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Context: The key factor in designing heat-resistant energetic materials is their thermal sensitivity. Further research and prediction of thermal sensitivity remains a great challenge for us. This study is based on first-principles calculations and establishes a theoretical model, which comprehensively considers band gap, density of states, and Young's modulus to obtain a empirical parameter Ψ. A quantitative relationship was established between the new parameter and the thermal decomposition temperature. The value of Ψ is calculated for 10 energetic materials and is found to have a strong correlation with the experimental thermal decomposition temperature. This further proves the reliability of our model. Specifically, the larger the value of Ψ, the higher the thermal decomposition temperature, and the more stable the energetic material will be. Therefore, to some extent, we can use the new parameter Ψ calculated by the model to predict thermal sensitivity. Methods: Based on first-principles, this paper used the Cambridge Serial Total Energy Package (CASTEP) module of Materials Studio (MS) for calculations. The Perdew-Burke-Ernzerhof (PBE) functionals in Generalized Gradient Approximation (GGA) method as well as the Grimme dispersion correction was used in this paper. [ABSTRACT FROM AUTHOR]

Methods: This study used molecular dynamics (MD) to simulate three materials (HMX, FOX-7, and TATB) under the NVT ensemble. Six temperatures (100 K, 200 K, 300 K, 400 K, 500 K, and 600 K) were simulated. In addition, the trigger bond lengths, energy bands, and density of states of three materials were obtained at different temperatures and compared with the calculated results at 0 K. Context: The results indicate that the trigger bond lengths of the three materials are very close to the experimental values. Overall, the maximum and average bond lengths of the trigger bonds increase with increasing temperature. The band gap value decreases with increasing temperature. The changes in trigger bond length and band gap value are consistent with the experimental fact that sensitivity increases with increasing temperature. And Eg > 1 eV is consistently found within the temperature range of 0–600 K, indicating that all three materials are non-metallic compounds. [ABSTRACT FROM AUTHOR]

The vibrational, mechanical, electronic, and optical properties of the ε-O8 phase in the pressure range of 11.4–70 GPa were studied by the first-principle calculation method. The phonon dispersion curves have a tiny virtual frequency at 60 GPa, which indicates that ε-O8 is dynamically unstable at 60 GPa. However, the 3-BM EOS demonstrates that the unit cell is stable up to 70 GPa. It has been shown that ε-O8 remains ductile within the whole applied pressure range. Concurrently, we calculated the variation of the band gap of ε-O8 in the pressure range of 11.4–70 GPa. The results show that the band gap of ε-O8 decreases with increasing pressure. Notably, the band gap disappears within the range of 50–60 GPa, which reveals that the metallic phase transition occurs within this pressure range. [ABSTRACT FROM AUTHOR]

The first-principles calculations with density functional theory were performed to investigate the effects of transition metal elements (Mo, Cu, Fe, Ni and Nb) on the physical properties of the Ti–Al-based compounds. Our optimized crystal parameters are in good agreement with the previous theoretical and experimental values. The mechanical stability is verified by the independent elastic constants. The B/G and Poisson's ratio ν both show that Al6TiMo is brittle, while other compounds exhibit ductility. The values of compression anisotropy of the compounds are small, but the shear anisotropy of AlCu2Ti and AlNi2Ti is much more intense than that of other compounds. The anisotropy in elastic properties of AlFe2Ti and AlNbTi2 is smaller than that of the others. It can be seen that the capacity to compress along c-axis is smaller than that along a-axis and b-axis for AlNbTi2. For AlNbTi2, the anisotropy of the bulk modulus along a-axis relative to b-axis is more insignificant than that along c-axis relative to b-axis. The hardness and Debye temperature verify that AlFe2Ti has the greatest resistance to the plastic deformation and more intense inter-atomic bonding force, respectively. Band structures and DOS are used to investigate the electronic properties. The band structures without band gaps show that these ternary Ti–Al-based compounds are conductors. DOS shows the interactions between elements and gives the bond properties. Density of states and charge density both show the strong covalent properties of AlFe2Ti by the hybridization between Fe-3d and Ti-3d states. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H2O2) is used as a fuel and propellant in fuel cells and rockets due to its prominent oxidizing and combustion properties. In addition, hydrogen peroxide, as the energetic material with the simplest molecular structure, exhibits general detonation performance under external stimulation. Based on the first-principle method, we calculated the two crystal structure, electronic properties related to sensitivity closely, optical properties of pure hydrogen peroxide, and 48wt.% hydrogen peroxide (H6O4) under pressure. We found that the band gaps of H2O2 and H6O4 become larger under pressure and the former is larger than the latter; neither has the tendency of metallization phase change. The added peak II of TDOS from H6O4 compared with H2O2 come from molecular H2O in crystal structure. The pressure-induced peak (peak 2 and peak II of TDOS from H2O2 and H6O4) splitting is caused by changes (stronger) in the intermolecular hydrogen bond environment in the crystal under pressure. The specific macroscopic optical properties have the characteristics of overall blue-shift under pressure, which is due to the blueshift of the conduction band and the increase of the band gap. We hope to provide some reference and guidance for deeper future research. [ABSTRACT FROM AUTHOR]

