First-principles Study Research Articles

Properties of Ti2CO2 and Ti2CO2/G heterostructures as anodes of sodium-ion batteries by first-principles study

Properties of Ti2CO2 and Ti2CO2/G heterostructures as anodes of sodium-ion batteries by first-principles study

Effects of mechanical stress, chemical potential, and coverage on hydrogen solubility during hydrogen-enhanced decohesion of ferritic steel grain boundaries: A first-principles study

Hydrogen-enhanced decohesion (HEDE) is one of the many mechanisms of hydrogen embrittlement, a phenomenon that severely impacts structural materials such as iron and iron alloys. Grain boundaries (GBs) play a critical role in this mechanism, where they can provide trapping sites or act as hydrogen diffusion pathways. The interaction of H with GBs and other crystallographic defects, and thus the solubility and distribution of H in the microstructure, depends on the concentration, chemical potential, and local stress. Therefore, for a quantitative assessment of HEDE, a generalized solution energy in conjunction with the cohesive strength as a function of hydrogen coverage is needed. In this paper, we carry out density functional theory calculations to investigate the influence of H on the decohesion of the Σ5(310)[001] and Σ3(112)[11¯0] symmetrical tilt GBs in bcc Fe, as examples for open and close-packed GB structures. A method to identify the segregation sites at the GB plane is proposed. The results indicate that at higher local concentrations, H leads to a significant reduction of the cohesive strength of the GB planes, significantly more pronounced at the Σ5 than at the Σ3 GB. Interestingly, at finite stress, the Σ3 GB becomes more favorable for H solution, as opposed to the case of zero stress, where the Σ5 GB is more attractive. This suggests that, under certain conditions, stresses in the microstructure can lead to a redistribution of H to the stronger grain boundary, which opens a path to designing H-resistant microstructures. To round up our study, we investigate the effects of typical alloying elements in ferritic steel, C, V, Cr, and Mn, on the solubility of H and the strength of the GBs. Published by the American Physical Society 2024

Insight into graphene/boron arsenide heterostructure used for high-performance lithium-ion battery anode materials: The first principles study

Two-dimensional (2D) van der Waals (vdW) heterostructures demonstrate potential applications in Lithium-ion batteries (LIBs) characterized by their elevated energy storage capacity and extended operational longevity as anode materials. The structures and electronic properties of graphene/boron arsenide (Gr/BAs) heterostructures, along with the adsorption and migration of lithium (Li) atoms within the structures, are methodically analyzed through first-principles studies underpinned by density functional theory. Our calculations indicate the metallic Gr/BAs heterostructures have the structural stability, where their mechanical strength is confirmed from the elastic constant. Its diffusion barrier of Li atoms (0.25 eV) is superior among similar anode materials. The Li atoms' diffusion coefficient within the Gr/BAs heterostructure at 300 K (1.27 × 10−10 m2/s) exceeds that observed in Gr (2.0×10−11 m2/s). Besides, the presence of Gr assists in maintaining the open-circuit voltage (OCV) of Gr/BAs heterostructures in the range of 0-1 V. The theoretical specific capacity of proposed heterostructure reaches 920 mAh/g. The present calculations suggest that the Gr/BAs heterostructure could serve effectively as an anode in LIBs due to its excellent electrical conductivity, small diffusion barriers and appropriate open-circuit voltage.

A First-Principles Study on the Anchoring Properties of Defective Single-Walled Carbon Nanotubes for Lithium-Sulfur Batteries

The application of lithium-sulfur (Li–S) batteries is impeded by the significant polysulfide shuttling phenomenon. Developing suitable anchoring material is an effective way to restrain this behavior. In this work, the anchoring performance of lithium polysulfide (LiPSs) on defective single-wall carbon nanotubes (DSWNT) is investigated by density functional theory. The results demonstrate that the DSWNT with three carbon vacancies (DSWNT-3) has the highest forming capacity and the strongest adsorption capacity, indicating it has the best anchoring effect of LiPSs. As the anchoring material of the cathode, DSWNT-3 has greater energy than solvent molecules to inhibit the dissolution of long-chain polysulfides. In general, DSWNT-3 demonstrates notable efficacy as an anchoring material for Li–S batteries, which establishes a theoretical foundation for exploring the anchoring characteristics of defects and their application in the cathode of Li–S batteries.

