Search

Hexagonal boron nitride (hBN), as one of the few two-dimensional insulators, holds strategic importance for advancing post-silicon electronic devices and circuits. Achieving wafer-scale, high-quality monolayer hBN is essential for its integration into the semiconductor industry. However, the physical mechanisms behind the chemical vapor deposition (CVD) synthesis of hBN are not yet well understood. Investigating morphology engineering is critical for developing scalable synthetic techniques for the large-scale production of high-quality hBN. In this study, we explored the underlying mechanisms of the CVD growth process of hBN and found that the involvement of a small amount of oxygen effectively modulates the shape of the single-crystal hBN islands. By tuning the oxygen content in the CVD system, we synthesized well-aligned hexagonal hBN islands and achieved a continuous, high-quality single-crystal monolayer hBN film through the merging of these hexagonal islands on conventional single-crystal metal-foil substrates. Density functional theory was used to study the edges of hBN monolayers grown in an oxygen-assisted environment, providing insights into the formation mechanism. This study opens new pathways for controlling the island shape of 2D materials and establishes a foundation for the industrial-scale production of high-quality, large-area, single-crystal hBN. The large-scale synthesis of insulating hexagonal boron nitride (hBN) plays an important role for the development of 2D electronics. Here, the authors report the oxygen-assisted chemical vapor deposition of wafer-scale single-crystal monolayer hBN films by merging aligned hexagonal hBN islands. [ABSTRACT FROM AUTHOR]

Context and results: The structure, mechanical, electronic, vibration, and hydrogen bonding properties of a novel high-energy and low-sensitivity 5, 5′-dinitroamino-3, 3′-azo-oxadiazole 4, 7-diaminopyridazino [4, 5-c] furoxan salt have been studied by density functional theory. The calculated vibrational properties show that the low-frequency mode is mainly contributed by the vibration of the -NO2 group, and the high-frequency mode is mainly contributed by the vibration of the -NH2 group and the N7-H3 bond which protonates the cation. In addition, it is analyzed that the first bond to break may be the N-NO2 bond. The calculated hydrogen bond properties indicate that the hydrogen bond between water molecules and cations is N7-H3... O5 (1.563 Å), which is the shortest hydrogen bond among all hydrogen bonds. The presence of this exceptionally short hydrogen bond renders the N7-H3 and H6-O5 bonds resistant to disruption at high frequencies, underscoring the pivotal role of hydrogen bonding in stabilizing the structure of energetic materials. Given the absence of experimental and theoretical data on the electronic, mechanical, and vibrational properties of the material thus far, our calculations offer valuable theoretical insights into the ionic salts of high energy and low sensitivity. Computational methods: All calculations have been carried out based on density functional theory (DFT) and implemented in the CASTEP code. The mode-conserving pseudopotential is utilized to describe the plane wave expansion function, while the PBE functional within the generalized gradient approximation (GGA) is employed to characterize the exchange–correlation interaction. Additionally, dispersion correction is applied using Grimme's DFT-D method. [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]

This study presents a comprehensive analysis of the orthorhombic CsCuO, focusing on its structural, electronic, mechanical, and optical properties, which uses the first‐principles plane wave pseudopotential technique and local density approximation methods based on density functional theory. The derived structural parameters closely match the previously reported experimental data. The calculated results show that CsCuO is mechanically stable and exhibits a certain toughness. Research on electronic properties shows that CsCuO is a direct‐bandgap semiconductor. Charge density and population analysis show that covalent bonds are formed between O and Cu. The optical property results show that CsCuO has good passability to incident light, indicating that CsCuO is an excellent transparent material. In the visible and infrared light regions, CsCuO has a low absorption coefficient, mainly manifested as ultraviolet absorption. Reflection is mainly distributed in the high‐energy region and does not exceed 25% in the visible light region. It can be used in fields that require less light reflection and the manufacture of medical ultraviolet disinfection equipment. [ABSTRACT FROM AUTHOR]

The first‐principles computational methods based on density functional theory are used to study B6O, including its structural, elastic, electronic, and optical properties. The results show that the obtained structural and mechanical parameters are in good agreement with the experimental values. The elastic constants, bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and mechanical stability of rhombohedral B6O are studied. The results show that B6O has mechanical stability, anisotropy, and brittleness. The electronic structure of B6O is analyzed by band structure and density of states. Besides, the chemical bond is systematically explained in terms of Mulliken population and charge density. Finally, the optical characteristics of B6O are examined, encompassing aspects such as the complex dielectric function, conductivity, reflectivity, refractive index, absorption spectrum, and loss function. [ABSTRACT FROM AUTHOR]

