Effect of Ti Doping on the Microstructure and Properties of SiCp/Al Composites by Pressureless Infiltration

The effects of Ti doping on the microstructure and properties of SiCp/Al composites fabricated by pressureless infiltration were comprehensively investigated using first-principles calculations and experimental analyses. First-principles calculations revealed that the interface wetting and bonding strength in an Al/SiC system could be significantly enhanced by Ti doping. Subsequently, the Ti element was incorporated into SiC preforms in the form of TiO2 and TiC to verify the influence of Ti doping on the pressureless infiltration performance of SiCp/Al composites. The experimental results demonstrated that the pressureless infiltration of molten Al into SiC preforms was promoted by adding TiC or TiO2 due to the improved wettability. However, incorporating TiO2 leads to the growth of AlN whiskers under a N2 atmosphere, thereby hindering the complete densification of the composites. On the other hand, TiC doping can improve wettability and interface strength without deleterious reactions. As a consequence, the TiC-doped SiCp/Al composites exhibited excellent properties, including a high relative density of 99.4%, a bending strength of 287 ± 18 MPa, and a thermal conductivity of 142 W·m-1·K-1.

First-principles calculation of self-interstitial atom-impurity atom interactions in ferritic steel

In this study, the interactions between self-interstitial atoms (SIA) and impurity atoms (Cu and P) in the body-centered cubic (bcc)-Fe matrix have been investigated using the first principles approach. The results show that Cu and P atoms are more prone to segregation on perpendicular and parallel surfaces containing dumbbell atoms, respectively. Next, by combining the charge density difference and considering the electronic structure and lattice distortion, the origin of the binding energy of complexes formed between SIA and impurity atoms was discussed. The results show that as the number of impurity atoms increases, the atomic bonds formed by the interactions between the impurity atoms decrease the binding energy between single impurity atoms and the matrix and reduce the strain field around them, resulting in an increase in the stability of the complexes. Comparison with previous experimental results revealed the reasons for the changes in atomic occupancy during the segregation of Cu and P atoms. The results provide insights into the behavior of impurity atoms in irradiated materials and provide a deeper understanding of the electron level of impurity atomization.

Engineering Layertronics in Two-Dimensional Ferromagnetic Multiferroic Lattice

Layertronics, rooted in the layer Hall effect (LHE), is an emerging fundamental phenomenon in condensed matter physics and spintronics. So far, several theoretical and experimental proposals have been made to realize LHE, but all are based on antiferromagnetic systems. Here, using symmetry and tight-binding model analysis, we propose a general mechanism for engineering layertronics in a two-dimensional ferromagnetic multiferroic lattice. The physics is related to the band geometric properties and multiferroicity, which results in the coupling between Berry curvature and layer degree of freedom, thereby generating the LHE. Using first-principles calculations, we further demonstrate this mechanism in bilayer (BL) TcIrGe2S6. Due to the intrinsic inversion and time-reversal symmetry breakings, BL TcIrGe2S6 exhibits multiferroicity with large Berry curvatures at both the center and corners of the Brillouin zone. These Berry curvatures couple with the layer physics, forming the LHE in BL TcIrGe2S6. Our work opens a new direction for research on layertronics.

Stacking-induced phonon transport engineering of siligene

Tunable phonon transport properties of two-dimensional materials are desirable for effective heat management in various application scenarios. Here, we demonstrate by first-principles calculations and Boltzmann transport theory that the lattice thermal conductivity of siligene could be efficiently engineered by forming various stacking configurations. Unlike few-layer graphene, the stacked siligenes are found to be covalently bonded along the out-of-plane direction, which leads to unique dependence of the thermal conductivity on both the stacking order and layer number. Due to the restricted flexural phonon scattering induced by the horizontal reflection symmetry, the AA stacking configuration of bilayer siligene exhibits obviously higher thermal conductivity compared with the AB stacking. In addition, we observe increasing thermal conductivity with the layer number, as evidenced by the reduced phonon scattering phase space and Grüneisen parameter. Interestingly, the Fuchs-Sondheimer model works well for the thickness-dependent thermal conductivity of stacked siligenes.