The band structure, total density of states, and atomic orbit projected density of states analysis were performed to investigate HMX/NMP cocrystal by using the first-principles calculations. Results show that the HMX/NMP cocrystal is equipped with a direct band gap and the interactions between HMX and NMP molecules are rather weak. The O orbits hybridize with H orbits, and the parts of charge transform from H to O atoms by analyzing the DOS. The HMX/NMP cocrystal possesses three types of intermolecular interactions between HMX and NMP; these interactions and the arrangement of two molecules in the structure are the main reasons for the low sensitivity of the cocrystal. The C-H...O type hydrogen bond is the key role in forming the structure, and the strength of the hydrogen bond interaction for C-H...O-N is higher than that of C-H...O-C. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The impact sensitivity to external stimuli is a critical parameter to evaluate and design high-performance energetic materials (EMs). Investigating factors that affect sensitivity and further revealing the sensitivity mechanism are still huge challenges. In the present study, a physical model is established to assess impact sensitivity of 16 energetic compounds based on the energy transfer of carriers using first-principles calculation. The results show that the empirical parameter ψ obtained by considering the band gap, the density of states, and the ability of electronic migration has a remarkable correlation with experimental drop energy E 50. This is in favor of the basic assumption that the energetic material would be less sensitive if the electrons transfer energies quickly to other molecules, making it harder to form a hot spot. [Display omitted] [ABSTRACT FROM AUTHOR]

Due to its p-type conductivity, CuAlO2 has been widely studied. However, the conductivity of p-type CuAlO2 is much lower than that of n-type, which limits its applications. We used the generalized gradient approximation and hybrid functional B3LYP to study the effects of chalcogen substitution on the electronic properties and chemical bondings of delafossite CuAlO2. The calculated results show that the doping of chalcogen (S, Se, and Te) substituting for O is thermodynamically stable. The calculated volumes, bandgaps, and valence-band widths of dopants have been detailedly discussed, indicating that the volumes and valence-band widths are increased, but the bandgaps are decreased. The density of states and charge-density distribution ranges have been analyzed, suggesting that chalcogen substitution is a good way to design new p-type Cu-based TCOs. [ABSTRACT FROM AUTHOR]

Due to its p-type conductivity, CuAlO2 has been widely studied. However, the conductivity of p-type CuAlO2 is much lower than that of n-type, which limits its applications. We used the generalized gradient approximation and hybrid functional B3LYP to study the effects of chalcogen substitution on the electronic properties and chemical bondings of delafossite CuAlO2. The calculated results show that the doping of chalcogen (S, Se, and Te) substituting for O is thermodynamically stable. The calculated volumes, bandgaps, and valence-band widths of dopants have been detailedly discussed, indicating that the volumes and valence-band widths are increased, but the bandgaps are decreased. The density of states and charge-density distribution ranges have been analyzed, suggesting that chalcogen substitution is a good way to design new p-type Cu-based TCOs. [ABSTRACT FROM AUTHOR]

Abstract: Two terminations of the tetragonal SrHfO3 (001) surfaces have been investigated using the first-principles density-functional theory within the localized density approximation. The interplanar distances, rumpling parameters, surface band structures, density of states, charge densities, surface energies and stability of the SrO-termination and HfO2-termination have been calculated and analyzed. Results show that two surfaces have the same relaxation characters. Two surfaces demonstrate the reduction of the band gaps with respect to bulk. The charge density distributions near surface have been shown and discussed. The calculated average surface energy of tetragonal SrHfO3 is 1.451 J/m2. [Copyright &y& Elsevier]