Theoretical Study of Dissolved Gas Molecules in Transformer Oil Adsorbed on Intrinsic and TM (Ta, V)-Doped MoTe2 Monolayer.

In this paper, CH4, C2H2, H2, and CO adsorbed on intrinsic MoTe2 monolayer and transition metal atom (Ta, V)-doped MoTe2 monolayer have been investigated with density functional theory based on first-principles study. The adsorption energy, geometries, band structures, and density of states of four gases (CH4, C2H2, H2, and CO) adsorbed on the MoTe2 and doped MoTe2 surfaces were analyzed. The results shown that the gas adsorption performance of transition metal atom (Ta, V)-doped MoTe2 monolayers is more superior than that of intrinsic MoTe2, and the adsorption energy and charge transfer of the adsorbed gases on the TM-MoTe2 monolayer are significantly increased in comparison with both sides. Among them, Ta-MoTe2 has the largest Eads value in the adsorbed CO system with a very small adsorption distance, as well as a more suitable recovery time of CO at room temperature, so Ta-MoTe2 can be a candidate material for CO detection. New atoms were introduced during the doping process, which increased the carrier density and carrier mobility of the material, thus improving the charge transfer at the surface of the material. which provides a direction for the gas-sensitive properties of metal Ta-modified MoTe2 materials.

Higher-order topological Dirac phase in Y3InC: a first-principles study

Higher-order topological insulators hosting intriguing topologically protected hinge or corner states are of significant research interest. However, materials that possess higher-order topological hinge states associated with gapless bulk Dirac phases still need to be explored. Using first-principles calculations with hybrid exchange functional, we explore the electronic structure and topological properties of Y3InC and a few of its sister compounds, totaling 16 bulk materials. A symmetry-protected triple point phase, with dominated d-t 2g character, is observed in Y3InC without spin–orbit coupling (SOC). Interestingly, the SOC induces a twin Dirac node phase in the bulk Y3InC. Furthermore, the computed Z 4 topological invariant reveals the higher-order topological nature of investigated materials. To demonstrate the gapless hinge states, we conduct edge state calculations using a rod-shaped geometry of Y3InC. Remarkably, Y3InC is identified to host multi-Dirac nodes in the bulk and surface phases together with the higher-order hinge states. These results lay the groundwork for further experimental and theoretical investigations into cubic antiperovskite materials for higher-order topological phases.

First-principles studies of the stability, structural, electronic, magnetic and optical properties of halogen atom doped marcasite FeS2

The effects of halogen atom (F, Cl, Br or I) doping on the stability, structural, electronic, magnetic and optical properties of marcasite FeS2 (m-FeS2) are investigated through the first-principles calculations. The formation energies are relatively small under Fe-rich condition, indicating that it is feasible to implant halogen atom into m-FeS2. The ground state of halogen atom doped m-FeS2 systems is magnetic due to the positive energy differences between non-spin-polarized and spin-polarized states. Phonon dispersion curves show that all doping systems are dynamically stable. The total magnetic moment of all doping systems is nearly 1μB, since replacing the S atom with a halogen atom introduces a non-bonding electron. Most of them come from Fe and S atoms, and only a small fraction come from the dopant. The simulation results show that F- and Br-doped m-FeS2 systems are still semiconductors although the band gaps are reduced considerably, Cl-doped m-FeS2 changes to a half-metal with half metallic band gap of 0.25 eV, while I-doped m-FeS2 becomes a metal, making them potentially useful in spintronics. In addition, the halogen atom doped m-FeS2 systems possess enhanced absorption coefficient and red-shifted absorption edge. So they are promising in optoelectronic device and solar energy harvesting.

