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Many studies nowadays are available to predict the half-metallic behaviour of Heusler's quaternary compounds. Using the first principle study of the quaternary Heusler CoZrFeP, we examined its structural, electronic and magnetic properties with the full-potential linearized augmented plane wave (FP-LAPW) method within the generalized gradient approximation (GGA) and the generalized modified potential plus Becke-Johnson approximation (GGA-mBJ). Our quaternary Heusler CoZrFeP compound has shown a half-metallic ferromagnetism character with a small band gap in the minority spin which makes it an excellent candidate for the development of new devices in spintronic and magnetoelectronic. In order to know whether our Heusler quaternary CoZrFeP compound can be experimentally synthesized, we studied its mechanical stability by calculating its formation energy, cohesion energy and elastic constants. [ABSTRACT FROM AUTHOR]

Our aim in this paper is to study the influence of doping with transition metals (TM) on the physical properties of CdS. Thus, the structure stability, half-metallic ferromagnetic, and electronic properties of Cr-, V-, Mn-, Cu-, and Sc-doped CdS, at x = 0.0625 concentration have been investigated using first principle calculations based on the density functional theory (DFT). The all-electron full-potential linear Muffin-Tin orbital (FP-LMTO) method and the generalized gradient approximation (GGA) have been employed. The electronic properties indicate that the Cd0.9375Cu0.0625S and Cd0.9375Sc0.0625S compounds are magnetic degenerate semiconductors and the Cd0.9375Mn0.0625S compound is p-type magnetic semiconductor, while the Cd0.9375Cr0.0625S and Cd0.9375V0.0625S compounds are half-metallic ferromagnets. We have also found that the TM-3d states are responsible for the spin-polarization and the induction of magnetic moments in these compounds. Additionally, to explain the origin of half-metallic ferromagnetism, we have calculated the exchange splitting energy Δx(pd) and the exchange constants N0α and N0β. The calculated values suggest that the Cd0.9375Cr0.0625S and Cd0.9375VV0.0625S compounds may be useful for the development of spintronic devices. [ABSTRACT FROM AUTHOR]

Ammonia (NH3) electrosynthesis gains significant attention as NH3 is essentially important for fertilizer production and fuel utilization. However, electrochemical nitrogen reduction reaction (NRR) remains a great challenge because of low activity and poor selectivity. Herein, a new class of atomically dispersed Ni site electrocatalyst is reported, which exhibits the optimal NH3 yield of 115 µg cm−2 h−1 at –0.8 V versus reversible hydrogen electrode (RHE) under neutral conditions. High faradic efficiency of 21 ± 1.9% is achieved at ‐0.2 V versus RHE under alkaline conditions, although the ammonia yield is lower. The Ni sites are stabilized with nitrogen, which is verified by advanced X‐ray absorption spectroscopy and electron microscopy. Density functional theory calculations provide insightful understanding on the possible structure of active sites, relevant reaction pathways, and confirm that the Ni‐N3 sites are responsible for the experimentally observed activity and selectivity. Extensive controls strongly suggest that the atomically dispersed NiN3 site‐rich catalyst provides more intrinsically active sites than those in N‐doped carbon, instead of possible environmental contamination. This work further indicates that single‐metal site catalysts with optimal nitrogen coordination is very promising for NRR and indeed improves the scaling relationship of transition metals. [ABSTRACT FROM AUTHOR]

First-principle calculations were performed to study electronic structures and magnetic properties of V-doped LiZnAs, as well as the effect of Li interstitial. The results showed that the magnetism origin of V-doped LiZnAs could be explained by p – d hybridization and the ferromagnetic (FM) state of the system was the ground state. The introduction of Li interstitials increased the distance between V and As atoms, which impaired the hybridization of V- 3 d and As- 4 p. As a result, the magnetic moment of V atom increased but the stability of FM coupling between V impurities was weakened. [ABSTRACT FROM AUTHOR]

The existence of spontaneous magnetization in low dimensional magnetic systems has attracted intensive studies since the early 60s and research remains very active even now. Only recently, magnetic van der Waals (vdW) systems down to a few layers have been broadly discussed for their magnetic order ground states at finite temperature. The naturally inherited layered structure of the vdW magnetic systems possessing onsite magnetic anisotropy from band electrons can suppress the long‐range fluctuations. This provides an excellent vehicle to study the transition of magnetism to 2D limits both theoretically and experimentally. Here the current status of 2D vdW magnetic system and its potential applications are briefly summarized and discussed. [ABSTRACT FROM AUTHOR]

The B 6 Be 2 and B 8 Be 2 clusters, adopting fascinating inverse sandwich-like geometries, were recently predicted with quantum chemical calculations. Both systems exhibit the high stability and double aromaticity with 4σ/6π or 6σ/6π delocalized electrons. The hydrogen storage of two systems is studied in the present paper. Our calculations show that B 6 Be 2 and B 8 Be 2 clusters have the ultra-high capacity hydrogen storage, each Be site can bound up with seven H 2 molecules, corresponding to a gravimetric density of 25.3 wt percentage (wt%) for B 6 Be 2 and 21.1 wt% for B 8 Be 2 , respectively, which far exceeds the target (5.5 wt%) proposed by the US department of energy (DOE) in 2017. The average absorption energies of 0.10–0.45 eV/H 2 for B 6 Be 2 and 0.11–0.50 eV/H 2 for B 8 Be 2 at the w B97XD level suggest that both systems are ideal for reversible hydrogen storage and release. The reversibility of H 2 molecules on B 6 Be 2 and B 8 Be 2 complexes are faithfully demonstrated with the Born-Oppenheimer molecular dynamics (BOMD) simulations. The Be-doped boron nanostructure is a promising candidate for ultra-high hydrogen storage materials. The inverse sandwiches B 6 Be 2 and B 8 Be 2 exhibit ultra-high capacity hydrogen storage. The gravimetric densities reach up to 25.3 wt% for B 6 Be 2 and 21.1 wt% for B 8 Be 2 , which are 4.6 and 3.8 times larger than the target (5.5 wt%) proposed by US department of energy (DOE) in 2017. Image 1 • The B 6 Be 2 and B 8 Be 2 clusters have the high stability and double aromaticity. • The B 6 Be 2 and B 8 Be 2 clusters exhibit the ultra-high capacity hydrogen storage. • The gravimetric density of B 6 Be 2 and B 8 Be 2 reaches up to 25.3 wt% and 21.1 wt%. • The Be-doped boron nanostructure is a promising candidate for hydrogen storage. [ABSTRACT FROM AUTHOR]