Abstract: Structural, electronic and surface properties of the (001) surface of orthorhombic SrHfO3 have been investigated with both SrO and HfO2 termination using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory. The calculated results show the same changed trend of the interplanar distance of two slabs, the reduced band gaps of two slabs by comparison with those of bulk system, the weakened covalent surface in the HfO2-terminated slab and the weakened ionic surface in the SrO-terminated slab. The calculated surface energies indicate the cleavability of the orthorhombic (001) surface is harder than that of cubic (001) surface. The grand thermodynamic potential shows the SrO-terminated slab is more stable. [Copyright &y& Elsevier]

Abstract: We calculated the structural parameters, elastic, mechanical, electronic and optical properties of 3R- and 2H-CuGaO2 using the first-principles density-functional theory. The results show that the structural parameters of two phases are in good agreement with previous theoretical and experimental data. Two phases are mechanically stable, behave in ductile manner and have indirect band gap. The analyses of electronic structures and charge densities of two phases show mainly covalent nature in Cu–O bonds and coexistence of both ionic and covalent nature in Ga–O bonds. The optical properties are obtained and discussed, including the complex dielectric function, refractive index, extinction coefficient, optical reflectivity, absorption coefficient, energy-loss spectrum and complex conductivity function, which provide useful information for the future applications of CuGaO2. [Copyright &y& Elsevier]

To investigate the dependence of corresponding parameters with pressure, the first-principles calculations were implemented to study the physical and chemical evolutions of DATB. The breakpoint of lattice parameters, bond length and angle, vibrational modes, interaction and band gap is observed at 2 GPa, which is close to the discontinuity observed in the experiment around 5 Gpa. The calculational parameters are consistent with the available data, which verifies the reliability of our calculation. Since the compression, the intermolecular arrangement is more steeper and further causing the breakpoint around 2 GPa, which can be attributed to the variation in the hydorgen bonds structrue and no phase transition observed here. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this article, the properties of Cs2Pb2O3 have been investigated using the first‐principles method. It covers the relevant structural, stability, electronic properties, conductivity, and optical properties. The phonon spectra and elastic properties analysis show the stability of Cs2Pb2O3, band structure, density of states, charge density diagram, and bond populations are analyzed to show the electronic structure of the system more clearly. The calculated results indicate that considering spin‐orbit coupling (SOC) will reduce the band gap. The charge density diagram and bond populations indicate that the Cs–O bond is mainly ionic and the Pb–O bond is mainly covalent and partially ionic. The analysis of optical properties indicates good transparency, and the calculated hole mobility is 10.88 cm2 V−1 s−1, suggesting that it is a promising p‐type conductive oxide. [ABSTRACT FROM AUTHOR]

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.The valence and conduction band edge positions as well as defect levels of pure and X-doped NM [ABSTRACT FROM AUTHOR]

Pressure-induced structural changes of dihydroxylammonium 3,3′-dinitro-5,5′-bis-1,2,4-triazole-1,1′-diolate (MAD-X1), an insensitive energetic ionic salt with high detonation performance, was investigated under simulated conditions (0 to 10 GPa). Using the first-principles density-functional theory, the geometrical structure, intra/intermolecular interactions, electronic properties and Raman spectrum were calculated in detail to elucidate material stability. The anisotropic compressibility in MAD-X1 was revealed by variations of lattice parameters. Furthermore, combining internal hydrogen bonds and geometric parameters of each moiety, we could explain the abrupt changes on lattice constants from two aspects, which demonstrated the contribution of hydrogen bonding to decreasing the material sensitivity. Studies on band gap and partial density of state showed that excessive pressure probably inhibit the electron transfer. Additionally, the simulation of vibrational properties suggested a possible phase transition at 7–8 GPa, implying that MAD-X1 could maintain its stability up to 7 GPa. [ABSTRACT FROM AUTHOR]