Context and results : In this paper, the crystal structure, electronic, optical, and mechanical properties of SrVO3 have been systematically studied by first-principles calculation. The results show that the calculated lattice parameters are in good agreement with the experimental values of X-ray diffraction. The density of states is described in detail in this paper. By analyzing the crystal structure and electronic properties of SrVO3, the magnetic properties of SrVO3 are obtained from the one unpaired electrons of V and the exchange interaction between two V ions. At the same time, a detailed analysis of the optical properties of SrVO3 was conducted, and it was found that it is transparent in the visible light range. Finally, the mechanical properties of SrVO3 are calculated, which can provide some references for future research. Computational method: In this paper, a first-principles method based on density functional theory (DFT) is reported for PBE-GGA analysis using the plane wave-pseudo potential method in a quantum concentrate packet, U value of 7 eV to V-d and a U value of 2 eV to O-p, Grimme correction by DFT-D method. The k points in the Brillouin region are set to 4 × 4 × 4. The energy convergence criterion for self-consistent field calculation is set at 5.0 × 10−6 eV/atom, and the cutoff energy is 1170 eV. In this paper, the force acting on each atom is not more than 0.01 eV/Å, the maximum stress is not more than 0.02GPa, and the maximum atomic displacement is 5 × 10−4 Å. [ABSTRACT FROM AUTHOR]

The structural and electronic properties of perfect and defective MoS have been calculated with first-principles density functional theory. The defect stability has been evaluated using the defect formation energy. The calculated results show that the formation of Mo, S, and Mo–S defects requires extra energy. Moreover, the S vacancy is energetically more favourable than the Mo vacancy. After doping, the defect level is introduced into the forbidden band. The defect level in the Mo defect model tends to be the acceptor level, while the defect level in the S defect model and Mo–S defect model tends to be the donor level. These three different defect models still maintain the direct band gap characteristics as perfect models. Then, the type of conduction after doping is also analyzed. The projected state density and the charge density of these four models have been analyzed, showing the positions of defect energy levels and change of chemical bonds. [ABSTRACT FROM AUTHOR]

Context: The addition of central metal atoms to hydrogen clathrate structures is thought to provide a certain amount of "internal chemical pressure" to offset some of the external physical pressure required for compound stability. The size and valence of the central atoms significantly affect the minimum pressure required for the stabilization of hydrogen-rich compounds and their superconducting transition temperature. In recent years, many studies have calculated the minimum stable pressure and superconducting transition temperature of compounds with H24, H29, and H32 hydrogen clathrates, with centrally occupied metal atoms. In order to investigate the stability and physical properties of compounds with H cages in which the central atoms change in the same third group B, herein, based on first-principles calculations, we systematically investigated the lattice parameters, crystal volume, band structures, density of states, Mulliken analysis, charge density, charge density difference, and electronic localization function in I m 3 ¯ m -MH6 and P63/mmc-MH9 systems with different centered rare earth atoms M (M = Sc, Y, La) under a series of pressures. We find that for MH9, the pressure mainly changes the crystal lattice parameters along the c-axis, and the contributions of the different H atoms in MH9 to the Fermi level are H3 > H1 > H2. The density of states at the Fermi level of MH6 is mainly provided by H 1 s. Moreover, the size of the central atom M is particularly important for the stability of the crystal. By observing a series of properties of the structures with H24 and H29 cages wrapping the same family of central atoms under a series of pressures, our theoretical study is helpful for further understanding the formation mechanism of high-temperature superconductors and provides a reference for future research and design of high-temperature superconductors. Methods: The first principles based on the density functional theory and density functional perturbation theory were employed to execute all calculations by using the CASTEP code in this work. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Context: To find the potential value of Ca3N2 in the field of optoelectronics, the physical properties of Ca3N2 will be analyzed. It can be concluded from the electronic properties that the Ca-N bonds of α-Ca3N2 are more stable than those of δ-Ca3N2 and ε-Ca3N2. The dielectric function, reflectivity function, and absorption function of three types of Ca3N2 were accurately calculated, and it was concluded that α-Ca3N2, δ-Ca3N2, and ε-Ca3N2 have greater transmittance for visible light and exhibit optical transparency in the near-infrared frequency domain. Combined with the high hardness, strong bonding, high melting point, and wear resistance of Ca3N2, Ca3N2 can be used as a new generation of window heat-resistant materials. The α-Ca3N2, δ-Ca3N2, and ε-Ca3N2 are indirect, direct, and indirect narrow bandgap compounds, respectively, that is, δ-Ca3N2 is more suitable for luminescent materials than α-Ca3N2 and ε-Ca3N2. α-Ca3N2 and δ-Ca3N2 have high reflective properties in the ultraviolet region and can be used as UV protective coatings. All three Ca3N2 materials can be used industrially to synthesize photovoltaic devices that operate in the ultraviolet region. Methods: Based on the first-principles of density functional theory calculations, the structures, electronic properties, and optical properties of α-Ca3N2, δ-Ca3N2, and ε-Ca3N2 were calculated. The calculation results show that although the α-Ca3N2, δ-Ca3N2, and ε-Ca3N2 have similar electronic structures, some phases have better properties in some aspects. [ABSTRACT FROM AUTHOR]