The atomic structure, interfacial charge distribution, bonding nature, and interfacial electronic states of a 4H–SiC/TiN interface are systematically investigated to understand the Ohmic contact formation mechanisms of TiN to 4H–SiC. The experiment results clearly demonstrate that the well-arranged TiN (111)-oriented lattice planes are parallel to the (0001) SiC-oriented substrate, which is in line with the XRD results. In addition, the interface is coherent without any secondary phase layers, amorphous layers, or transition regions, which confirms the direct contact of TiN to SiC at the atomic scale, exhibiting a linear current–voltage relationship. Quantitatively, first-principle calculations reveal that the Schottky barrier height (SBH) is as low as 0.03 eV and that the band gap nearly vanishes at the interface, indicating an excellent Ohmic contact of TiN to 4H–SiC. Furthermore, the SBH is significantly reduced through the interfacial charge polarization effect and strong coupling of interfacial electronic states, enhancing the quantum electron transport. The present results provide insight into the complicated electronic effects of the Ohmic contact interface and indicate that TiN is a promising SiC Ohmic contact material for advanced next-generation power device applications. [ABSTRACT FROM AUTHOR]

Molybdenum-doped on Cu(II) adsorption of silica was investigated by using first-principle calculations based on density functional theory. The Monte Carlo simulation showed that Cu(II) adsorbed onto the surface of this nanomaterial and in the interstitial spaces between atoms, during the adsorption process, ΔH < 0 and ΔS < 0. Adding a small amount of molybdenum oxide contribute to Cu(II) adsorption. The molecular simulation agreed well with experimental results. [ABSTRACT FROM AUTHOR]

The effect of Cr content on the microstructure and mechanical properties of Cr x FeNiCu high entropy alloys (HEAs) was firstly studied by first-principles calculations. The calculated results show that the hardness of the alloys increased with the expense of its plasticity decrease, if the content of Cr in the alloy increased. In order to verify the calculated results, Cr x FeNiCu (x = 0.8, 1, 1.5 and 2) high entropy alloys were synthesized by vacuum induction melting in the present study. The results show that as the value of x increased from 0.8 to 2, the crystal structure changed from single phase face centered cubic (FCC) phase to a mixture of FCC and body centered cubic (BCC) phases. For the single phase FCC (x = 0.8) structure, both the tensile strength and hardness values were low, which were 491.6 MPa and 322.2 HV respectively, however, the plasticity was high, reaching 33.2%. With the formation and growth of BCC phase (x = 2) the tensile strength and hardness of the alloy were significantly improved, which were 872.6 MPa and 808 HV, respectively. Image 1 • With the increase of Cr content, the microstructures of Cr x FeNiCu high entropy alloys changed from FCC single phase to BCC + FCC duplex phases. • The strength and hardness of the alloys were enhanced as an increase of Cr content from first-principles calculations and experiments. • Solution strengthening, grain boundary strengthening and structural strengthening were the main strengthening mechanisms. [ABSTRACT FROM AUTHOR]

Materials with superhard and conductive properties are valuable and have great potential applications in multifunctional devices under extreme conditions. Here we propose two carbon polymorphs with superior superhard and conductive properties via first-principle calculations. These two carbon phases, called Orth-C 10 and Orth-C 10 ', contain 10 carbon atoms buckled through sp 2- sp 3 hybridized bonds in an orthorhombic unit cell with Pmmm and Pmm 2 symmetry, which are energetically more stable than fullerene C 60 at 0 GPa, and more favorable than graphite at the pressure above 34.4 and 45.4 GPa, respectively. More importantly, their Vickers hardness are as high as 62.2 and 59.9 GPa, respectively, close to the hardness of cubic boron nitride, the second-hardest material. Specially, Orth-C 10 ' owns ultra-high axial incompressibility even beyond that of diamond at a pressure above 40 GPa. Furthermore, both Orth-C 10 and Orth-C 10 ' are metallic, which is rare in superhard carbon polymorphs. These outstanding natures make Orth-C 10 and Orth-C 10 ' potential materials for electronic devices and mechanical tools. Superhard orthorhombic carbon allotropes with conductivity. Image 1 [ABSTRACT FROM AUTHOR]

Synthesis of the powders is critical for achieving the extensive applications of high‐entropy carbides (HECs). Previously reported studies focus mainly on the high‐temperature (>2000 K) synthesis of HEC micro/submicropowder, while the low‐temperature synthesis of HEC nanopowders is rarely studied. Herein we reported the low‐temperature synthesis of HEC nanopowders, namely (Ta0.25Nb0.25Ti0.25V0.25)C (HEC‐1), via molten salt synthesis for the first time. The synthesis possibility of HEC‐1 nanopowders was first theoretically demonstrated by analyzing lattice size difference and chemical reaction thermodynamics based on the first‐principle calculations, and then the angular HEC‐1 nanopowders were successfully synthesized via molten salt synthesis at 1573 K. The as‐synthesized nanopowders possessed the single‐crystal rock‐salt structure of metal carbides and high compositional uniformity from nanoscale to microscale. In addition, their formation mechanism was well interpreted by a classical molten salt‐assisted growth. [ABSTRACT FROM AUTHOR]

