Computational Materials Science最新文献

Silicon is the fundamental material for the semiconductor and microelectronics industries, but controlling the electronic band gap structure of diamond-type silicon remains a huge challenge to adapt to growing applications. Here, we have predicated 23 new silicon allotropes in space group P2/m from 279 possible structures by high-throughput screening accompanied by graph and group theory based on random strategy (RG²) code. The mechanical, electronic and optical properties of these structures were studied in detail. These novel silicon allotropes demonstrate various electronic structures, including metal, direct/quasi direct bandgap structure, and indirect bandgap structures. These new silicon allotropes demonstrate various electronic structures, including metal, direct/quasi direct bandgap structure, and indirect bandgap structures. Besides different electronic bandgap structures, all 23 structures exhibit strong absorption in the visible light region and P2/m-15 demonstrates the excellent mechanical properties (Bulk modulus beyond 80 GPa). Based on their nice stability, good mechanical, electronic and optical properties validated by the ab inito molecular dynamics simulation, phonon spectra and density functional theoretical calculations, these predicted silicon allotropes provide not only ideas for the synthesis of new silicon allotropes but also dawn for expanding the application of semiconductor materials.

This research examines the crucial role played by Cr₂₃C₆ carbides in hydrogen trapping and their subsequent impact on the mechanical properties of the material. The hydrogen solution energies at different defect sites within the bulk phase of Cr₂₃C₆ and the Ni/Cr₂₃C₆ interface were analyzed using first-principles computations. This study underscores the notable vulnerability of nickel-based alloys to hydrogen embrittlement as the carbide content increases. Substantial hydrogen enrichment at the Ni/Cr₂₃C₆ interface, particularly at octahedral interstitial sites on the Ni side and C vacancies at the interface, was identified through comprehensive atomistic simulations. This enrichment negatively affects separation at the interface, indicating an increased risk of brittle fracture in the presence of hydrogen. By providing insights into the microscopic processes involved, our results seek to contribute to the development of nickel-based alloys that are more resistant to hydrogen, thereby influencing material selection and treatment in industrial applications prone to hydrogen embrittlement.

Transition Metal Chalcogenide Perovskites (TMCP) have been in the spotlight due to their exceptional optoelectronic properties. ${\mathrm{CaZrS}}_3$ is one among them with an experimental bandgap of 1.90 eV. If its bandgap is tuned to lower values, it can be employed in additional photovoltaic applications, such as solar cell absorbers. In this work, the transition metal element Zr in ${\mathrm{CaZrS}}_3$ is substituted with Ti atoms in different proportions and the optoelectronic properties are investigated using Density Functional Theory (DFT). The optoelectronic calculations are all done using the DFT+U method including the spin–orbit coupling. With substitutional alloying, we successfully tuned the energy gap from 1.91 eV to 1.18 eV and the photovoltaic properties were also observed to be modified. For the substituted ${\mathrm{CaZr}}_{1-x}{\mathrm{Ti}}_x{S}_3$ samples, large birefringence is observed. This indicates enhancement in optical anisotropy via substitutional alloying which is significant in both linear and nonlinear optoelectronic applications like polarizers, wave plates etc.

To explore the formation mechanism of native point defects in high Al content AlGaN film, the first principles methods are applied to study the native point defects in Al_0.5Ga_0.5N. The different kinds of vacancies, interstitials, and antisites are investigated. The formation energies of Al_0.5Ga_0.5N with native point defects under different charge states and growth conditions are analyzed and compared. Then, the preferable charge state, donor and acceptor properties of Al_0.5Ga_0.5N with different native point defects are explicitly obtained. The results show that Al_N, Ga_N, Al_i, and V_N exhibit donor properties in p-type condition while V_Ga, V_Al, V_N, and N_Ga exhibit acceptor properties and can play roles as compensating center in n-type Al_0.5Ga_0.5N under metal rich condition. For N rich condition,V_Ga, V_Al, N_Ga, and N_Al are favorable acceptors in n-type Al_0.5Ga_0.5N. Meanwhile, the charge distribution and bonding state of Al_0.5Ga_0.5N with native point defects are explored. It is found the N atoms in N_i and N_Ga form covalent bond and ionic bond with atoms in Al_0.5Ga_0.5N. Moreover, the band calculation reveals that the removal of N atom in Al_0.5Ga_0.5N makes the conduction band fatter and the effective masses of electrons increase while the introduction of N point defects make the valence band flatter, increasing the effective masses of holes. Furthermore, the corresponding thermodynamic transition energy levels of defects under different charge states are summarized. It is found that the thermodynamic transitions for V_N, N_i, and N_Al may likely to happen under certain conditions. The above studies yield a detailed and quantitative description of native point defects in Al_0.5Ga_0.5N, which helps to get a deeper insight to the growth and doping of AlGaN.

The water in coal causes many negative effects on the processing and utilization of coal. Oxygen-containing functional groups (OFGs) are primary adsorption sites for water molecules on coal surfaces. However, little is known about the adsorption configuration of water clusters on OFGs. In this study, density functional theory (DFT) calculations were used to predict the adsorption configurations of water clusters on –COOH and –OH. The results indicated that water clusters tend to form quadrilateral and cubic shapes on both –COOH and –OH, with quadrilateral water clusters being more stable than cubic water clusters. The cubic water cluster is adsorbed on –COOH through two water molecules that directly form hydrogen bonds with –COOH. In contrast, the cubic water cluster is adsorbed on –OH through a water molecule at one of its vertices. The strong attraction of –COOH to water molecules introduces a minor defect in the cubic water cluster. Because of the synergistic effect of neighboring OFGs on the adsorption of water molecules, the average adsorption energy of water molecules is greater than that of water clusters on a single OFG. These results provide valuable microstructural insights into the adsorption of water on coal.