Context: 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is a typical insensitive energetic material. It can be used in explosive formulations, such as PBX-9502 and LX-17-0. TATB is an intriguing and unusual explosive for another reason: it crystallizes into a wide array of planar hydrogen bonds, forming a graphite-like layered structure. Therefore, TATB is one of the important research objects, and its surface structure needs to be deeply understood. In this research work, the electronic and energetic properties of TATB (001) surface are explored. Methods: In this paper, the structural, electronic, energetic properties and impact sensitivity of TATB (001) surface structure at 0 and −3 GPa along with x-axis were calculated in this study using the first-principles calculations. The calculations in this paper are performed in the CASTEP code, which is based on the density functional theory with the first-principles calculation method using the plan-wave pseudopotential approach. The exchange-correlation interaction was adopted by the generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) functional. The DFT-D method with the Grimme correction accurately models van der Waals interactions. To model the surface structures of TATB, the planar slab method was employed. We constructed TATB (001) periodic slabs including three layers with a 15-Å vacuum layer. [ABSTRACT FROM AUTHOR]

Using the metal–organic chemical vapor deposition technique, we synthesized a bilayer lateral heterostucture of MoS2 and WS2, each of which layers consist of alternately arranged nanostrips of MoS2 and WS2. Transmission electron microscope images exhibit a checked pattern contrast, reflecting the three distinct interlayer metal arrangements of Mo/Mo, W/Mo (Mo/W), and W/W stacking. Theoretical calculations based on the density functional theory elucidated that the bilayer lateral heterostructure of MoS2 and WS2 exhibits complexed type-II band edge alignments depending on the interlayer metal arrangement: The conduction band edge is located at the Mo atom in a Mo/Mo sector, while the valence band edge is located at the W atom in a W/W sector. According to the complexed band edge alignment, the field-induced carrier injection behavior in the bilayer heterosheet composed of MoS2 and WS2 strips shows gate-induced trans-dimensionality, where the accumulated carrier distributions continuously vary from zero- to two-dimensional based on the applied gate voltage. Tunable carrier dimensionality can be applicable for wide areas of electronics, such as quantum dot arrays with tunable dot–dot interaction. [ABSTRACT FROM AUTHOR]

Context: Based on the first-principles calculations, this paper investigates the structural, elastic, electronic, and optical properties of albite and kaolinite, respectively. It is determined that both of them show structural stability, mechanical stability, and brittleness by calculating formation enthalpy, phonon dispersion, elastic, and mechanically relevant properties. Both materials are insulators with an indirect bandgap. By calculating the TDOS and PDOS, the main characteristics of the electronic structure of NaAlSi3O8 come from O-2p and Si-3p states, O-2p, and Al-3p states hybridization, similar to Al4[Si4O10](OH)8. The covalence of Si–O bonds in NaAlSi3O8 is greater than Al–O bonds, and the covalent property sequence of Si–O bands in NaAlSi3O8 is Si2-O3 > Si1-O4 > Si2-O2 > Si1-O8 > Si1-O6 > Si3-O2 > Si3-O4. The optical anisotropy of NaAlSi3O8 and Al4[Si4O10](OH)8 is analyzed. Methods: First-principles density functional theory (DFT) calculation was carried out by the CASTEP computer program. The GGA-PW91 exchange–correlation was used. The energy convergence tolerance, the maximum force, and the maximum displacement were set in the calculation. [ABSTRACT FROM AUTHOR]