By first-principle study, we propose a possible stable helium-based compound with chemical formula of Na2HeO. It has a structure of space group F m − 3 m. Energy calculation indicates that it has a local minimum with a lattice constant a = 4. 0 7 Å. Electronic band structure suggests that it is a wide gap insulator. Analysis on Hirshfeld charges and charge density distribution shows a chemical bond formed between O and He atoms in this structure. Results from both elastic constants and phonon dispersion indicate that this compound in the proposed structure is both mechanically and dynamically stable. [ABSTRACT FROM AUTHOR]

High energy density, low cost, and environmental friendliness are required for modern energy‐storage technologies. The anchoring performance of newly fabricated porous triphenylene–graphdiyne (TPGDY), boron–graphdiyne (BGDY), and nitrogen–graphdiyne (NDGY–C18N6, NGDY–C24N4, and NGDY–C36N6) monolayers are studied by employing density functional theory (DFT). It is found that the porous graphdiyne‐based materials offer more space to accommodate lithium polysulfides with moderate adsorption energies and the anchoring performance changes with substrate and the size of Li2Sn molecules: BGDY has a strong chemical interaction with lithium polysulfides due to the large charge transfer as compared to others. The chemical interaction dominates in anchoring species Li2Sn with small size (n = 1, 2), whereas vdW interaction dominates for S8 and larger size Li2Sn (n = 6, 8) species. Furthermore, anchoring lithium polysulfides reduces the band gaps of the graphdiyne‐based materials and enhances the electronic conductivity. These intriguing features suggest that graphdiyne‐based porous 2D structures are promising anchoring materials for lithium–sulfur batteries. [ABSTRACT FROM AUTHOR]

van der Waals heterostructures (vdWHs) have attracted significant interest as unique structures for application in nanoelectronic devices. A novel BC 6 N/ZnO vdWH was prepared by superimposing BC 6 N semiconductor wafers onto a hexagonal ZnO monolayer. The electronic structure, optical absorptivity, and power conversion efficiency (PCE) of BC 6 N/ZnO vdWH under tensile strain were studied using first-principles calculations. The band structure of the BC 6 N/ZnO vdWH exhibited a type-I band alignment with a direct bandgap of 1.92 eV. The type-I direct bandgap transformed into a type-II indirect bandgap when the uniaxial and biaxial tensile strains were increased to 10 %. Although the bandgap of the BC 6 N/ZnO vdWH increased (from 1.92 to 2.20 eV) monotonically with uniaxial strain (0–10 %), it was nearly independent of biaxial strain. The BC 6 N/ZnO vdWH exhibited a wide range and strong optical absorption in the ultraviolet (UV)–visible range; the absorptivity curve was red-shifted, and the optical absorptivity significantly increased in the UV region with increasing tensile strain. The PCE of BC 6 N/ZnO vdWH reached 22.5 % and 15.3 % under 10 % biaxial and uniaxial strains, respectively. The tunable electronic structure, excellent optical absorptivity, and ultrahigh PCE of BC 6 N/ZnO vdWH can be used in designing two-dimensional high-efficiency photovoltaic devices. [Display omitted] • A novel type-I BC 6 N/ZnO van der Waals heterostructure with a direct bandgap of 1.92 eV was investigated. • The BC 6 N/ZnO heterostructure exhibits type-II indirect bandgap under 10 % tensile strain. • The BC 6 N/ZnO shows improved optical absorptivity and a red-shifted absorption curve under tensile strain. • BC 6 N/ZnO exhibits an ultrahigh PCE (22.5 % and 15.3 %) under 10 % tensile (biaxial and uniaxial) strain. • The electronic and optical properties of BC 6 N/ZnO can be modulated by tensile strain. [ABSTRACT FROM AUTHOR]

The interstitial defects play a crucial role in controlling the irradiation performance of high-entropy alloys (HEAs) particularly of CrMnFeCoNi. However, the site-to-site chemical and magnetic disorder of HEAs prohibits understanding the behavior of interstitials in HEAs. Herein we demonstrate that the chemical bonding dominates the formation of dumbbells at the weak magnetic effect, whereas the strong magnetic effect can perform over the chemical bonding in determining the formation of dumbbells. Accordingly, Ni-containing dumbbells are particularly unstable due to its weak chemical bonding and magnetic effect, while the spin-down Cr and the magnetic adaptive Mn are essential for stabilizing CrMnFeCoNi. Note that the chemical bonding and magnetic effects can be quantitatively characterized by the cohesive and band-filling descriptors. Our study elucidates a physical understanding of the dumbbell interstitials of HEAs and provides a rational guidance for designing advanced structural alloys with optimal irradiation resistance. [Display omitted] [ABSTRACT FROM AUTHOR]

Traditional HfC- and ZrC-based coatings for C/C composites had loose oxide films after long-term ablation, limiting their application above 2000 ℃. In this work, through adjusting the TaC content, the formation of stable and dense Hf-Zr-Ta-O compound films composed of Ta-doped (Hf, Zr)O 2 and (Hf, Zr) 6 Ta 2 O 17 prolonged the service life of HfC-ZrC coating. Additionally, the first-principle calculation based on the VASP software helped to understand the solid solution process among multi-component oxides (HfO 2 , ZrO 2 and Ta 2 O 5) of TaC-modified HfC-ZrC coatings during ablation. As for HfC-ZrC coating, the formed (Hf, Zr)O 2 skeleton was loose and hard to resist long-term ablation (less than 180 s). A small amount of Ta 2 O 5 diffused to (Hf, Zr)O 2 and produced the stable and dense Ta-doped (Hf, Zr)O 2 and (Hf, Zr) 6 Ta 2 O 17 oxide films, increasing the ablation resistance of the HfC-ZrC-TaC coating (5:5:1, more than 180 s). Excessive Ta 2 O 5 was damaged by mechanical denudation during ablation, failing HfC-ZrC-TaC coatings (3:3:1 less than 180 s and 1:1:1 less than 120 s). • The oxidation of TaC lagged behind HfC/ZrC and the oxidation sequence of these elements was Hf ≥ Zr ＞ Ta. • Through first-principle calculations, VASP was used to study the solid solution process among multi-oxides during ablation. • The formation of the stable Hf-Zr-Ta-O compound film increased the ablation resistance of HfC-ZrC-TaC-related coatings. [ABSTRACT FROM AUTHOR]