The First-Principles investigation of sensing and removal applications of nitrobenzene using pristine and Sc decorated B9N9 nanoring

Nitrobenzene (NB), an aromatic organic compound widely used in various industries, has several environmental risks. Due to its risks, reliable sensing mechanisms are crucial. In the present work, we investigated the potential of the pristine and Sc decorated B9N9 nanoring as a sensor for detection of the toxic NB molecule using density functional theory (DFT). We have analyzed the structural parameters, adsorption energy (Ead), highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), HOMO-LUMO gap, density of states (DOS) spectra, Mulliken charge transfer, dipole moment, IR spectra, non-covalent interactions (NCI) iso-surfaces, recovery time (τ) and work function (φ) before and after the adsorption of NB onto pristine and Sc decorated B9N9 nanorings. Our analysis revealed that the NB interacted optimally with the pristine B9N9 nanoring, as evidenced by changes in electronic properties and Ead value of −0.58 eV. However, the Sc decorated B9N9 nanoring indicated a strong interaction with NB with Ead of −4.09 eV at a proximal distance of 2.12 Å. Furthermore, our study demonstrated that the pristine B9N9 nanoring could be used as both an “electronic sensor” and “φ-type sensor”. Additionally, to esteem rapid recovery for practical feasibility, we calculated τ for both the pristine and Sc decorated B9N9 nanoring. The short τ of the pristine nanoring indicates its suitability as NB sensor. In contrast, the longer τ of the Sc decorated nanoring suggests its applicability for NB storage or its removal from the surroundings. Overall, our findings underscore the potential of pristine B9N9 nanoring as effective NB sensor and removal. We hope that our study will assist experimentalists to develope a reliable B9N9 nanoring based sensor for the detection of NB molecules.

A first-principles study of the phase transitions in ultrahigh temperature shape memory alloy RuNb

Ultrahigh temperature shape memory alloys (UHT-SMAs) have transition temperatures above 600 °C. They are needed for sensing and actuating devices in aerospace applications. However, very few such UHT-SMAs have been found. Among them are Ru-based alloys such as RuNb and RuTa, whose martensite structures and phase transitions are totally different from those of NiTi-based SMAs and were poorly understood. In this work, we carried out a systematical study of RuNb using first-principles total energy calculations and molecular dynamics (MD) simulations. We revealed the transition paths and mechanisms in cubic → tetragonal → monoclinic transitions. We determined the transition sequence and martensitic transition temperatures (MTTs) by evaluating the Gibbs free energies using thermodynamic integration. The calculated MTTs are in very good agreement with the experimental data. We also found that the monoclinic phase at the second transition has the P21/m symmetry instead of experimentally identified P2/m. The insights gained by this study and the verified ab initio methods for accurate MTT calculations can be applied to fast screen and quantitatively design novel UHT-SMAs having similar properties with desirable MTTs and much reduced cost.

First-principles study of lithium behavior in the ABA-stacking trilayer graphene with defects

To investigate the effect of defects on the Li embedding in graphene, we have studied the embedding and migration of Li in graphene with single-vacancy (SV), double-vacancy (DV), and Stone-Wales (SW) defects using the first-principles calculations. The results show that Li atom prefers to embed in regions with defect, and the presence of defect enhances the Li embedding in graphene. From the perspective of solution energy, Li embedded in the defect region of SV is the most stable, followed by the defect region of DV and SW. Migration results reveal that defects lead to an increase in the energy barrier for Li atom migration between layers and that Li is likely to be trapped in the defect region during migration. Open-circuit voltage and theoretical capacity calculations demonstrate that the lithium capacity of the ABA-stacking trilayer perfect graphene is 248 mAh/g. The lithium capacity diminishes to 165 mAh/g when a SW defect is present in the ABA-stacking trilayer graphene. In contrast, the lithium capacity increases to 270 mAh/g and 292 mAh/g when SV or DV defect is present in the ABA-stacking trilayer graphene, respectively. It is sufficient to show that graphene with low-density SW defect is unsuitable for application as electrode materials. Conversely, the low density of SV and DV defects can increase the lithium capacity of the ABA-stacking trilayer graphene at the same time, which will also lead to lithium deposition to some extent.