• A high p-type conductivity (1.48 × 103 S cm−1) has been achieved in LaCuSTe compound. • Firstly obtain theoretical transport properties of layered oxychalcogenides. • Provide the theoretical effective masses, which supplies a gap in previous studies. The family of layered oxychalcogenides has received extensive attention in the field of optoelectronics due to the wide band gaps and p-type conductivity. Herein, seven La-based copper oxide sulfides are considered to explore their unrevealed optical transparency, transport properties as well as the electrical conductivity using ab initio density functional calculations. The obtained results demonstrate that second gap may lead to degradation of the transparency for p-type semiconductors. Our predicted theoretical carrier effective masses of these compounds are expected to supply a gap in previous investigations. The temperature dependence of transport properties shows that the carrier mobility decreases with the increasing temperature because the phonon scattering is intensified as temperature increases. At room temperature, LaCuSTe exhibits a high hole mobility of 461.00 cm2 v−1 s−1 and a high electrical conductivity of 1.48 × 103 S cm−1 which nearly reaches the conductive ability of typical n-type TCOs, like ZnO:Al, TiO 2 :Nb, SnO 2 :F, and Sn:In 2 O 3 (on the order of 102-104 S cm−1). The fundamental mechanism for the high conductivity of LaCuSTe may lies in the light hole effective masses obtained by the enhanced hybridization between 3p or 5p orbitals of S/Te atoms and the Cu-3d states. LaCuSTe is demonstrated as an intrinsic p-type conductor with a native hole concentration of 2.12 × 1015 n/cm−3 (requiring no external doping). It is probably due to the self-compensation effect of native donor defects in LaCuSTe is weaker than that in conductive oxides. [ABSTRACT FROM AUTHOR]

This article tries to find a method to judge the trigger bond from the sensitivity of energy materials (EMs). The results show that the bandgap judgment cannot be used to determine the trigger bond. At the same time, we find that the rate and magnitude of energy changes can be used to identify the trigger bond of EMs. Finally, we discuss the so-called trigger bond. It is not necessarily the first break, but it is the most critical key to cause the initiation of EMs. We name it as the continuous chemical reaction threshold bond. • The validity of band gap criterion for judging the trigger bond of EMs was explored. • Based on stress theory, a method to judge the chemical reaction threshold bond of EMs was proposed. • The study of chemical bonds in EMs is helpful to the study of the initial reaction mechanism. • The most important significance is to save computing costs. [ABSTRACT FROM AUTHOR]

Transparent conducting materials (TCMs) are widely used in many optoelectronic devices. Transition metal oxides account for a large proportion of transparent conducting materials (TCMs). However, some transition metal oxides with p-type TCMs characteristics usually hold large holes effective mass, the performance is not as good as n-type TCMs. The reason is that the VBM (maximum valence band) of most transition metal oxides is mainly composed of strongly localized O-2p orbitals. Reducing the localization degree of electrons in the VBM is the key to solving the problem. In order to study the modulation effect for the addition of nonmetal constituents with less electronegativity (such as S/Se/Te) on the VBM for transition metal oxides, we perform a systematic theoretical study of 12 kinds of M m X n Y l (M = Ti, Zr, Hf and X, Y= O, S, Se, Te) based on density functional theory (DFT), including the structural, electronic, and optical properties. For the potential TCMs candidates (c-ZrOS, t-ZrOS, c-HfOS) that exhibit excellent conductivity and high transparency, the dynamic stability is studied through phonon spectra. For the transition metal compound with the same symmetry, a convenient method to compare the effective mass of holes and band gap is proposed, that is, a larger electronegativity of the entire compound usually means a larger band gap and effective mass of holes. The effective mass of electrons is primarily determined by the localization of the d-orbital of transition metal, the smaller the electronegativity of transition metals means the smaller effective mass of electrons and larger band gap. [ABSTRACT FROM AUTHOR]