Designing new anode materials with high performance is vital for the development of full-cell potassium-ion batteries (KIBs). Although boron-doped graphene (BDG) anodes have been widely studied for lithium- and sodium-ion batteries, there are few works considering BDG anodes with controllable doping concentration applied for KIBS. Herein, by first-principle calculations, we propose a novel BDG with controllable doping concentration as a promising anode material for KIBs. As a result, the chemisorption ability of the proposed BDG (BC _20 ) for K is greatly enhanced in comparison with the pristine graphene, since the B dopants introduce electron-deficiency. Besides, the diffusion energy barrier of K on the surface of BC _20 is as low as 0.19 eV, indicating high-rate performance. Noticeably, the maximum K storage capacity is 854 mAh g ^−1 with a low open circuit voltage (OCV) of 0.29 V. Moreover, the chemical window of OCV is in a low range without large variation, which is favorable for providing a large operating voltage. The results suggest that the presented BC _20 is not only a promising anode candidate for KIBs; but also opens an avenue for designing novel BDG structures with controllable doping concentration applied to energy storage.

An air pollution detector is proposed based on a tube-shaped single-electron transistor (SET) sensor. By monitoring the flow control component of the detector, each air pollutant molecule can be placed at the center of a SET nanopore and is treated as an island of the SET device in the same framework. Electron transport in the SET was incoherent, and the performances of the SET were sensitive at the single molecule level. Employing first-principles calculations, electronic features of an air pollutant molecule within a tube-shaped SET environment were found to be independent of the molecule rotational orientations with respect to axis of symmetry, unlike the electronic features in a conventional SET environment. Charge stability diagrams of the island molecules were demonstrated to be distinct for each molecule, and thus they can serve as electronic fingerprints for detection. Using the same setup, quantification of the air pollutant can be realized at room temperature as well. The results presented herein may help provide guidance for the identification and quantification of various types of air pollutants at the molecular level by treating the molecule as the island of the SET component in the proposed detector.

In this paper, we use the first-principles calculations based on the density functional theory to investigate structural, electronic and magnetic properties of Fe_2YSn with (Y = Mn, Ti and V). The generalized gradient approximation (GGA) method is used for calculations. The Cu2MnAl type structure is energetically more stable than the Hg_2CuTi type structure. The negative formation energy is shown as the evidence of thermodynamic stability of the alloy. The calculated total spin moment is found as 3μ_B and 0μ_B at the equilibrium lattice constant for Fe_2MnSn and Fe_2TiSn respectively, which agrees with the Slater-Pauling rule of M_t= Z_t-24. The study of electronic and magnetic properties proves that Fe_2MnSn and Fe_2TiSn full-Heusler alloys are complete half-metallic ferromagnetic materials.

Although Mo5SiB2 is a promising high-temperature material, the role of point defects on the structural stability, mechanical and thermodynamic properties of Mo5SiB2 is unclear. In this study, the first-principles calculations to study the influence of vacancies on the mechanical, electronic and thermodynamic properties of Mo5SiB2 were applied. Three vacancies: B-va, Si-va and Mo-va are considered. The results show that those vacancies are thermodynamically stable in Mo5SiB2. In particular, Mo-va is more thermodynamically stable than that of the B-va and Si-va. The calculated bulk modulus, shear modulus and Young's modulus of the Mo5SiB2 are 271 GPa, 152 GPa and 384 GPa, respectively. Although those vacancies weaken the elastic deformation resistance of Mo5SiB2, they improve its deformation resistance along the c-axis. Importantly, the Mo-va1 improves the thermodynamic properties of Mo5SiB2 in comparison to the other vacancies. Finally, those vacancies result in a band shift from the conduction band to the valence band. [ABSTRACT FROM AUTHOR]

Equilibrium Ti isotope fractionation factors among major Ti-bearing minerals are critical for understanding Ti isotope fractionation during magmatic processes. We use the first-principles calculations based on the density functional theory (DFT) to obtain Ti isotope reduced partition function ratios (103lnβ of 49Ti/47Ti) in a series of important Ti-bearing minerals, including Ti-doped clinopyroxene, orthopyroxene, olivine, and pyrope, geikielite-ilmenite solid solutions, and rutile. There is a large variation in our calculated 103lnβ, which are linearly correlated to their Ti force constants, a parameter related to the average Ti O bond length and the Ti valence state. Among all studied minerals, silicates with Ti4+ occupying the tetrahedral Si site have the highest 103lnβ, and rutile has the lowest 103lnβ. The valence state also significantly controls the 103lnβ. Typically, Ti3+-doped silicates have lower 103lnβ than those of Ti4+-doped silicates. At the natural abundance levels, the 103lnβ of Ti4+ Si -doped and Ti3+ Mg -doped (Ti3+ occupying the Mg site) silicate minerals show no concentration effect. That is, their 103lnβ do not vary with their Ti4+ and Ti3+ contents, respectively. In contrast, the 103lnβ of geikielite-ilmenite solutions significantly decrease with increasing Fe/(Fe + Mg) ratio. Our calculations predict no significant Ti isotope fractionation among Ti4+ Si -doped clinopyroxene, orthopyroxene, olivine, and pyrope (<0.08 % at 1200 K), whereas the 103lnα between geikielite-ilmenite solutions and Ti4+ Si -doped clinopyroxene ranges from ∼−0.67‰ to −0.49‰ at 1200 K, supporting the hypothesis that Fe Ti oxides are important fractionating Ti isotopes during magma differentiation. Finally, the large equilibrium Ti isotope fractionation between geikielite-ilmenite solutions and clinopyroxene suggests that Ti isotopes can be used as a thermometer with precision comparable to that of elemental geothermometer. [ABSTRACT FROM AUTHOR]

