First-principles Calculation Method Research Articles

Theoretical study on arsenene as anode material for magnesium ion battery in rail transit

Abstract The development and regulation of high-performance anode materials contribute to the rapid development of ion batteries in rail transit. In this paper, based on the first-principles calculation method of density functional theory, the properties of two-dimensional arsenene materials are regulated by torsional deformation, and the feasibility of torsionally deformed arsenene as an electrode material for magnesium ion batteries is studied. The results show that the arsenene monolayer remains stable after being adsorbed by a single Mg ion. The properties of arsenene are indirect bandgap semiconductors with a band gap of 1.60 eV. In the current research scope, deformation does not change the semiconductor properties of intrinsic arsenene. As the torsion angle increases, the band gap gradually decreases. The Mg-adsorbed arsenene system exhibits quasi-metallic properties with a band gap of 0.07 eV. The torsional deformation transforms the adsorption system into a small band gap semiconductor. The torsion deformation makes the diffusion energy barrier of magnesium ions on the arsenene monolayer only 0.09 eV, which ensures an excellent charge-discharge rate. The research results provide a theoretical basis for the design of magnesium ion batteries in rail transit.

The role of oxygen in the growth of silver nanowires using the polyol method

Silver nanowires (Ag NWs) are gaining significant interest as a promising material for applications in flexible electronics. However, the growth mechanism of Ag NWs, particularly during the polyol synthesis process, remains unclear due to the complex reduction pathways of ethylene glycol (EG). In this paper, first-principles calculation method was employed to investigate the influence of oxygen during the growth of Ag NWs. Specifically, oxygen affects the decomposition products of ethylene glycol and thus the reducibility of EG. This research aims to reveal the mechanism of oxygen promoting the growth of Ag NWs.

Study of bond strength and electronic properties at the 6H-SiC/Al interface: Based on first-principles calculations

As the medium between the reinforcement and the matrix, the interface plays a critical role in the mechanical properties of silicon carbide particle reinforced aluminum matrix composites. This study used first-principles calculation methods to systematically analyze 14 different 6H-SiC/Al low-index interfaces, including atomic configuration, interface bonding strength, and electronic structure and bonding principles between interfaces. The adhesion work calculations reveal that the C-top-SiC(0001)/Al (111) and SiC(0001)/Al (100) interfaces have larger adhesion work values, specifically 5.09 J/m2 and 5.021 J/m2, respectively. Additionally, the rigid tensile testing confirms that the tensile stress values at the interfaces of C-top-SiC(0001)/Al (111) and SiC(0001)/Al (100) are higher, measuring 36.4 GPa and 32.5 GPa, respectively. The above results show that the interface bonding strength of these two configurations is the highest, the most stable, and most likely to appear in the 6H-SiC/Al interface configuration. The results of the analysis on charge density difference and partial density of states indicate that the interfaces of C-top-SiC (0001)/Al (111) and SiC (0001)/Al (100) are primarily composed of strong ionic and covalent bonds.

First-principles study on thermal transport properties of GaN under different cross-plane strain

With the development of power devices towards high integration and power, the electrical and thermal stresses per unit area become more concentrated and intensified. The impact of cross-plane strain resulting from inverse piezoelectric effect and thermal expansion on power devices cannot be ignored. Cross-plane strain has a substantial influence on the thermal properties of GaN. However, the research on the influence of cross-plane strain on the thermal conductivity of GaN has not been reported in the literature. Based on the first-principles calculation method and the phonon Boltzmann transport equation, the influence of cross-plane strain on the thermal conductivity and phonon characteristics of the GaN lattice is systematically studied in this study. The thermal conductivity of GaN has anisotropy and increases significantly with the decrease in temperature. The thermal conductivity of GaN at room temperature under the free state is calculated to be 257 and 275 W/(m·K) for in-plane (k⊥) and cross-plane (k∥) directions, respectively. Compared with previous theoretical reports, our calculation results are more consistent with the existing experiment values. Under the state of cross-plane strain, the lattice thermal conductivity changes remarkably. In detail, the average thermal conductivity at room temperature decreased by 35 % under a 5 % cross-plane tensile strain state, while it increased by 11.5 % under a 5 % cross-plane compressive strain state. According to the calculation results, the influence of cross-plane on lattice thermal conductivity is mainly due to the change in phonon lifetime. The analysis of two mechanisms of phonon lifetime suppression indicates that the cross-plane strain will significantly change the frequency of the high-frequency optical acoustic branch. This result leads to a change in the phonon scattering process and thus affects the phonon lifetime. Besides, the anisotropy of thermal conductivity changes under different strain values, which may be due to the weakened piezoelectric polarization effect induced by strain.