Ternary AⅠBⅢC semiconductors are significant for today's electronic equipment and solar cell applications due to their intriguing properties. In this article, first-principles calculations are employed to comprehensively study the fundamental photovoltaic properties, such as the lattice thermodynamics and phonon stability, band gap, antibonding character of band-edge states, electron and hole effective masses, exciton binding energy and optical absorption coefficient of CuAlX 2 (X ​= ​S, Se and Te) materials. Outcomes demonstrate that CuAlS 2 , CuAlSe 2 and CuAlTe 2 compounds have nice mechanical stability, thermodynamic and phonon stability. Compared with CuAlS 2 and CuAlSe 2 crystals, CuAlTe 2 possesses the more appropriate band gap value, smaller binding energy, higher light absorption and utilization efficiency. Due to their high exciton binding energy and Bohr radius, CuAlS 2 and CuAlSe 2 are limited to solar cell absorber applications. Certainly, other properties of CuAlS 2 do not meet conditions like wide band gap value, heavy carrier effective masses and low absorption coefficient. According to direct photovoltaic functionality screening, we find CuAlTe 2 crystal should be a good photovoltaic absorber. [Display omitted] • The photovoltaic functionalities of tetragonal CuAlX 2 have been calculated for the first time. • CuAlTe 2 crystal is a good photovoltaic absorber based on photovoltaic functionality screening. • Band edges of CuAlX 2 are predominated by antibonding states, attributed to producing shallow levels. [ABSTRACT FROM AUTHOR]

In this paper, crystal structures, effective masses, electronic and optical properties of B 6 Ch (Ch = O, S, Se, Te) are studied within density functional theory (DFT). The band structures show that B 6 O, B 6 S and B 6 Se are semiconductors, while the zero-bandgap B 6 Te displays metallic properties. Moreover, the optical properties involving absorption coefficients, refractive index and extinction coefficients of B 6 Ch are shown and analyzed. The obtained results lead to a conclusion that B 6 Ch results in heavier effective masses and poor transparency. This is explained by the fact that the s orbitals of anion will cause lower dispersion of band edge and influence its positions. • Explore that B 6 O, B 6 S and B 6 Se are p-type TCO while B 6 Te is metal. • Offer evidence that chalcogen substitution narrow the band gaps of B 6 Ch. • Discover the dispersion of the top of the valence band affects its band edge position. [ABSTRACT FROM AUTHOR]

• Hole carrier mobility is controlled by varying the ratio of Ta and Nb elements. • Non (n-1)d10ns2 cations in the VBM will be detrimental to the hole transport. • Sn 2 Ta x Nb 2-x O 7 possesses a tunable band gap by varying the amount of Ta (x = 0–2). Via density functional theory, we considered a new member of p-type transparent conducting oxides (TCOs) family, Sn 2 Ta x Nb 2-x O 7 (x = 0, 0.5, 1, 1.5, 2), to modify the carrier mobility, band gaps, optical properties by Ta5+ substitution at Nb5+ sites. The calculated effective masses indicate that the carrier mobility is expected to be controlled by varying the ratio of Ta and Nb elements in Sn 2 Ta x Nb 2-x O 7 compounds. Nb 4d orbital considerably exists in the valence band maximum (VBM) of Sn 2 Ta x Nb 2-x O 7 (x = 0.5, 1, 1.5), which impedes the overlap between Sn 5s and O 2p orbitals. It offers reliable evidence that non (n-1) d10ns2 cations in the VBM would be detrimental to the hole transport in TCOs. The introduction of Ta 5d orbitals promotes the conduction band edge toward a higher level, thus broadening the band gaps of Sn 2 Ta x Nb 2-x O 7. A structural distortion has been observed when Ta5+ ions replaced Nb5+ sites since the two cations have different bindings with the surrounding oxygen atoms. [ABSTRACT FROM AUTHOR]

Using the first-principles density functional theory, we have studied the structural, excitonic and electronic properties of Nb 2 O 5 with five different crystal structures. In this paper, the structural characteristics of monoclinic, orthorhombic and tetragonal systems have been studied. Different from the classical layered structure, Nb 2 O 5 is a layered shear structure composed of a certain number of NbO 6 octahedrons. Exciton effect plays an important role in the physical process of semiconductor. The absorption and recombination of excitons directly affect the light absorption and luminescence of semiconductors. In order to explore the strength of exciton effect, the binding energy of exciton is calculated. By calculating the exciton binding energies, we found that the exciton binding energy for monoclinic Nb 2 O 5 (the space group is C 2/ c) and orthorhombic Nb 2 O 5 were as high as 69.611 and 75.548 meV. The high exciton binding energy is mainly due to the weak dielectric shielding ability and effective electron hole coulomb interaction. The microcosmic reasons for the difference of exciton binding energies in different crystal structures were analyzed by electrical properties. By analyzing the energy band diagram, it is found that the band gap is closely related to the excitonic binding energy. In general, the position of the atom, the shape of the energy band and the strength of the bond are all factors that contribute to the differences in exciton binding energy. [Display omitted] • The number and arrangement of NbO6 octahedra on the shear plane determine the difference of crystal structures for Nb2O5. • The mechanism of the high exciton binding energy for monoclinic Nb 2 O 5 (C 2/ c) and orthorhombic Nb 2 O 5 was revealed. • The position of atom, shape of energy band and strength of bond act synergistically on the exciton binding energy. [ABSTRACT FROM AUTHOR]