The Hohenberg–Kohn (HK) theorem for interacting electrons is a cornerstone of modern electronic structure calculations. For a general quantum system, a HK‐type Hamiltonian in the form of Ĥhk{gi}=Ĥint+∑igiÔi$\hat {H}_{\rm hk}\lbrace g_i\rbrace =\hat {H}_{\rm int}+\sum_i g_i \hat O_i$ can always be defined, by grouping those terms with fixed or preknown coefficients into an internal part of the Hamiltonian Ĥint$\hat {H}_{\rm int}$, and factorizing the remaining as the superposition of a set of Hermitian operators {Ôi}$\lbrace\hat {O}_i\rbrace$. It is asked whether the HK theorem can be extended to such a general setting, so that the ground‐state expectation values of {Ôi}$\lbrace\hat {O}_i\rbrace$ as the generalized density can in principle be used as the fundamental variables determining all the properties of the system. It is shown that the question can be addressed by the invertibility of generalized density correlation matrix (GDCM) defined with respect to the {Ôi}$\lbrace\hat {O}_i\rbrace$ operators. This criterion is applied to several representative examples, including the quantum Ising dimer, frustration‐free systems, N‐level quantum systems and a fermionic Hubbard chain. It is suggested that for a finite‐size system, finding an invertible GDCM under one single {gi}$\lbrace g_i\rbrace$ configuration is typically sufficient to establish the generic extensibility of the HK theorem in the entire parameter space. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) semiconductors, especially transition metal dichalcogenides (TMDs), have been envisioned as promising candidates in extending Moore's law. To achieve this, the controllable growth of wafer-scale TMDs single crystals or periodic single-crystal patterns are fundamental issues. Herein, we present a universal route for synthesizing arrays of unidirectionally orientated monolayer TMDs ribbons (e.g., MoS2, WS2, MoSe2, WSe2, MoSxSe2-x), by using the step edges of high-miller-index Au facets as templates. Density functional theory calculations regarding the growth kinetics of specific edges have been performed to reveal the morphological transition from triangular domains to patterned ribbons. More intriguingly, we find that, the uniformly aligned TMDs ribbons can merge into single-crystal films through a one-dimensional edge epitaxial growth mode. This work hereby puts forward an alternative pathway for the direct synthesis of inch-scale uniform monolayer TMDs single-crystals or patterned ribbons, which should promote their applications as channel materials in high-performance electronics or other fields. Here, the authors report the direct growth of periodic arrays of 2D semiconductor ribbons by exploiting the step edges of high-miller-index Au facets, showing potential for 2D electronic devices. The synthesized ribbons could also be merged to obtain wafer-scale single-crystal monolayers. [ABSTRACT FROM AUTHOR]

The electrochemical nitrate reduction reaction (NITRR) provides a promising solution for restoring the imbalance in the global nitrogen cycle while enabling a sustainable and decentralized route to source ammonia. Here, we demonstrate a novel electrocatalyst for NITRR consisting of Rh clusters and single‐atoms dispersed onto Cu nanowires (NWs), which delivers a partial current density of 162 mA cm−2 for NH3 production and a Faradaic efficiency (FE) of 93 % at −0.2 V vs. RHE. The highest ammonia yield rate reached a record value of 1.27 mmol h−1 cm−2. Detailed investigations by electron paramagnetic resonance, in situ infrared spectroscopy, differential electrochemical mass spectrometry and density functional theory modeling suggest that the high activity originates from the synergistic catalytic cooperation between Rh and Cu sites, whereby adsorbed hydrogen on Rh site transfers to vicinal *NO intermediate species adsorbed on Cu promoting the hydrogenation and ammonia formation. [ABSTRACT FROM AUTHOR]

Using density functional theory calculations, the structural, electronic, and absorption properties of the promising nitrogen‐rich energetic compound bis‐triaminoguanidinium azotetrazolate (TAGzT) under hydrostatic compression of 0–50 GPa are investigated. The results show that TAGzT has a structural transition at the pressure of 29.4 GPa. The results also show that the compressibility of TAGzT is anisotropic, and its structure is much stiffer in the b direction. Analysis of electronic properties shows that TAGzT transforms into a metallic system at 29.4 GPa due to the structural transition, where TAGzT becomes more sensitive under the pressure compression. The absorption spectra indicate that TAGzT has higher transparency in the infrared region and high optical activity in UV light, and its optical activity increases as pressure increases. This study may provide useful information for understanding how TAGzT behaves under high pressure. [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]

Electronic nematicity is an important order in most iron-based superconductors, and FeSe represents a special example, in which nematicity disentangles from spin ordering. A first-principle description of this order remains elusive. Here, we show that by carefully searching the paramagnetic energy landscape within the density functional theory, a nematic solution stands out at either the +U or hybrid functional level with the lowest energy. The band structure and Fermi surface can be well compared with the recent experimental results. Symmetry analysis assigns the dominant order parameter to the Eu irreducible representations of the D4h point group. Distinct from the B1g Ising nematicity as widely discussed in the context of vestigial stripe antiferromagnetic order, the two-component Eu vector order features mixing of the Fe d-orbitals and inversion symmetry breaking, which lead to striking experimental consequences, e.g., missing of an electron pocket. [ABSTRACT FROM AUTHOR]