Melt growth of crystalline α-SrSi2 by the vertical Bridgman method and its thermoelectric characteristics

As a candidate thermoelectric material operating in the low-temperature regime (room temperature to 473 K), we have examined α-SrSi2: a narrow bandgap semiconductor material, which is composed of environmentally benign elements. We are able to report the successful production of single-crystalline-like α-SrSi2 with clear semiconducting properties by melting synthesis, a thermodynamically stable and thermally equilibrium process that reduces unexpected process contamination and improves crystallinity.The crystals up to 20 × 20 × 5 mm3 have been obtained for a solid–liquid phase reaction temperature of 1308 K for 10 h with a growth rate averaging at 0.617 K/h in the temperature range from 1403 K to 1373 K. The band gap of this material was measured at 48 meV, which is higher than the values previously reported. The power factor was measured at 2.9 mW/mK2 at 300 K, which is the highest value ever reported for undoped α-SrSi2.Based on the experimental bandgap values, the hybrid functional was used to correct the first-principles calculation method, and the Seebeck coefficient obtained from the first-principles calculation was compared with experimental values. Which values showed good agreement with experimental values.

Atomic-scale tribological behavior of pressure-induced MoO3(0 1 0)/Ag(1 1 1) heterogeneous sliding interface

The atomic-scale tribological properties of the MoO3(010)/Ag(111) heterogeneous sliding interface were studied by first-principles calculation method. The interface binding energy, sliding potential energy, friction force, charge density difference, partial density of states, Mulliken bond population and HiRshfeld charge were analyzed, and the essence of the friction was revealed. The results show that the sliding potential energy and friction exhibit anisotropy for the pressure-induced MoO3(010)/Ag(111) heterogeneous sliding interface. The friction force can be described by the change of the sliding potential energy, and the charge redistribution between interface atoms is the intrinsic reason for the change of tribological properties. This work provides atomic and electronic level insights for understanding the tribological characteristics between two-dimensional materials and soft metals.

First-Principles Calculations of TiB4 and TiB5 as Anodes with High Capacity for Na-Ion Batteries.

The electrochemical properties of TiB4 and TiB5 monolayers in Na-ion batteries (NIBs) were studied by using the first-principles calculation method based on density functional theory. The TiB4/TiB5 monolayer showed excellent Na storage capacity, capable of adsorbing two layers of Na with theoretical capacities of 1176.77 and 1052.05 mA g-1, respectively. The average operating voltages of the TiB4 and TiB5 monolayers are 0.073 and 0.042 eV, respectively, indicating that they can be used as anode materials for NIBs. More interestingly, the exposed B surface not only brings a high theoretical capacity but also provides a relatively small diffusion barrier of 0.16 (for TiB4) and 0.33 eV (for TiB5), enhancing their rate capability in NIBs.

First-principles calculations of the electronic structure and thermodynamic properties of B–Co–O materials

In the present study, the structural properties, electronic, elastic, and thermodynamic properties of Co4B6O13、Co2B2O5、Co3(BO3)2、Co(BO2)2, and CoB4O7 materials were calculated by adopting first-principles calculation method based on density functional theory. The simulated lattice constant is compliant with the existing experimental data well. The formation energy, Gibbs free energy, and phonon dispersion curves show that the B–Co–O materials are thermodynamically stable. The results show that the mechanical properties of CoB4O7 material is excellent, while the mechanical properties of Co2B2O5 material is the weakest. The CoB4O7 material has higher Debye temperature and constant volume heat capacity, and the thermodynamic stability of Co3(BO3)2 is the best. By analyzing band structure and electronic density of states, Co2B2O5 and Co3(BO3)2 materials are conductors, Co4B6O13, Co(BO2)2 and CoB4O7 materials belong to P-type semiconductors. Through electronic density of states analysis and Hirshfeld analysis, they indicated that five B–Co–O materials exhibit ferromagnetic.