Owing to the unique merits benefited from the two‐dimensional (2D) geometry, graphene has been often chosen as an attractive strength enhancer during the design of metal‐graphene structural composites. In spite of the improved mechanical properties with the assistance of graphene, it is still challenging to fit the strength requirements for these metal‐graphene composites in the practical applications. To address this issue, metal‐doping and carbon‐vacancy engineering, in this work, are first proposed to manipulate the dual‐phase interfaces between metal and graphene in order to further strengthen the mechanical properties in metal‐graphene composites based on the first‐principle calculation. It can be concluded that a single‐carbon‐vacancy graphene or a Ti, Mn‐doped metal matrix in metal‐graphene composites delivers the best interfacial binding capability, resulting in an obvious strength increase of over 110% for Cu‐graphene composites. Finally, the deformation mechanisms of metal‐graphene composites are discussed via the evaluation on tensile deformation processes, electron densities, and stacking fault energies. This work offers us an alternative solution for the effective reinforcement on mechanical properties of metal‐graphene composites by manipulating the dual‐phase interfaces using doping or vacancy engineering. [ABSTRACT FROM AUTHOR]

In this work, the phase transitions, the elastic properties, and the electronic properties of Sr8Al16Sn30 under different pressures are investigated by first-principle calculations based on density functional theory. The E–V curves show that the type-VIII is the stable ground state phase, while the type-I is considered to be metastable at the lowest energy. Ignoring the temperature effect, type-VIII clathrate is always more stable than type-I, and the indication of phase transitions from type-I to type-VIII structure is not observed under increasing hydrostatic pressure. The obtained elastic constant values indicating that two structures under 0 and 3 GPa are stable, and not stable under 7 GPa. The dependences of the elastic constants cij, the elastic modulus, the Poisson ratio, the brittle and ductile behavior, and the elastic anisotropy on pressure in two structures are further analyzed. The electronic structures of type-I and type-VIII clathrates significantly change under increased pressure. The type-I clathrate with a narrow gap turns into the metal, and for type-VIII the band gap decreases in 3 GPa and the band gap increases in 7 GPa. This show that pressure tuning plays an important role in improving material properties. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

First-principles calculations were performed to investigate the catalytic activity of Li O 2 batteries based on TiC and X-doped TiC (X = B, N, Al, Si, and P) materials as potential cathode catalysts. Interfacial models of Li x O 2 (x = 4, 2, and 1) intermediates adsorbed on doped TiC surface were used to simulate the structural evolution during discharging/charging process. The catalytic activity was quantitatively assessed by specific ORR/OER overpotential, and some intrinsic factors affecting the catalytic activity of doped TiC were determined based on the structure-activity relationships established. The catalytic activity of doped TiC can be divided into two groups, wherein B-, N-, and P-doped TiC have better catalysis than Al- and Si-doped TiC. Among them, B-doped TiC displays the lowest ORR overpotential, suggesting that B-doped TiC has the best catalytic activity of ORR. The stronger (Li 2 O) 2 /Li 2 O 2 /LiO 2 adsorption energy induces lower ORR and OER overpotentials. The stronger Li+ desorption energy attracts lower ORR overpotential, while the weaker O 2 desorption energy induces lower OER overpotential. Consequently, adsorption energy of (Li 2 O) 2 /Li 2 O 2 /LiO 2 and desorption energy of Li+/O 2 are useful factors for characterizing the catalytic activity. These findings contribute to understand the doping effect on catalysis and provide insights into the screening and design of novel catalyst in Li O 2 batteries. • The calculated catalytic activities of doped TiC materials in Li O 2 batteries have been provided. • Intrinsic factors relative to adsorption/desorption behavior of active molecules are determined. • Strategies of cation doping or co-doping are suggested to improve the catalytic activity of TiC materials. [ABSTRACT FROM AUTHOR]

The electronic and elastic properties of A II B 2 III C 4 VI defect-chalcopyrite semiconductors have been studied using first-principle density functional theory (DFT) calculations. The lattice constants, energy band gap, elastic stiffness constants, bulk modulus, shear modulus, shear anisotropy factor, Young's modulus, Debye temperature, Poisson's ratio and B/G ratio have been computed. The values of elastic constants of 14 defect-chalcopyrites and Debye temperature for 18 compounds have been reported for the first time. The obtained results are in reasonable agreement with the experimental values in few cases where experiments are performed and reported values. [ABSTRACT FROM AUTHOR]

• Graded materials additive manufacturing is beneficial to fabricate TiB 2 /Ti6Al4V multi-materials successfully. • The variations of chemical composition and nanohardness were gradual along the interface. • First-principles calculations demonstrated the axis growth of TiB crystals as well as the different hardness of this system. Selective laser melting (SLM), as a rapidly developed layer-by-layer 3D printing technology, has been demonstrated that it can be used for additive manufacturing of multi-materials. In this work, TiB 2 /Ti6Al4V multi-materials were manufactured by SLM. The results showed that interfacial microstructures consisting of un-melted TiB 2 powders, columnar TiB crystals, and acicular TiB crystals were formed in the molten pool. Meanwhile, a variation nanohardness was developed with chemical compositions at the interfacial regions, owing to an in-situ reaction of Ti and TiB 2. The first-principle calculations were used to reveal the axial growth of TiB crystals as well as the different hardness of this system. [ABSTRACT FROM AUTHOR]