The first-principles calculations based on density functional theory are used to obtain structural, mechanical, and electronic properties of Zr–Te compounds. The optimized structural parameters are consistent with the available experimental data. The calculated mechanical properties and formation energy show that the Zr–Te compounds are all mechanically and thermodynamically stable. The bulk modulus B, shear modulus G, Young's modulus E, Debye temperature ΘD, and sound velocity vm are listed, which are positively correlated with the increasing of atomic fraction of Zr. The behaviors of density of states of Zr–Te compounds are obtained. Furthermore, the electronic properties are discussed to clarify the bonding characteristics of compounds. The electronic characteristics demonstrate that the Zr–Te systems with different phases are both covalent and metallic. [ABSTRACT FROM AUTHOR]

The strategy of inducing interlayer anionic ligands in 2D MoS1.5Se0.5 nanosheets is employed to consolidate the interlayer band gap and optimize the electronic structure for the potassium ion battery. It combines complementary advantages from two kinds of anionic ligands with high conductivity and good affinity with potassium ions. The potassium ion diffusion rate is accelerated as well by an optimized lower energy barrier for ion diffusion pathways, with the formation of highly reversible KMo3Se3 crystal other than K0.4MoS2/K2MoS4, which encounters a much slower electro/ion diffusion rate upon discharging. These advances deliver enhanced potassium storage properties with excellent cycling stability, with retained specific capacity of 531.6 mAh g−1 at a current density of 200 mA g−1 even after 1000 cycles, and high rate capability with specific capacity of 270.1 mAh g−1 at 5 A g−1. The insertion and conversion mechanism are also elucidated by a combination of density functional theory computations and in situ synchrotron measurements. [ABSTRACT FROM AUTHOR]

In this paper, the structural, electronic, elastic, mechanical and optical properties of monoclinic Hf 4 CuSi 4 are studied using the first-principles density functional theory (DFT). The calculated structural parameters are consistent with the experimental data. The elastic constants of Hf 4 CuSi 4 structures are calculated, indicating that Hf 4 CuSi 4 shows mechanical stability and elastic anisotropy. According to the B / G and Poisson's ratio, monoclinic Hf 4 CuSi 4 shows a brittle manner. The energy band structure, density of states, charge transfers and bond populations are given. And the band structure shows that the material is a metal conductor. Moreover, the optical properties and optical anisotropy of Hf 4 CuSi 4 are shown and analyzed. [ABSTRACT FROM AUTHOR]

The structural parameters, density of states, electronic band structure, charge density, and optical properties of orthorhombic SrBiTaO have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principle density functional theory (DFT). The calculated structural parameters were in agreement with the previous theoretical and experimental data. The band structure showed an indirect (S to Γ) band gap with 2.071 eV. The chemical bonding along with population analysis has been studied. The complex dielectric function, refractive index, and extinction coefficient were calculated to understand the optical properties of this compound, which showed an optical anisotropy in the components of polarization directions (100), (010), and (001). [ABSTRACT FROM AUTHOR]

[Display omitted] • A porous carbon catalyst containing metallic Co and MgO was successfully synthesized. • Co 1 (MgO) 1 /C exhibited a high oxygen vacancy concentration (O V /O L = 7.77, O V = 51.3%). • Co 1 (MgO) 1 /C - PMS system had high MNZ degradation efficiency. • The MNZ degradation was dominated by 1O 2 via O V regulating directional. In this study, a porous carbon catalyst (Co 1 (MgO) 1 /C) derived from the idea of "reducing metal element/irreducible oxides" was successfully synthesized, characterized and used to activate PMS for removing metronidazole (MNZ) from water. The Co 1 (MgO) 1 /C presented excellent catalytic performances on PMS activation for MNZ removal in a wide pH range and complex water environments. Various advanced characterization technologies and density functional theory (DFT) calculations indicated that Co 1 (MgO) 1 /C possessed a high concentration of oxygen vacancies (O V) (O V = 51.3%), which successfully induced the triple degradation pathway of MNZ in the Co 1 (MgO) 1 /C-PMS systems. Further analysis revealed that the triple MNZ degradation pathway was dominated by singlet oxygen, and supplemented by sulfate radical and electron transfer. Consequently, this study not only expands the existing synthesis methods for high-concentration O V materials but also provides new insights into the directional regulation of non-radical degradation pathways of pollutants. [ABSTRACT FROM AUTHOR]