First-principles study of electronic, mechanical, and optical properties of M3GaB2 (M = Ti, Hf) MAX phases

Integrating ceramic and metallic properties in MAX phases makes them highly desirable for diverse technological applications. In this study, through first-principles density functional theory (DFT), we investigated the physical properties of two new 312 MAX compounds, M3GaB2 (M = Ti, Hf). Chemical stability is confirmed via formation energy assessment, while mechanical stability is established by determining elastic stiffness constants. A thorough analysis of mechanical behaviors includes bulk modulus, shear modulus, Young's modulus, and hardness parameters. M3GaB2 demonstrates elastic constants and moduli closely aligned with other 312 carbides. Understanding the electronic band structure and density of states (DOS) sheds light on metallic properties, with anisotropy in electrical conductivity clarified through energy dispersion analysis. Investigation of photon interaction with titled compounds, including dielectric constants (real and imaginary parts), refractive index, absorption coefficient, photoconductivity, reflectivity, and energy loss function, has been carried out. The potential of M3GaB2 borides as a coating to reduce solar is evaluated based on the reflectivity spectra. These findings deepen our understanding of material properties and suggest diverse applications for M3GaB2 in various technological domains.

Predicting the electronic, optical, and thermometric properties of novel K2LiSbX6 (X = Cl, Br, I) semiconductors: A first-principles study

Due to their acceptable optical absorption efficiency, greater stability, adjustable bandgap, huge carrier mobility, non-toxicity, readily accessible raw materials, and low cost. The halide-based double perovskites (DPs) have demonstrated several advantages over halide-based perovskites. The Perdew-Burke-Ernzerhof (PBE) functional is used to compute the electrical, optical, mechanical, and thermal properties of halide-based DPs K2LiSbX6 (X = Cl, Br, I) in the Generalized Gradient approximation (GGA) framework of density functional theory (DFT). The objective of studying these materials is to compute the electronic, optical, and thermal properties, to use these materials in the solar cell and thermal applications. It is calculated what the structural parameters are, including the lattice parameter, cell volume, total energy, bulk modulus, pressure derivative, and tolerance factor. The compound’s semiconducting nature is revealed by the electrical density of states, and the band structure shows that the band gaps (3.7 eV, 2.9 eV, and 2.2 eV) are indirect in nature. To address the under-estimated band gap as found in the GGA-PBE functional, the mBJ functional is introduced. Electronic structures analysis and provide explanations for the actual and fictitious parts of the dielectric function ε (ω), absorption coefficient α(ω), energy loss function L(ω), reflectivity ℜ(ω), refractive index n (ω), and extinction coefficient K (ω) versus photon energy (eV). According to these criteria, Br, Cl, I-based materials are optically preferable to K-based compounds. Because of the above predicted outcomes, we conclude that these materials are good candidates for optoelectronics and thermal devices.

Synergistic effect of lithium ions for fast diffusion in Li2ZrCl6 solid electrolytes