In this paper, the interactions between a H 2 O 2 molecule and anatase TiO 2 (101) (A-TiO 2) surface are studied by first-principle calculations. It is found that a H 2 O 2 molecular can adsorb or dissociate on A-TiO 2 (101) surface, in agreement with previous results. When a H 2 O 2 molecule dissociates, Ti-μ-peroxide configurations may form. It should be noticed that a more stable Ti-μ-peroxide configuration is found in this paper. More interestingly, an oxygen atom of this dissociated H 2 O 2 can enter into A-TiO 2 (101) lattice, i.e. , forming surface (O 2)o. The energy barriers for formations of new Ti-μ-peroxide and surface (O 2)o species are 0.30 and 1.28 eV, respectively, which explain previous experimental results that the formations of Ti-μ-peroxide and (O 2)o species are under lower and higher temperatures, respectively. The localized gap state of Ti-μ-peroxide disappears after the formation of surface (O 2)o, and thus the recombination probability of electron-hole pairs should be reduced for the O-rich A-TiO 2. These results can rationalize experimental results that the photocatalytic activity of A-TiO 2 sample can be changed by H 2 O 2 treating under different temperature. • A deep localized state appears for the OOH/H③ configuration, which is detrimental for the photocatalytic activity. [ABSTRACT FROM AUTHOR]

The structural, electronic and elastic properties of orthorhombic ZnGeN2 and wurtzite (WZ)-GaN semiconductors have been studied under different pressures using first-principle density functional theory (DFT) calculations. The lattice constants (a, b and c) and energy bandgaps ( E g ) have been calculated under ambient condition. The elastic properties such as elastic stiffness constants ( C i j ), shear modulus (G), bulk modulus (B), Young modulus (γ), B/G ratio and Poisson ratio (υ) have been studied at 50, 100, 110, 120, 150, 160, 180 and 190 GPa pressures for the first time as well as at 0 GPa. The calculated values of C i j show that the ZnGeN2 and GaN are stable up to 180 and 150 GPa, respectively, and afterwards phase changes and become unstable. The band structure of ZnGeN2 reveals direct band gap behavior up to 100 GPa and becomes indirect band gap at 110 GPa. However, GaN is direct band gap up to 150 GPa and becomes indirect at 160 GPa. Comparing the results of both semiconductors, it is observed that ZnGeN2 is similar to WZ-GaN up to 100 GPa in all respect and can be used in many applications in place of WZ-GaN. The calculated values of all parameters are in reasonable agreement with the known values. [ABSTRACT FROM AUTHOR]

The synthesis of high‐entropy metal carbide powders is critical for implementing their extensive applications. However, the one‐step synthesis of high‐entropy metal carbide powders is rarely studied. Herein, the synthesis possibility of high‐entropy metal carbide powders, namely (Zr0.25Ta0.25Nb0.25Ti0.25)C (ZTNTC), via one‐step carbothermal reduction was first investigated theoretically by analyzing chemical thermodynamics and lattice size difference based on the first‐principle calculations, and then the ZTNTC powders with particle size of 0.5‐2 μm were successfully synthesized experimentally. The as‐synthesized powders not only had a single rock‐salt crystal structure of metal carbides, but also possessed high‐compositional uniformity from nanoscale to microscale. More interestingly, they exhibited the distinguished coral‐like morphology with the hexagonal step surface, whose growth was governed by a classical screw dislocation growth mechanism. [ABSTRACT FROM AUTHOR]

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First-principle calculations are performed to study the structural, electronic, and optical properties of chair-structured hydrogenated graphene (C-graphane) under different hydrostatic pressures. The lattice constants, bond lengths, bond angles, energy band gap, and binding energy are calculated in the pressure range of 0–300 GPa. The results show that C-graphane is stable up to 250 GPa but becomes unstable at 300 GPa, with direct band gap behavior up to 30 GPa but an indirect band gap at 35 GPa. The optical properties such as the static dielectric constant ε(0), refractive index n(0), birefringence ∆n(0), and plasmon energy (ћωp) are studied at different hydrostatic pressures of 0 GPa, 15 GPa, and 30 GPa for the first time. The calculated values of all the parameters are in reasonable agreement with available experimental and reported values. [ABSTRACT FROM AUTHOR]

• V Si - and V Si 2 - defects can induce local magnetic moments, but V Si 0 defects cannot. • Most of the local moments derive from 2 p states of the nearest-neighbor C atoms. • The coupling between the V Si - defects is AFM, while the V Si 2 - defects favor FM. • 6H-SiC with V Si and N C show the same property as one with V Si added electron. We perform first-principle calculations of silicon vacancies induced ferromagnetism in 6H-SiC. Our results showed that except for V Si 0 defects, both V Si - and V Si 2 - defects can induce local magnetic moments, most of which are derived from the C 2p states of the nearest-neighbor atoms of silicon vacancies. Furthermore, We found the coupling between the V Si - defects is antiferromagnetic, while the V Si 2 - defects favor a ferromagnetic coupling. The 6H-SiC systems with V Si and N C (substitution of carbon atom with nitrogen atom) can show the same properties of spin-polarization and magnetic coupling as the systems of V Si with attached extra electrons, as N C introduces carriers and a higher carrier concentration favors a stable ferromagnetic behavior. Therefore, ferromagnetism in 6H-SiC is determined by both the silicon vacancy and the carrier concentration. Our theoretical calculations provide possible guidance for the design of magnetic SiC. [ABSTRACT FROM AUTHOR]