Dispersion corrected density functional theory (DFT-D) calculation was performed to examine the structural response of 1,3-Diamino-2,4,6-trinitrobenzene (DATB) in the pressure range of 0–15 GPa. The calculated results of the crystal structure, molecular geometry and intermolecular close contacts were in good agreement with the experimental data at ambient pressure. To get further insight into the structural response to pressure of DATB, Hirshfeld surfaces analysis was carried out to elucidate the varied crystal environments. The considerable changes in the pressure dependence of the geometry and various intermolecular close contacts suggested a phase transition occurring around 6.5 GPa. Furthermore, the current study indicated that the Hirshfeld surfaces analysis provided a visual motif for understanding the pressure effect on the energetic molecular crystal DATB. [ABSTRACT FROM AUTHOR]

We have investigated the structural, electronic, magnetic properties and chemical bonding of N-doped rutile TiO 2 by a first-principles ultrasoft pseudopotential of the plane-wave within the density-functional theory (DFT). We find the polarized holes above the Fermi level by 1.058 eV, indicating that the magnetic coupling is mediated by the deep hole doping. The asymmetrical spin of N-2p states are mainly responsible for the origin of the ferromagnetism. The polarized holes from the N 2p π and the Ti 3d (E g +B 2g ) in D 4 h induce the π bonding. [ABSTRACT FROM AUTHOR]

The dispersion corrected density functional theory (DFT-D) calculations were performed to study the structural and vibrational properties of solid nitrobenzene at ambient pressure. Assignments of the calculated vibrational modes were provided. Moreover, using the norm-conserving pseudopotential plus GGA-PBE function, the unit cell parameters, geometries and vibrational frequencies of nitrobenzene were examined under hydrostatic pressure from 0 to 10 GPa. The calculated pressure dependence of lattice parameters and volume were found to be close to the experimental results, but a distinct change in the bond lengths and bond angles was found around 7 GPa. According to the phonon calculations, the pressure-induced changes of the vibrational frequencies were also observed around 7 GPa. These calculated results all suggest a possible structural transformation in the crystalline nitrobenzene. [ABSTRACT FROM AUTHOR]

The conjugate addition reaction of dimethyl propanedioate to 1-nitroprop-1-ene catalyzed by cinchona alkaloid derivatives (QD-R″) is investigated using density functional theory calculations in this paper. The geometry optimizations and frequency calculations were carried out at the B3LYP/6-31G( d, p) level, and the accurate energetic parameters were obtained by the B3LYP/6-311++G(2 df,2 p) method. Our calculations find that cinchona alkaloids with -NCONHPh and -NH electron-withdrawing substituents in the quinuclidine show stronger activation on the system than that with -CH electron-donating substituent. The NBO charge analysis for the tertiary amine nitrogen of the quinuclidine affirms that the electron-withdrawing substituents decrease the negative charges on the tertiary amine nitrogen atom, which is favorable for the second proton transfer from the catalyst to α-carbon of 1-nitroprop-1-ene. As a result, the calculations show that the charge distribution of the tertiary amine nitrogen affects the catalytic efficiency of the system. Furthermore, a detailed analysis of the effects of the solvent on the system further revealed the regularity. [ABSTRACT FROM AUTHOR]

Influences of temperature on thermal properties of monolayer MoS 2 were investigated using first-principles calculations based on the density-functional perturbation theory. The calculated equilibrium vibration properties and Grüneisen parameters γ of monolayer MoS 2 are in good agreement with the available experimental and theoretical values. Interestingly, γ of acoustic modes show an evidently asymmetric character due to the sandwiched structure of monolayer MoS 2 while γ of optical modes display an approximate symmetry in the first Brillouin zone. Thermal properties analysis shows that temperature has a great effect on Debye temperature θ D , isochoric specific heat capacity C V , relaxations time τ , mean free path l , and thermal conductivity κ of monolayer MoS 2 . With the increasing temperature, θ D and C V increase rapidly and then reach saturation, whereas τ and l decrease sharply and then become moderate. The saturation value of θ D and C V of monolayer MoS 2 is 603 K and 17.6 cal/cell K, respectively. The κ of monolayer MoS 2 illustrates the expected T −1 dependence in the range from 47 to 603 K, and it is dominated by longitudinal acoustic (LA) mode which has the maximum value of τ and l . At room temperature, the calculated κ of monolayer MoS 2 of 29.2 W m −1 K −1 is higher than 1.35 W m −1 K −1 that was obtained by Molecular dynamics, but it is in agreement with the experimental value of 34.5 ± 4 W m −1 K −1 . [ABSTRACT FROM AUTHOR]