Rare-earth metal-free Li2ZrCl6 has recently attracted much attention as a promising solid electrolyte for all-solid-state batteries due to its cost-effectiveness. This first-principles study using van der Waals correction clarifies the Li diffusion mechanism in trigonal α- and monoclinic β-Li2ZrCl6. In the most stable α- and β-Li2ZrCl6 structures obtained from systematic investigations, Li and Zr ions prefer to exist in the same layer, forming two-dimensional Zr/Li layers with Li ions interspersed between ZrCl6 octahedra. When Li ions diffuse in α- and β-Li2ZrCl6, they escape from the Zr/Li layer along the out-of-plane direction and move to the Zr-free layer, where they diffuse freely along the in-plane direction. Thus, Li diffusion in Li2ZrCl6 is characterized by interlayer diffusion between the Zr/Li and Li layers followed by intralayer diffusion in the Li layer. The interlayer/intralayer diffusion, resulting in the highest conductivity of 5.4 × 10−5 S cm−1 for α-Li2ZrCl6, is enabled by a synergistic effect of two Li ions, where one Li ion already present in the Li layer promotes the other adjacent Li ion to escape from the Zr/Li layer. Individual Li ions vibrate at the stable octahedral site for a long time and then quickly jump to another octahedral site via the intermediate tetrahedral site, which is identified as the atomic-scale Li jump process in Li2ZrCl6.

The first-principles study of 2D monolayer T-Mo2C as promising anode material for Lithium-ion Batteries

The growing demand for renewable energy technologies emphasizes the necessity for advancements in anode materials to enhance the performance of lithium-ion batteries (LIBs). In this research, we employ first-principles calculations to investigate the properties of a T-Mo2C monolayer proposed as an anode material. Phonon dispersion calculations and ab initio molecular dynamics (AIMD) simulations are conducted to assess the dynamical stability and thermal characteristics of the T-Mo2C monolayer as an anode material. Remarkably low diffusion barriers of 0.029 eV (Li) and 0.01 eV (Na and K) have been identified, facilitating rapid ion mobility. Furthermore, a monolayer of metal ions (M = Li, Na, K) absorbed onto T-Mo2C is explored, revealing a high specific capacity of approximately 1314.37 mAh/g (Li), 262.87 mAh/g (Na), and 32.85 mAh/g (K). The average open circuit voltage is determined to be 0.08 V (Li), 0.68 V (Na), and 2.59 V (K). This research provides a comprehensive overview of T-Mo2C monolayer as a high-capacity anode material, emphasizing its significant contributions to advancing energy storage systems, particularly in the context of LIBs. The findings presented here pave the way for the development of efficient and sustainable energy storage solutions to meet the escalating demands of the renewable energy landscape.

The effect of doping/dual-doping with nitrogen and silicon on the structural, electronic, and optical properties of graphene: first-principles study

The effect of doping/dual-doping with nitrogen and silicon on the structural, electronic, and optical properties of graphene: first-principles study

Beryllium-doped biphenylene network: A first-principles study

The controlled modification of material properties through doping has garnered significant interest in materials science research. In this paper, employing first principles calculations, we systematically investigate the doping of beryllium (Be) atoms into the biphenylene network (BP) for the first time. Two doping concentrations, 0.04 (minimum) and 0.17 (maximum), along with two distinct substitution sites, are considered, denoted as Bex-BP-Cy (x = 0.04, 0.17; y = 1, 2). Our results reveal that both Bex-BP-Cy (x = 0.04; y = 1, 2) and Bex-BP-C2 (x = 0.17) exhibit favorable thermodynamic stability. At lower concentrations, they retain metallic properties, while at higher concentrations, Bex-BP-C2 (x = 0.17) is a P-type indirect semi-conductor with a narrow band gap of 0.42 eV using PBE functional and a band gap of 1.72 eV with the HSE functional. The mechanical properties of Be-doped BP display notable anisotropy, indicative of excellent mechanical stability. Furthermore, compared to pristine BP, the absorption capacity of Bex-BP-C2 (x = 0.17) along the x direction in the visible region is significantly enhanced. Our study highlights the effective modulation of the electronic, optical, and mechanical properties of BP through Be atom doping, providing a novel strategy for the design of advanced materials.