Efficient visible-light-driven photocatalytic hydrogen evolution in novel type-II SnS2/Al2S2 van der Waals heterostructures

With the exacerbation of environmental pollution and the energy crisis, the development and design of environmentally friendly and efficient photocatalytic catalysts for water splitting with visible light have become particularly imperative. This study delves into the detailed investigation of the novel type-II van der Waals heterostructure of SnS2/Al2S2 utilizing first-principles calculation methods. By leveraging the advantages of indirect type-II band alignment and high carrier mobility, the efficient separation of electron-hole pairs is achieved, thereby facilitating enhanced participation of electrons and holes in photocatalytic reactions. Furthermore, the heterostructure manifests a peak optical absorption coefficient value of approximately 5.34×104 cm−1 in the visible light spectrum, accompanied by the occurrence of red-shifting, which fosters efficient absorption of visible light. It is noteworthy that under conditions of pH = 0–3.7, the heterojunction surpasses the redox potential of water splitting, concurrently displaying a substantial hydrogen evolution reaction (HER) and a high efficiency of converting sunlight to hydrogen (22.31 %). These results underscore the promising potential of the SnS2/Al2S2 heterostructure as a photocatalyst for water splitting, offering crucial theoretical support and practical guidance for the further advancement of hydrogen production via water splitting technology.

Thermal Transport Properties of Two-Dimensional Janus MoXSiN2 (X = S, Se, and Te).

The design of Janus materials offers an effective means of regulating both their physical and chemical properties, leading to their application in various fields. However, the underlying mechanism governing the modulation of the thermal transport characteristics through the construction of Janus materials remains unclear. In this work, we introduce VI-group elements into the MoSi2N4 structure, yielding two-dimensional Janus MoXSiN2 (X = S, Se, and Te) and systematically investigate their thermal transport properties based on first-principles calculation methods. Our findings reveal that the lattice thermal conductivities (κl) of MoSSiN2, MoSeSiN2, and MoTeSiN2 are 47.2, 24.3, and 40.6 W/mK at 300 K, respectively, significantly lower than that of MoSi2N4 (224 W/mK). Such low κl values mainly come from the introduction of X atoms, which enhances phonon scattering and reduces phonon vibration frequencies. In addition, MoTeSiN2 exhibits a higher κl compared to MoSeSiN2, contrary to the trend observed in most materials containing VI-group elements, where κl decreases gradually from S to Te. This anomalous behavior can be attributed to the competitive result between its lower phonon vibrational frequency and weaker phonon anharmonicity of MoTeSiN2. This work elucidates the inherent mechanism governing the modulation of thermal transport properties in Janus materials, thereby enhancing the potential application of Janus MoXSiN2 in engineering thermal management.

Effect of solutes segregation in a binary TiAl alloy: A first-principles calculation method

Comprehending the interfacial structures and energetics of interfaces between γ-TiAl and α2-Ti3Al phase is critical to understanding the stabilities of the binary-phase TiAl-Ti3Al alloy. Here a comprehensive first-principles investigation is reported on the structures and energetic properties of γ-TiAl(111)/α2-Ti3Al(0001) interfaces with 19 segregated transition metals considered. The results indicate that all considered atoms have a tendency to segregate at the interface. The interfacial strength enhancement occurs after V, Cr, Mn, Fe, Nb, Mo, Tc, Ru segregated in TiAl, Ag segregated in Ti3Al, and almost all solute atoms can improve interface stability. Compared with the pure interface, the bonding between the segregated atoms and the surrounding atoms is stronger at the interface after V or Nb segregation, while the bonding between Cd and the surrounding atoms is weaker. Our calculations provide the necessary interfacial structures and energetics for predicting the stabilities of binary TiAl alloy.

Effect of non-metal doping on the optoelectronic properties of ZrS2/ZrSe2 heterostructure under strain: a first-principles study.

