic properties, and sensitivity characteristics of nitromethane.

In this study, the doped defects in nitromethane crystals were investigated using first-principles calculations for the first time. We introduce dopant atoms in the interstitial sites of the nitromethane lattice, aiming to study the effects of element-doping on the structural properties, electronic properties, and sensitivity characteristics. The obtained results show that doped defects obviously affect the neighboring nitromethane molecules. The modification of electronic properties shows that the band gaps are significantly influenced by doped defects. Partial density of states and population analysis further reveal the mechanism for sensitivity control of nitromethane. It is shown that the new electronic states were introduced in the forbidden bands and the doped defects resulted in charge redistributions in the systems. Graphical abstract The valence and conduction band edge positions as well as defect levels of pure and X-doped NM.