Tailoring structural and optical properties of ZnO system through elemental Mn Doping through First-principles calculations

In this study, band structure and optical properties of Manganese (Mn) doped ZnO are investigated adopting first-principles study calculations. It is observed that, by addition of Mn in ZnO crystal, the electrical properties like conductivity and dielectric function of material have been improved. The elastic constants for the elements are also calculated which shows that the element is stable after addition of dopant. The computational study is done on CASTEP and Material Studio. The ZnO system is simulated and atoms of Mn has been added replacing Zn atoms. The properties that studied are band structure and optics including conductivity, reflectivity, dielectric function, absorption and refractive index. Furthermore, this study also includes calculation of Elastic constants, XRD Spectra, Phonon dispersion and Temperature profile of doped ZnO systems. The computational study produced promising results and experimental approach can be adopted to reinforce the outcomes of this study.

Gas adsorption on activated AlGaN photocathode: A first-principle study on charge redistribution, work function variation and emission performance attenuation

AlGaN photocathode has important applications in photoelectronic imaging and vacuum electronic devices. However, The short lifetime of the photocathode results in higher costs of usage. This can be attributed to the decrease in vacuum degree and the adsorption of residual gases. In this study, first-principle study and transmission matrix are utilized to investigate five gases (H2O, CO, CO2, H2, CH4) adsorbed on Cs-activated AlGaN (100) surface. Results suggest that all these five gases are prior to deposit on the surface at low coverage of 0.25 ML with adsorption energy of -2 eV. CO has the highest adsorption possibility with its adsorption energy lower than 0 eV. Significant charge transfer occurs at Cs-gas interface, particularly near the oxygen atoms of oxygen-containing molecules. CO2 and CO exhibit a noticeable increase in work function. The increase in the work function of the H2O adsorption is primarily due to its longer dipole length rather than dipole charge by analysing the surface dipole moment. CH4 and H2 have negligible impact on surface properties. Upon gas adsorption, the electrons on the AlGaN surface flow back to the adatoms, causing the CBM shift towards higher energy and upwards band bending. Combined with the surface electron affinity, the iteration of band structures further explains the increase of work function. The open energy of free electron escaping into the vacuum after CO2 adsorption increases to the level of inactivated surface of 5.55 eV from PBE-D2. This study reveals the mechanism of performance decay of the photocathode and is expected to guide the optimization of packaging technology.

A First-Principles Study of 2D Bi-Based BiOClBr, BiOClI, and BiOBrI Monolayers with Ultralow Lattice Thermal Conductivities for Thermoelectric Application

A First-Principles Study of 2D Bi-Based BiOClBr, BiOClI, and BiOBrI Monolayers with Ultralow Lattice Thermal Conductivities for Thermoelectric Application

First-principles study of Stone–Wales defects in monolayer and Bernal-stacked hexagonal boron nitride

Recently, Stone–Wales (SW) defects gradually attracted people’s research interest because of their unique properties. The theoretical research indicated that the SW defect in hexagonal boron nitride (h-BN) can lead to new defect levels in bandgap, making h-BN apply in ultraviolet emitters. However, the SW defect is always observed in graphene and rarely observed in h-BN in the experiments. Here, we confirmed the SW defects are not easily formed in h-BN under thermodynamic conditions by first-principles calculations. Specifically, the monolayer h-BN with SW defect (h-BN-SW) has the weak bond strength, dynamic stability and high-temperature thermal stability, facilitating the healing of SW defects under high-temperature conditions and the role of hydrogen. Additionally, we found the SW defect in AB stacked h-BN (AB-h-BN) have good mechanical stability, dynamic stability and thermodynamic stability than h-BN-SW, especially for AB-h-BN-2SW (2SW defects formed in upper and lower layer of AB-h-BN, respectively), which can meet the requirements for its application in electronic devices. Even under thermodynamic conditions, the formation of SW defects is extremely challenging. Electron beam irradiation technology provides a window for the generation of SW defects in h-BN. This offers opportunities for the introduction and control of SW defects, while also creating potential for their application in electronic devices. Moreover, we found that the absorption peak broadens, and a new absorption peak appears with the generation of SW defects, which is mainly induced by the decrease of bandgap and the generation of defect levels. Our research can provide theoretical guidance at atomic scale for designing and applying h-BN with SW defect in the experiments.