The structural, elastic, and mechanical properties of the available experimental and theoretical phases of germanium dioxide (GeO 2 ) are investigated. Germanium dioxide (GeO 2 ) is an important material in science and technology due to its wide-ranging applications, and many researches have been proposed to investigate its crystalline polymorphs. Although many phases have been reported, the systematic analysis and comparison of various phases are still lacking. In our paper, the energy, structural, elastic, mechanical properties and mechanical stability of the available experimental and theoretical phases of GeO 2 are investigated from first-principles within the density-functional theory (DFT) plus the local density approximation. The order of increasing ground-state energy is as follows: P 4 2 / mnm , Pnnm , P 2 1 / c , Pbcn , Pnma , P 3 2 21 ( P 3 1 21), P 4 1 2 1 2, C 2/ c , P 6 3 / mmc , P a 3 ¯ , P 4/ mcc , P 6 2 22, C 222 1 , P n 3 ¯ m and P 6 ¯ 2 m , indicating that tetragonal P 4 2 / mnm phase and hexagonal Fe 2 P-type P 6 ¯ 2 m phase have minimum and maximal ground-state energy, respectively. The structural parameters, elastic constants, bulk modulus, shear modulus, Young׳s modulus, Poisson׳s ratio, Lamé׳s constants as well as mechanical stability have been obtained and discussed, indicating that P 6 2 22 and P 6 ¯ 2 m phases are unstable under zero pressure. These results may help to understand GeO 2 for future applications. [ABSTRACT FROM AUTHOR]

Using the first-principles density functional theory, we have studied the structural, elastic, mechanical, electronic and optical properties of the layered ternary nitrides SrZrN 2 and SrHfN 2 . The calculated ground state properties of SrZrN 2 and SrHfN 2 are in agreement with the available experimental data. The independent elastic constants and mechanical properties have been calculated. Results show that SrZrN 2 and SrHfN 2 are all mechanically stable and brittle. SrZrN 2 is a semiconductor with an indirect gap of 0.993 eV and that for SrHfN 2 is 1.139 eV. Moreover, the complex dielectric function, refractive index, extinction coefficient, reflectivity, absorption coefficient, loss function and optical conductivity of two compounds have been calculated. [ABSTRACT FROM AUTHOR]

Abstract: Geometrical, electronic, energetic and thermodynamic properties of the Cu-, Al- and O-terminated CuAlO2(0001) surfaces have been studied by first-principles density functional theory (DFT) calculations. The atomic displacements and surface relaxations of four different terminations were taken into account. According to the results of the surface electronic properties, the Cu-terminated and Al-terminated CuAlO2(0001) surfaces are metallic, and the OI and OII surfaces present the p-type semiconductor surfaces. The surface energies and thermodynamic stability of CuAlO2(0001) surfaces have been analyzed, indicating that the OI surface is the thermodynamically most stable termination. [Copyright &y& Elsevier]

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: Electronic structure and elastic properties of MgCu2, Mg2Ca and MgZn2 phases were investigated by means of first-principles calculations from CASTEP program based on density functional theory (DFT). The calculated lattice parameters were in good agreement with the experimental and literature values. The calculated heats of formation and cohesive energies shown that MgCu2 has the strongest alloying ability and structural stability. The elastic constants of MgCu2, Mg2Ca and MgZn2 phases were calculated, the bulk moduli, shear moduli, Young's moduli and Poisson's ratio were derived. The calculated results shown that MgCu2, Mg2Ca and MgZn2 are all ductile phases. Among the three phases, MgCu2 has the strongest stiffness and the plasticity of MgZn2 phase is the best. The density of states (DOS), Mulliken electron occupation number and charge density difference of MgCu2, Mg2Ca and MgZn2 phases were discussed to analyze the mechanism of structural stability and mechanical properties. [Copyright &y& Elsevier]

Highlights: [•] Molecular crystalline NH4N3 and N2H5N3 have been studied. [•] NH4N3 and N2H5N3 are energetically stable. [•] Ionic bonds between in NH4N3 have been shown. [•] Ionic bonds between in N2H5N3 have been presented. [Copyright &y& Elsevier]

Abstract: A first-principles study based on the density functional theory has been carried out to investigate the electronic and optical properties of zinc-blende GeC1− x B x with various boron concentrations. The calculated lattice parameters of zinc-blende GeC are in good agreement with the previous computations, and the substitution of C with B in GeC induces an increase in the lattice parameters. The calculated results show that the band gap of GeC transforms from indirect band gap to direct band gap and shrinks after C atom is replaced by B atom. The static dielectric constants of B-doped GeC are found to be remarkably large, so it may act as a new dielectric material. Furthermore, after B doping, a new absorption peak appears in the infrared band (0–2eV) and will intensify with the increase of doping concentration. All the calculated optical properties show a red shift property. [Copyright &y& Elsevier]