LLM-105 is one of the insensitive high explosives (IHE), and has extensive prospective applications in the military and civilian fields. It is well-known that the theoretical method based on first-principles calculations in energetic compounds properties (sensitivity, detonation) analysis is important for us to comprehensively understand energetic materials. Thus, density functional theory (DFT) is employed to calculate the electronic, vibrational and thermodynamic properties of LLM-105 crystal. The generalized gradient approximation (GGA) with Perdew-Burke-Ernzerhof (PBE) and the Grimme method for DFT-D correction were adopted to describe the exchange–correlation potential and van der Waals interactions. The lattice parameters are in excellent agreement with reported experimental and calculated values. Moreover, the theoretical level (GGA-PBE + G) matches the experimental data batter. Band gap related with sensitivity is 1.301 eV. The electronic DOS and phonon dispersion show that LLM-105 crystal with covalent bonds is dynamically stable. The vibrational modes of bonds and chemical groups are described through symmetry system based on point group C 2h of LLM-105 crystal, which is used to discuss the Infrared and Raman active. The vibrational modes analyses in high frequency region show that two amino groups (NH 2 (1), NH 2 (2)) of molecule are different from each other by comparing the bond length, angle and intramolecular hydrogen-bonds length. The thermodynamic properties such as Helmholtz free energy (F), entropy (S), enthalpy (H), Gibbs free energy (G) and heat capacity (C V) are obtained. The calculated results of several kinds of properties are in agreement with experimental values. We hope providing some reference and guidance for deeper future research. [ABSTRACT FROM AUTHOR]

To study the capacity of materials to degrade organic pollutants, the corresponding key factors for three phases of Ba 2 BiTaO 6 were performed by first-principles calculations. To ensure the accurate description for electronic properties, GGA and HSE06 were employed to do corresponding calculations and the results verify the higher precision of HSE06. Thereby, following properties are all performed by HSE06. It can be noticed that these three phases are mainly utilizing UV light and show the high efficiency in UV region due to the wide band gaps. Monoclinic phase is favorable for forming the photo-generated electron-hole pairs, which can be attributed to the smallest band gap. Compared with TiO 2 and high efficient perovskite photocatalysts, the lower effective masses of electron for these phases suggest the stronger capacity to transfer charge to surface, indicating the higher photocatalytic activity. Therein, monoclinic phase owns the greatest and weakest capacity for carrier transfer and segregation, respectively. Redox potentials show the high efficiency in photocatalytic generation and degrading organic pollutants for these phases and the defect of insufficient utilization of light can be solved by adopting some methods to further promote their photocatalytic applications. Image 1 • Monoclinic Ba 2 BiTaO 6 are easiest to form photocatalytic electron-hole pair. • Ba 2 BiTaO 6 have the high efficiency for transferring charge. • Ba 2 BiTaO 6 have enough capacity to degrade organic pollutants. [ABSTRACT FROM AUTHOR]

First-principles calculations of electrons, phonons and elasticity are used to investigate KH 2 PO 4 based on the density-functional theory. Calculated lattice parameters are in agreement with the available theoretical and exprimental data. Electronic structure reveals that the KH 2 PO 4 has a direct band gap. Calculated phonons show that the vibration of O 1 ...H O 2 causes a LO* split, generating the second harmonics generation (SHG) and double refraction of KH 2 PO 4 because of the depolarization field of vibrational O 1 ...H O 2. Born effective charge proves the existence of depolarization field. Optical properties including the dieletric function, refractive index, extinction coefficient, reflectivity, abosrption coefficient, loss function, and optical conductivity are calculated, revealing that KH 2 PO 4 has a fine transmission and optical anisotropy. Elastic constants, elastic compliance, bulk modulus, shear modulus, Young's modulus, Poisson's ratio, compressibility, Lamé constants, sound velocity and Debye temperature of tetragonal KH 2 PO 4 are calculated to discuss the mechanical perperties. [ABSTRACT FROM AUTHOR]