Layer-Polarized Anomalous Hall Effects from Inversion-Symmetric Single-Layer Lattices

In the field of physics and materials science, the discovery of the layer-polarized anomalous Hall effect (LP-AHE) stands as a crucial development. The current research paradigm is rooted in topological or inversion-asymmetric valleytronic systems, making such a phenomenon rather rare. In this work, a universal design principle for achieving the LP-AHE from inversion-symmetric single-layer lattices is proposed. Through tight-binding model analysis, we demonstrate that by stacking into antiferromagnetic van der Waals bilayer lattices, the coupling physics between PT symmetry and vertical external bias can be realized. This coupling reveals the previously neutralized layer-locked Berry curvature, compelling the carriers to move in a specific direction within a given layer, thereby realizing the LP-AHE. Intriguingly, the chirality of the LP-AHE can be effectively switched by modulating the direction of vertical external bias. First-principles calculations validate this mechanism in bilayer T-FeCl2 and MnPSe3. Our results pave the way for new explorations of the LP-AHE.

Hidden Valley Polarization, Piezoelectricity, and Dzyaloshinskii-Moriya Interactions of Janus Vanadium Dichalcogenides

Due to the lack of inversion symmetry and the discovery of room-temperature ferromagnetism, two-dimensional semiconducting vanadium-based van der Waals transition-metal dichalcogenides (V-TMDs) are drawing attention for their possible application in spintronics and valleytronics. Here, we show the functional properties enriched by the broken inversion, out-of-plane mirror, and time-reversal symmetries of Janus H-VXY TMDs (X, Y = S, Se, Te). By first-principles calculations, we reveal the intrinsic xy easy-plane magnetism of the Janus vanadium-based TMD monolayers and systematically study their hidden valley polarization and giant magneto band structure. Their strong nearest-neighbor exchange strengths lead to near-room-temperature magnetic phase transitions. The Janus H-VXY system also exhibits piezoelectricity with nonzero e31 and e21. Interestingly, it is found that the right-handed Dzyaloshinskii-Moriya interaction has nonzero in-plane components in our Janus system, with fluctuating magnitudes determined by competence between relaxed bond-angle and atomic index of ligands.

Optimization Strategy in Hydrogen Storage Performance of Ti─V─Cr─Mn Alloys via LiAlH4

V-based solid solution materials hold a significant position in the realm of hydrogen storage materials because of its high hydrogen storage capacity. However, the current dehydrogenation temperature of V-based solid solution exceeds 350 °C, making it challenging to fulfill the appliance under moderate conditions. Here advancements in the hydrogen storage properties and related mechanisms of TiV1.1 Cr0.3 Mn0.6  + x LiAlH4 (x = 0, 5, 8, 10 wt.%) composites is presented. According to the first principle calculation analysis, the inclusion of Al and Li atoms will lower the binding energy of hydride, thus enhancing the hydrogen absorption reaction and significantly decreasing the activation difficulty. Furthermore, based on crystal orbital Hamilton population (COHP) analysis, the strength of the V─H and Ti─H bonds after doping LiAlH4 are reduced, leading to a decrease of the hydrogen release activation energy (Ea ) for the V-based solid solution material, thus the hydrogen release process is easier to carry out. Additionally, the structure of doped LiAlH4 exhibits an outstanding hydrogen release rate of 2.001 wt.% at 323 K and remarkable cycling stability.