Based on first-principles calculations, together with the Boltzmann transport equation and semiclassical analysis, we carried out a series of studies on the thermoelectric properties of Li 3 P and Li 3 As, such as the thermal conductivity κ which contains lattice thermal conductivity κ L and electronic thermal conductivity κ e , electron structure, Seebeck coefficient S and electrical conductivity σ , and obtained extremely large Seebeck coefficient S and extraordinary low lattice conductivity κ L which are 2.832 W m−1 K−1 and 2.795 W m−1 K−1 at a temperature of 300 K for Li 3 P and Li 3 As, respectively. Benefited from the intrinsic flat band structure near the Fermi level and the drastic anharmonic phonon scattering, we finally acquired ideal figure of merit ZT values, which are 1.17 and 1.13 for p -type doped Li 3 P and Li 3 As, respectively, the above results indicate that Li 3 P and Li 3 As are promising thermoelectric materials if properly used in the future. • Prominent thermoelectric properties is benefit from the intrinsic at band structure near the Fermi level. • This kind of materials has the drastic anharmonic phonon scattering. • The materials have extremely low lattice thermal conductivity. • The acoustic phonon modes and anharmonic interactions contribute most of the lattice thermal conductivity. [ABSTRACT FROM AUTHOR]

First principle calculations have been performed to study the structural, electronic, optical and thermodynamical properties of hydrofluorinated graphene. The band structure and density of states have been discussed. The optical properties have been described in parallel and perpendicular polarizations of electric field in the energy range of 0–25 eV. Thermodynamic properties have been calculated in the temperature range of 5 K–1000 K and compared with the graphene and hydrogenated graphene. The values of 16 parameters have been calculated, out of which 6 parameters such as static dielectric constant ε(0), refractive index n(0), birefringence Δn(0), conductivity threshold σ(ω), plasmon energy (ћω p) and Debye temperature (Θ D) are calculated for the first time. The obtained results shows direct band gap nature of hydrofluorinated graphene till 400 GPa and stable up to 150 GPa external pressure. The calculated values of all parameters agree well with the available data at 0 GPa. Image 1 • The structural and electronic properties are calculated under different pressures for the first time. • The optical parameters such as ε(0), n(0), Δn(0), σ(ω), ћω p have been calculated for the first time. • Thermodynamic properties have been calculated and compared with hydrogenated graphene and graphene. • The nature of band gap and stability of hydrofluorinated graphene have been calculated under different pressures. • The calculated values agrees well with the reported values. [ABSTRACT FROM AUTHOR]

The high electrochemical performance of Li2MnO3‐derived Li‐rich layered oxides suggests that Na2MnO3 might be a promising cathode material for sodium‐ion batteries for its effective anionic oxygen redox. However, experimental and theoretical evidence for anionic redox and enhanced Na+ capacity of Na2MnO3 has not been established. In the present work, the structural and thermal stability, and the anionic oxygen redox mechanism of Na2MnO3 were studied by using first‐principle calculations based on density functional theory. About 1.75 Na+ per formula unit were extracted from Na2‐xMnO3 through partial O2− oxidation while the local structure remained intact, resulting in a large theoretical capacity of 315 mA h g−1. Surface Na+ was extracted before bulk Na+, which might have led to oxygen loss and structural transformation from the surface to the material bulk. Given the importance of high capacity in practical applications, Na2MnO3 and its derived Na‐rich layered oxides might be considered promising cathode materials for sodium ion batteries. [ABSTRACT FROM AUTHOR]

Developing new optoelectronic devices based on two-dimensional materials is an important research topic at present. In these developments, to construct GaAs/Graphene hetero-structure is becoming research hotspot, which can significantly improve the performance of GaAs-based optoelectronic devices. For the application of optoelectronic devices, the interfacial properties and effects are the key factors. However, these issues are not yet fully explored and understood so far, especially the atom diffusion from GaAs substrate to Graphene active layer. In the present work, the electronic structures and atom transportation of GaAs/Graphene hetero-structures were systematically investigated by First-principle calculations. The Ga or As atom, which diffuses from GaAs substrate to Graphene active layer, can open the zero-band-gap of Graphene. Furthermore, Ga atoms adsorbed onto Graphene is the most obvious to realize the purpose of opening the zero-band-gap of Graphene. Moreover, owing to the existence of interfacial built-in electric field, the electrons can efficiently transfer from GaAs substrate to Graphene active layer. This may be the underlying physical mechanism, by which to improve the optoelectronic performance of GaAs-based devices. The findings in this paper can explain the experimental phenomena reported in some literatures, and are helpful for the development of novel GaAs-based optoelectronic devices in the future. Image 1 • Built-in field is favorable for the separation of electron-hole pairs. • Ga/As atom can diffuse from GaAs surface to Graphene. • Diffused Ga/As atom can open the zero-bandgap of Graphene. • Doping effects of Ga are more obvious than those of As for Graphene. [ABSTRACT FROM AUTHOR]

First-principle alloy theory is employed to explore the ordering-induced elastic anomaly in the FeCoNiAl 1− x Ti x (0 ≤ x ≤ 1) high-entropy alloys. The disordered and partially ordered solid solution structures are quantitatively described within unified models. A comparison is made between the elastic parameters of the hypothetical structures, and the presence of L1 2 phase is found to be responsible for the strong stability in shear deformation in the Ti-rich compositions. The results are in line with experimental observation, and suggest that a proper control of the ordering level can be applied for further optimization of the mechanical characteristics in high-entropy alloys. Unlabelled Image [ABSTRACT FROM AUTHOR]