In this paper, we systematically studied the effects of non-metallic element (B, C, N, O, F) doping and biaxial stretching on the photoelectric properties of ZrS2/ZrSe2 heterostructures by using the first-principles calculation method based on density functional theory. The results show that the p-type doping is realized by B, C, and N atom doping, and the n-type doping is realized by O and F atom doping. The doping of B and C atoms produces impurity energy levels in the band gap, which affects the conductivity of the heterostructure. The band gap of N and O atom-doped heterostructures increases under tensile strain, but it is still a direct band gap. The analysis of the optical properties of the heterostructures shows that the doping of non-metallic atoms can adjust the optical absorption rate and reflectivity of the heterostructures. Under the action of tensile strain, the optical properties of the doped heterostructures have changed significantly in the low-energy region. This article provides a theoretical basis for the future application of ZrS2/ZrSe2 heterostructures. This paper uses the first-principles calculation method based on density functional theory. The PBE exchange-correlation functional based on generalized gradient approximation (GGA) is selected for the specific calculation, and the crystal structure is geometrically optimized by the ultrasoft pseudopotential method. It is verified that when the cutoff energy of the ZrS2/ZrSe2 heterostructure is 500 eV, the K-point grid is selected to be 10 × 10 × 2 with the lowest energy, so the cutoff energy is selected to be 500 eV. The K-point grid is selected to be 10 × 10 × 2. The convergence limits for structural optimization are as follows: the maximum force between atoms is 0.01 eV/Å, the convergence threshold of the maximum energy change is set to 10-9 eV/atom, and the convergence threshold of the maximum displacement is 0.001 Å. In order to avoid the influence of atomic periodic motion between different atomic layers, a vacuum layer of 20 Å is added in the vertical direction. Considering the interaction of vdW between the interfaces, the DFT-D2 method is used to verify. The optical properties were calculated by the random phase approximation method, and the K-point grid was selected as 12 × 12 × 2.

First principles investigation of in-situ NiAl(110)/Ag(111) and NiAl(110)/MoO3(010) heterogeneous interfaces behavior in composite coatings

The interface properties of in-situ NiAl(110)/Ag(111) and NiAl(110)/MoO3(010) heterogeneous interfaces were systematically studied by first-principles calculation method. The interfacial adhesion work, interfacial energy, Mulliken bond population and partial density of states were analyzed, and the bonding mechanism were revealed from the atomic and electronic perspective. The results show that the NiAl(110)/Ag(111) heterogeneous interfaces with OB-NiAl stacking site and the NiAl(110)/MoO3(010) heterogeneous interfaces with OT-Al stacking site are the most stable interface structures with maximum interfacial adhesion work (1.602 J/m2 and 2.833 J/m2, respectively) and minimum interfacial energy (0.7391 J/m2 and −0.8154∼0.7796 J/m2, respectively). Furthermore, charge density differences, partial density of states and Mulliken bond population analysis indicates that the interface bonding mechanism of NiAl (110)/Ag(111) heterogeneous interface is dominated by Al-Ag covalent bonds, and the bonding mechanism of NiAl(110)/MoO3(010) heterogeneous interface is mainly the combination of Al-O ionic bonds and Al-Mo covalent bonds.

Tunable electronic structure and optical properties of GaN monolayer via substituted doping and strain

In this study, the stability, optical properties and electronic structure of transition metal (TM) (Cr, Mn, Fe) doped GaN monolayers is investigated within the first-principles calculation methods. Additionally, the influence of biaxial strain on the aforementioned system is explored. The results demonstrate that substitutional doping effectively adjusts the electronic structure of GaN monolayer, enhancing its performance. The TM-doped GaN monolayer structures exhibit strong dynamic stability: doping with Cr and Fe bring magnetic properties, while Mn doping results in a half-metallicity property. In terms of optical absorption, the GaN:Mn system exhibits significant absorption in the infrared region, while GaN:Cr and GaN:Fe systems show stronger absorption in the visible light and ultraviolet regions compared to the pristine GaN monolayer. Under the biaxial strain from −3% to +12%, with increments of 3%, the band gap types of GaN:Cr, GaN:Fe, and GaN:Mn systems undergo minimal changes, with gradual reduction in gap values. Meanwhile, the optical absorption of doped systems exhibits systematic growth and redshift, particularly evident in the infrared-visible-ultraviolet spectral regions for the GaN:Mn system. These results indicate the controllability and variability of two-dimensional GaN materials, providing new avenues for the potential use of GaN as a material for optoelectronic devices.