• There is a good correlation in the N–N average bond population versus bond length. • There is a general upward tendency in excess energy versus N–N average bond length. • Excess energy versus N–N average bond population present an overall downward trend. • The excess energy ε and nitro group charge –Q NO2 have noticeable correlation. • The excess energy is regarded as theoretical criterion of sensitivity for surfaces. The sensitivity of energetic compounds is different from one crystal direction to another, known to be anisotropic. To explore the effects of different surfaces on impact sensitivity, we investigate the structural properties, energies, electronic structure and impact sensitivity of various surfaces of ε-Cl-20 based on the first-principles calculations, the surfaces including (0 0 1), (0 1 0), (0 1 1), (0 1 2), (0 2 1), (1 0 0), (1 0 1), (1 0 2), (1 1 0), (1 1 1), (1 2 0), (2 0 1) and (2 1 0). It turns out that there is a good correlation between the N–N average bond population (Y) versus average bond lengths (X). The (1 0 2) surface has the most extended N–N average bond length, the lowest average bond population, the most substantial excess energy, and lowest nitro group charge, which indicate that (1 0 2) surface has the maximum impact sensitivity compared to other surfaces. There is a clear trend for band gap to decrease as excess energy becomes larger except (1 0 2) and (2 0 1) surfaces. The lower nitro group charge −Q NO2 is, the more massive excess energy is, and the higher impact sensitivity is. The results indicate that the excess energy is regarded as a theoretical criterion of sensitivity to surfaces of ε-Cl-20. [ABSTRACT FROM AUTHOR]

The exploration of relationship between energetic density and stability is essential for the development of high energy density materials. Using the first-principles calculations, we investigate the electronic structures and effective masses of TATB/2D (graphene, MoS 2 , MoTe 2 , WS 2) heterogeneous energetic materials. We find that the main contribution to the band gap decrease is due to the energy bands moving towards lower energy levels. The decreased effective mass with the increasing pressure is the same as the change of band gap, meaning that the decreased effective mass after heterogeneity is good for sensitization of energetic materials. The introduction of 2D materials into insensitive high explosives is a promising way to make controlled explosives. • The effective mass is firstly used to judge the sensitivity. • Introducing 2D materials is a significant way to make controlled explosives. • The decreased effective mass after heterogeneity is good for sensitization of HEDMs. [ABSTRACT FROM AUTHOR]

We perform the first-principles calculation based on density-functional theory (DFT) to study the structural, electronic and mechanical properties of two MgSiO 3 polymorphs (trigonal R‾3 and monoclinic P2 1 /c) under pressure. The optimized lattice parameters of two MgSiO 3 polymorphs under pressure are obtained and analyzed. Comparing the enthalpy values of the two structures under pressure, we find that monoclinic MgSiO 3 will translate into trigonal structure in the range of 10 GPa–20 GPa. The relationship between the band structure and pressure is revealed. And we calculate the total density of state (TDOS) under different pressures and partial density of state (PDOS) under 0 GPa. The electron populations are obtained for trigonal and monoclinic MgSiO 3. We systemically studied the mechanical properties of trigonal and monoclinic MgSiO 3 under pressure including elastic constants, bulk modulus, shear modulus, Lamé's constants, Young's modulus, Poisson's ratio as well as B/G values. According to the modified Born stability conditions under pressure, trigonal MgSiO 3 is stable from 0 GPa to 150 GPa, but monoclinic MgSiO 3 is unstable from 80 GPa to 100 GPa. Image 1 • Discover the transition pressure of monoclinic MgSiO 3 and trigonal MgSiO 3 according to the enthalpy values. • For the first time, offer a comparison of the band gaps of MgSiO 3 under pressure within GGA-PBE and HSE06. • Carry out a study under higher pressure up to 150 GPa for trigonal MgSiO 3 and 100 GPa for monoclinic MgSiO 3. [ABSTRACT FROM AUTHOR]