Abstract: On the plane-wave ultrasoft pseudopotential technique based on the first-principles density functional theory (DFT), we calculated the structural, elastic, electronic and optical properties of the seven different phases of SrZrO3. The obtained ground-state properties are in good agreement with previous experiments and calculations, which indicate that the most stable phase is orthorhombic Pnma structure. Seven phases of SrZrO3 are mechanically stable with cubic, tetragonal and orthorhombic structures. The mechanical and thermodynamic properties have been obtained by using the Voigt–Reuss–Hill approach and Debye–Grüneisen model. The electronic structures and optical properties are obtained and compared with the available experimental and theoretical data. [Copyright &y& Elsevier]

Abstract: We report a direct computational result of a phase transformation from the 3R phase to the 2H phase in CuAlO2 with the application of tensile stress using the first-principles density functional theory calculations. The calculations of enthalpy variation with tensile stress indicates the 3R-to-2H phase transformation is expected to occur around . As the applied tensile stress increases, the independent elastic constants of 3R– and 2H–CuAlO2 show the presences of mechanical instability at −27.5 and , which are possibly related with the ideal tensile strength. [Copyright &y& Elsevier]

Abstract: Structural parameters, elastic, electronic, bonding and optical properties of rutile GeO2 and α-quartz GeO2 have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density functional theory (DFT). The ground-state properties obtained by minimizing the total energy are in favorable agreement with the previous work. Two phases of GeO2 are found to be elastically stable and we have derived the bulk, shear and Young’s modulus, Poisson coefficient for rutile GeO2 and α-quartz GeO2. We estimated the Debye temperature of rutile GeO2 and α-quartz GeO2 from the acoustic velocity. Electronic and chemical bonding properties have been studied from the calculation of band structure, density of states and charge densities. Furthermore, in order to clarify the mechanism of optical transitions for rutile GeO2 and α-quartz GeO2, the complex dielectric function, refractive index, extinction coefficient, optical reflectivity, absorption coefficient, energy-loss spectrum and the complex conductivity function are calculated, which show the significant optical anisotropy in the components of polarization directions (100) and (001) for rutile GeO2 and α-quartz GeO2. [ABSTRACT FROM AUTHOR]

Abstract: Structural parameters, elastic, electronic, bonding and optical properties of delafossite CuAlO2 have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The ground-state properties obtained by minimizing the total energy are in favorable agreement with the previous work. We have derived the bulk, shear and Young''s modulus, Poisson coefficient for delafossite CuAlO2. We estimated the Debye temperature of CuAlO2 from the acoustic velocity. Electronic and chemical bonding properties have been studied throughout the calculation of band structure, density of states and charge densities. Furthermore, in order to clarify the mechanism of optical transitions for delafossite CuAlO2, the dielectric function is calculated, which shows a significant optical anisotropy in the components of polarization directions (100) and (001). [Copyright &y& Elsevier]

Unlike traditional group‐6 transition metal dichalcogenides (TMDs), group‐10 TMDs such as PtSe2 and PdTe2 possess highly tuneable indirect bandgaps, transitioning from semiconducting in the near‐infrared to semimetal behavior with a number of monolayers (MLs). This opens up the possibility of TMD‐based mid‐infrared and terahertz optoelectronics. Despite this large potential, the optical properties of such materials have shown an extremely large disparity between that predicted and measured. For example, simulations show that a few MLs is required for the semiconductor–semimetal transition, whilst tens of MLs is found experimentally. This is a result of widely used optical extrapolation methods to determine bandgaps, such as the Tauc plot approach, that are not adapted here owing to i) nearby direct transitions, ii) the material dimensionality and iii) large changes in the non‐parabolic bandstructure with MLs. Here, uniquely combining optical ellipsometry to determine the complex permittivity, terahertz time resolved spectroscopy for the complex conductivity and in‐depth density functional theory (DFT) simulations, it is shown that the optical properties and bandstructure can be determined reliably and demonstrate clearly that the semiconductor‐semimetal transition occurs for PtSe2 layers ≈5 MLs. The microscopic origins of the observed transitions and the crucial role of the Coulomb interaction for thin semiconducting layers, and that of interlayer van der Waals forces for multilayer semimetallic samples are also demonstrated. This work of combining complimentary experimental techniques and extensive simulations avoids the application of constrained extrapolation methods to determine the optical properties of group‐10 TMDs, and will be of importance for future mid‐infrared and terahertz applications. [ABSTRACT FROM AUTHOR]