First-principles study on Ga interactions with Pu surfaces and [formula omitted]-Pu bulk

The Ga-Pu alloy presents a potential solution to address the constraints of Pu metal as a fuel. Therefore, it is imperative to investigate its pertinent properties. In research, surface models were commonly employed for the preliminary exploration of information, including the identification of more stable binding sites. First-principles calculation methods were employed to investigate the adsorption characteristics of Ga atoms at various sites on the surfaces of Pu(100), Pu(110), and Pu(111), as well as their binding behavior within the Plutonium unit cells. The analysis, by adsorption energies, Charge Density Difference, Bader Charge, Electron Localization Function (ELF), Reduced Density Gradient (RDG), and Projected Density of States (PDOS), revealed that when Ga atoms interacted with the surface, they tended to bind more strongly to the Pu(100) long-bridge and Pu(110) TOP 1 sites, with adsorption energies of -2.585eV and -3.150eV, respectively. On the Pu(111) surface, the adsorption energies at the three sites were adsorption comparable, and the binding trends were similar. Upon entering the δ-Pu unit cells, Ga atoms formed a more stable structure after combining at the G, H, and I sites. The stability both on the surfaces and within the δ-Pu unit cells was primarily attributed to metallic bonds, with an additional contribution from mutual attraction due to van der Waals forces in surface adsorption. The adsorption behavior of Ga on the Pu surface and its binding within the δ-Pu unit cell was systematically investigated. This exploration aimed to offer ideas and insights for a comprehensive understanding of Ga-Pu alloys in subsequent studies.

Strain-induced modification in thermal properties of monolayer 1T-ZrS2 and ZrS2/ZrSe2 heterojunction.

This paper systematically analyzes the phonon dispersion curves of single-layer ZrS2, ZrSe2, and ZrS2/ZrSe2 heterostructures under different strains. The phonon spectra and thermal parameters of the three structures were obtained based on the density functional perturbation theory method. The upper limits of strain that different monolayers and heterojunctions can withstand were studied. The monolayers ZrSe2 and ZrS2 can withstand up to 8% biaxial tensile strain, and the ZrS2/ZrSe2 heterojunction can withstand up to 6% biaxial tensile strain. In addition, the van der Waals force of the heterojunction may cause phonon tearing in the vertical direction. The application of biaxial tensile strain can adjust the thermal properties of the system to a large extent, which is similar to the strain effect in the pristine case. When the temperature rises, the entropy enthalpy of the three structures also gradually increases, the free energy gradually decreases, and the heat capacity of the system gradually increases until it tends to be stable. Taking single-layer ZrS2 as an example, we analyzed the change curve of thermal properties of single-layer ZrS2 under tensile strain. The results show that with the gradual increase of strain, the crystal's entropy, enthalpy, and free energy change differently. In addition, the heat capacity increases slowly under high temperatures. When all systems reach the limit strain, the phonon spectrum appears to have an imaginary frequency, and the thermal properties decrease significantly. This paper uses the first-principle calculation method based on density functional theory, and the PBE exchange-correlation function based on generalized gradient approximation (GGA) is selected for a specific calculation. The density functional perturbation theory (DFPT) calculates the full kinetic matrix. Because the lattice constants of ZrS2 and ZrSe2 are similar and have similar periodicity, the corresponding unit cells are used for structural optimization and property calculation. The Brillouin zone is integrated using the K points generated by the Monkhorst-pack method. For single-layers ZrS2 and ZrSe2, 8 × 8 × 1K-point grid is selected, and for ZrS2/ZrSe2 heterojunction, 8 × 8 × 2K-point grid is selected. A vacuum layer of 30Å was added in the vertical direction to avoid interlayer interaction. The non-conservative pseudopotential method is used to optimize the structure, and the optimization convergence is set as follows: the cutoff energy is set to 700eV, the convergence threshold of the maximum force between atoms is 0.01eV/Å, the convergence threshold of the maximum energy change is set to 1 × 10-9eV, and the convergence threshold of the maximum displacement is 0.001Å.