In this study, the growth of 1-dimensional manganese oxide (δ-MnO 2) nanowire on hierarchical ordered mesoporous carbons/graphene composites (C) was synthesized by a relatively low-cost, simple, effective and eco-friendly redox process. It is found in both experimental results and theoretical simulations that the carbon surface, especially the mesoporous channels of ordered mesoporous carbons (amorphous carbons), would be favorable to serve as the nucleated sites for the growth of MnO 2 nanowires. Likewise, the strong adsorptive interactions between MnO 2 and amorphous carbons result in the high deposition efficiency of MnO 2 on C (98%) and the outstanding stability of MnO 2 -decorated hierarchical porous carbon composites (MnO 2 @C) together with the relatively low equivalent series resistance. This electrode material exhibits excellent electrochemical behavior with a specific capacitance high up to 756.2 F g−1 in KOH electrolytes. In addition, an asymmetric supercapacitor (ASCs) assembled by using MnO 2 @C and C as the positive and negative electrodes in 1.0 M Na 2 SO 4 solution achieves a maximum energy density of 34.56 Wh kg−1 at a power density of 450 Wkg-1 and excellent cycling stability. The results demonstrate the MnO 2 -decorated hierarchical porous carbon composites are promising candidates for the future high-performance supercapacitors. Image 1 • D δ-MnO 2 nanowire decorated hierarchical porous carbon composites are fabricated. • MnO 2 deposited on the surface and mesopores of amorphous carbons, not the micropores. • The specific capacitance of MnO 2 @C high up to 756.2 F g−1 in KOH electrolytes. • The ASCs achieve a maximum energy density 34.56 Wh kg−1 at a power density 450 W kg−1. [ABSTRACT FROM AUTHOR]

By using first-principles calculations, we explore the influences of tensile strain on the magnetic properties of a defective arsenene monolayer with mono-vacancy and di-vacancy. Calculation results show that unstrained defective arsenene monolayers both are intrinsically nonmagnetic. However, appropriate tensile strains can induce a ferromagnetic coupling in mono-vacancy- (8%) and di-vacancy-doped systems (7%), respectively. In addition, we also discussed the physical mechanism of strain-induced magnetism emergence and predicted a possibility of magnetism appearance in the experiment. Our study may provide insight for the design of memory-switching spintronic devices with metal-free magnetism by using arsenene. [ABSTRACT FROM AUTHOR]

Band structures of the functionalized Ti 2 C monolayers. First-principle calculations are performed to study the electronic properties and Na-ion storage capabilities of two-dimensional Ti 2 C MXene monolayers. The surface derivatives, namely Ti 2 CC 2 , Ti 2 CO 2 , and Ti 2 CS 2 , are also considered. The results demonstrate that the bare and terminated monolayers are metallic in character with high electrical conductivity. We find that these monolayers are stable, with Ti 2 C and Ti 2 CO 2 offering the most stable configurations overall. We also consider functionalized Ti 2 C MXenes terminated with -C and -O and find that, compared to S-terminated surfaces, these display better activation adsorption. Theoretical results underscore the excellent adsorption properties of Ti 2 CC 2 and Ti 2 CO 2 and reveal that they have lower energy barriers for sodium diffusion than Ti 2 C. In addition, the results showed that sodium ion adsorption on Ti 2 C monolayers achieved a high adsorption energy (−2.5 to −0.4 eV) during sodiation, which could enhance the motion capabilities of bare and oxide systems. The structural transformation behaviors of bare and terminated Ti 2 C monolayers were confirmed during sodiation by ab initio molecular dynamic simulations. In view of its outstanding capacity, electrical conductivity and high Na-ion diffusivity, we conclude that Ti 2 C and its surface termination group-based monolayers have excellent potential for use as anodes in Na-ion batteries. [ABSTRACT FROM AUTHOR]

The structural and electronic properties of vacancy-doped 1H and 1T′ MoTe 2 monolayers are systematically investigated based on first-principles calculations. Te vacancy is found energetically favored over Mo vacancy for both phases, and Te double vacancy is more favored as it is formed by missing two Te atoms from opposite sides. Vacancy induced defect states are strongly spatially localized on the atoms within two or three shell surrounding the point defect. This strongly localized nature leads to weak dependence of the defect formation energy on defect concentrations, sharply peaked density of states, and flat bands. Moreover, the calculation suggests that Te vacancy opens a band gap in the 1T′ MoTe 2 monolayer, which can be tuned by lattice strain or external force. These results might give a guidance for the research on the application of MoTe 2 in electronics and optoelectronics. • The structure of energetically most favorable monovacancies and double vacancies are theoretically determined in MoTe 2 monolayer for both 1H phase and 1T′ phase. •The localization of defect states as well as their energies are presented. •Vacancy effects on the electronic structure of MoTe 2 monolayer and their dependence on concentration are discussed. [ABSTRACT FROM AUTHOR]

Abstract The electronic structure of lead-free piezoelectric ceramics (K 0 · 5 Na 0.5)NbO 3 and CaZrO 3 -modified (K 0 · 5 Na 0.5)NbO 3 were investigated by using first-principle calculations based on density functional theory. The calculated results show that the doping of Ca reduces the band gap and causes the Fermi surface to move toward the high-energy conduction band, and Ca more easily replaces Na than K. The doping of Zr broadens the band gap, and the Fermi surface moves toward the valence band. The doping of CaZrO 3 makes it easier for KNN to be stretched from the O-phase to the T-phase, which improves the performance of KNN. [ABSTRACT FROM AUTHOR]

Graphical abstract The optimized cubic crystal structure using Xcrysden Software. Highlights • The opto-electronic and thermoelectric behavior of the XIn 2 S 4 (X = Zn, Cd) thiospinels are studied by employing DFT. • Direct and indirect bandgap for ZnIn 2 S 4 and CdIn 2 S 4 respectively are observed. • The optical properties are determined in terms of dielectric constants and refraction. • The ZT values equivalent to unity can be achieved for both thiospinels. Abstract The opto-electronic and thermoelectric properties of the XIn 2 S 4 (X = Zn, Cd) thiospinels are studied by employing the density functional theory (DFT) based methods. The stability of thiospinels has been confirmed by formation energy. Direct and indirect bandgap for ZnIn 2 S 4 and CdIn 2 S 4 respectively are observed. The values of band gaps that are determined with modified Becke and Johnson (mBJ) potential are good agreement with experimental values. The optical and thermoelectric properties are discussed in details. Our calculated values thermoelectric parameters such as ZT values equivalent to unity can be achieved for both thiospinel and make them promising candidate in energy harvesting devices. [ABSTRACT FROM AUTHOR]