In-plane Transition Metal Dichalcogenides (TMDs) heterostructures hold immense potential for various applications in the modern semiconductor industry, including electronics, optoelectronics, and photovoltaic devices. Different TMD monolayers can be ‘stitched’ together to construct an in-plane (lateral) heterostructure. As different TMD monolayers present different work functions and have their intrinsic shortcomings, a TMD heterostructure is an excellent form to optimize their properties and to achieve the best functionality. This requires a quantitative understanding of the properties of the interfaces in the heterostructures. In this work, we perform nonequilibrium molecular dynamics simulations, based on a parametrized Stillinger-Weber potential, to investigates the thermal conductance of the interfaces in 2D ${\mathrm{WS}}_2/{\mathrm{MoSe}}_2$ and ${\mathrm{MoS}}_2/{\mathrm{MoSe}}_2$ in-plane heterostructures, as well as in 2D lateral ${\mathrm{WS}}_2/{\mathrm{MoSe}}_2$ superlattices. Three distinct types of interfaces, including defect-free coherent interfaces, interfaces with the $5\mid 7$ defects, and the alloy-like incoherent interfaces, are explored. The effects of interphase structure and temperature are quantified. Phonon density of states (PDOS) analysis is used to understand the effect of different interphase structures. The effect of superlattice period on thermal conductance of the superlattices has also been quantified.

Selecting the best microscope parameters for optimal image quality currently relies on microscopists; there exist no procedures or guidelines for tuning parameters to ensure the desired image quality is achieved. More importantly, for quantitative analysis purposes, adequate image quality for segmentation should be prioritized. This paper is the second of two parts, describing a regression model, mixed input, multiple output with Keras TensorFlow, trained to predict the beam energy and probe current, two important parameters for image quality. Specifically, parameters are predicted to optimize the image quality for segmentation, using a generated training set, as described in Part 1 of this paper. Model performance is then tested on models trained with multiple different training sets, and with different proportions of simulated and acquired data. First, to examine the impact of the training set on the prediction accuracy and then, to evaluate the importance of including real data during training. The model successfully predicted the beam energy and probe current to set on the microscope to improve image quality for segmentation. Models trained with both simulated and acquired data performed the best, as evaluated by their efficacy at improving the image quality for feature segmentation.

Magnetic tunnel junctions (MTJs) constructed from atomically thin two-dimensional (2D) magnetic materials have attracted great attention in recent years because it meets the requirements of miniaturization and high tunability of next-generation spintronic devices. In this work, we demonstrate that the ferromagnetic semiconductor VS${}_2$ is transformed into a half-metal in VS${}_2$/MoSSe vdW heterostructure. Based on the heterostructure, we design an in-plane MTJs that comprise a monolayer VS${}_2$ barrier sandwiched between two VS${}_2$/MoSSe heterostructure electrodes. Through density functional calculations combined with a nonequilibrium Green’s function technique, it is found that the tunnel magnetoresistance (TMR) ratio as high as 4.35 × 10${}^9\text{\%}$ can be achieved. Moreover, the TMR ratio can be tuned by the barrier length, and the maximum value exceeds 10${}^{15}\text{\%}$. These results not only provide a novel route for designing MTJs using 2D ferromagnetic semiconductor material, but also demonstrate the great importance of vdW heterostructures in the design of spintronic devices.

The knowledge of the thermophysical properties of liquid metals and alloys is essential for expanding the materials database and designing materials with good properties. In this work, we developed an interatomic potential using a deep neural network (DNN) algorithm for liquid Ag-Si alloys. Compared with ab initio molecular dynamics (AIMD) results, the DNN potential provided a good description of the information of energy, force, and structure features of the system in the simulated temperature range. Through this potential, we can obtain the thermophysical properties of different compositions of liquid alloys by simulation way. The computed thermophysical properties are in excellent agreement with the reported experimental data. The analysis of local structure indicates that the liquid ordering and stability strengthen upon cooling at the atomic level, eventually leading to an increase in thermophysical properties.

A comparative analysis of the physical properties of Gd₂Zr₂O₇ weberite and pyrochlore is conducted using first-principles methods. The structural characteristics of Gd₂Zr₂O₇ pyrochlore and weberite are examined at the atomic site, local coordination, and lattice parameter levels. The findings from ab initio molecular dynamics simulations and experimental data confirm the existence and stability of the Gd₂Zr₂O₇ weberite structure at 300 K. The formation of cation antisite defects is calculated to be more facile in the weberite lattice compared to pyrochlore. The formation energy of vacancy defects is strongly correlated to the distinct defect configurations. The calculations further highlight that Gd₂Zr₂O₇ weberite exhibits mechanical properties comparable to pyrochlore. The insulating nature, chemical bonding characteristics, and charge states of individual atoms in weberite and pyrochlore are elucidated through analysis of the partial density of states and Bader charges.