Enhancement of interfacial thermal conductance by introducing carbon vacancy at the Cu/diamond interface

Effective heat dissipation of semiconductor devices is crucial for their extended lifespan and operational stability, and the interface of semiconductors provides an effective window for thermal design and management. In this work, we have systematically investigated the effect of the carbon vacancy on the thermal conductivity of diamond and the interface thermal conductance (ITC) of Cu/diamond by using both first-principles calculation and molecular dynamics methods. Although the carbon vacancy leads to a decrease in the thermal conductivity of diamond, a marked increase in ITC from 37.98 MWm−2K−1 to about 177 MWm−2K−1 for diamond (1 1 1) plane and from 78.8 MWm−2K−1 to about 241 MWm−2K−1 for diamond (0 0 1) plane is observed between Cu and diamond with carbon vacancy. The increase of the ITC is mainly due to the anharmonic phonon scattering, revealed by the phonon density of states and phonon participation ratio.

Coexistence of Ferromagnetism and Ferroelectricity in Cu-Intercalated Bilayer CrI3.

Design of two-dimensional (2D) multiferroic materials with two or more ferroic orders in one structure is highly desired in view of the development of next-generation electronic devices. Unfortunately, experimental or theoretical discovery of 2D intrinsic multiferroic materials is rare. Using first-principles calculation methods, we report the realization of multiferroics that couple ferromagnetism and ferroelectricity by intercalating Cu atoms in bilayer CrI3, Cux@bi-CrI3 (x = 0.03, 0.06, and 0.25). Our results show that the intercalation of Cu atoms leads to the inversion symmetry breaking of bilayer CrI3 and produces intercalation density-dependent out-of-plane electric polarization, around 18.84-90.31 pC·cm-2. Moreover, the switch barriers of Cux@bi-CrI3 in both polarization states are small, ranging from 0.31 to 0.69 eV. Furthermore, the magnetoelectric coupling properties of Cux@bi-CrI3 can be modulated via varying the metal ion intercalation density, and half-metal to semiconductor transition can be occurred by decreasing the intercalation density of metal ions. Our work paves a practical path for 2D magnetoelectron coupling devices.

Theoretical investigation of the effect of mole fraction on the electronic and optical properties of a binary armchair antimonene−phosphorene nanoribbon

In this work, the electronic and optical properties of a binary armchair antimonene-phosphorene nanoribbon have been studied with a variation of the P mole fraction by first-principles calculation method based on density functional theory. The calculated cohesive energy shows that the stability of the binary SbP nanoribbon increases by increasing the molar fraction of phosphorus to 100%. We have demonstrated that the band gap of SbP nanoribbons can be modified by applying different mole fractions. The band gap value of SbP nanoribbon increases firstly up to mole fractions of approximately 50% and decreases up to 80% and then increases. A direct-to-indirect and an indirect-to-direct gap transitions occur at 5 to 75% (except for 35%) and 80 to 100% mole fractions, respectively. The optical properties of the mentioned structures with different mole fractions are analyzed, and it is found that the optical properties of binary SbP nanoribbons changed by P mole fraction; and also, the light absorption peak is mainly concentrated in the ultraviolet region. Compared with the pure antimonene, the light absorption is significantly enhanced after increasing the mole fraction of phosphorus to 100%. From a theoretical point of view, our results can offer promising applications in electronic and optical nanodevices.

Origin of the Nonmonotonic Pressure Dependence of the Band Gap in the Orthorhombic Perovskite CsPbBr3.

The perovskite CsPbBr3 exhibits an unusual nonmonotonic dependence of the band gap on increasing pressure to about 2.0 GPa as compared to conventional semiconductors. Using the first-principles calculation method, we show that under pressure, isotropic volume deformation induces considerable compression of the Pb-Br bond length and thus an enhanced interaction between atomic orbitals of the antibonding valence band maximum states and the mostly nonbonding conduction band minimum states, resulting in a monotonic decrease in the band gap. On the other hand, structural relaxation tends to reduce the strain energy by decompressing the Pb-Br bond length and simultaneously compressing the Pb-Br-Pb bond angle, which increases the band gap energy. We find that the competition between the volume deformation effect and structural relaxation effect is the origin of the nonmonotonic behavior of the dependence of the band gap on pressure.