High Spin Magnetic Moments in All-3d-Metallic Co-Based Full Heusler Compounds

We conduct ab-initio electronic structure calculations to explore a novel category of magnetic Heusler compounds, comprising solely 3d transition metal atoms and characterized by high spin magnetic moments. Specifically, we focus on Co2YZ Heusler compounds, where Y and Z represent transition metal atoms such that the order of the valence is Co > Y > Z. We show that these compounds exhibit a distinctive region of very low density of minority-spin states at the Fermi level when crystallizing in the L21 lattice structure. The existence of this pseudogap leads most of the studied compounds to a Slater-Pauling-type behavior of their total spin magnetic moment. Co2FeMn is the compound that presents the largest total spin magnetic moment in the unit cell reaching a very large value of 9 μB. Our findings suggest that these compounds are exceptionally promising materials for applications in the realms of spintronics and magnetoelectronics.

Photocatalytic water splitting properties of GeC/InS van der Waals heterostructure: First-principles calculations

Based on first-principles, we conducted an in-depth study of the GeC/InS van der Waals heterostructure formed by GeC and InS and discussed its structure, electronic properties and optical properties. First, we observe that this heterostructure has negative binding energy, indicating that the interlayer interactions are mainly affected by van der Waals forces. Through band structure and density of state analysis, we confirmed its type-II band alignment characteristics, which means that photogenerated carriers have the ability to automatically separate in space. Moreover, the average charge density difference and Bader charge analysis show that there is a built-in electric field in the heterostructure, and further proves that GeC/InS forms a Z-scheme charge transfer mechanism. Interestingly, the band edge position spans the water redox potential and can fully induce the redox reaction of water splitting, indicating that it is a potential photocatalyst. The high light absorption coefficient shown in the absorption spectrum also further confirms its excellent photocatalytic activity. The most striking thing is that the solar hydrogen production efficiency of GeC/InS heterostructure is as high as 44.39%. Our research demonstrates the theoretical basis for GeC/InS heterostructure as a photocatalyst.

Ideal Vacuum-Based Efficient and High-Throughput Computational Screening of Type II Heterojunctions

Heterojunctions featuring a type II band alignment play a crucial role in a wide range of devices, particularly in the realm of solar cells. However, the design of such heterojunctions with a specific type of band alignment poses a substantial challenge due to the immense number of potential combinations of bulk semiconductors and their relative orientations. In this study, we propose an efficient, high-throughput computational screening method tailored for heterojunctions. Our approach, using the ideal vacuum level as a reference energy, eliminates the need for explicit electronic structure calculations for junctions. Through this protocol, we identify 1041 type II heterojunctions out of 2692 structures constructed from 86 selected inorganic compounds with appropriate band gaps sourced from the Inorganic Crystal Structure Database. For potential application in solar cells, we assess these heterojunctions, and remarkably, 58 of them exhibit a power conversion efficiency (PCE) exceeding 15%, with 13 surpassing the 20% threshold. Test calculations with expensive interface models confirm the reliability of PCE predictions based on ideal vacuums. These predictions will be of benefit in assessing the material applicability for solar cell applications. Furthermore, the versatility of our proposed screening method extends beyond solar cells, making it a valuable theoretical design tool that can be applied to a wide range of heterojunction devices.

Valley filters using graphene blister defects from first principles

Valleytronics, which makes use of the two valleys in graphenes, attracts considerable attention and a valley filter is expected to be the central component in valleytronics. We propose the application of the graphene valley filter using blister defects to the investigation of the valley-dependent transport properties of the Stone-Wales and blister defects of graphenes by density functional theory calculations. It is found that the intervalley transition from theKvalley to theK'valleys is completely suppressed in some defects. Using a large bipartite honeycomb cell (BHC) including several carbon atoms in a cell and replacing atomic orbitals with molecular orbitals in the tight-binding model, we demonstrate analytically and numerically that the symmetry between the A and B sites of the BHC contributes to the suppression of the intervalley transition. In addition, the universal rule for the atomic structures of the blisters suppressing the intervalley transition is derived. Furthermore, by introducing additional carbon atoms to graphenes to form blister defects, we can split the energies of the states at which resonant scattering occurs on theKandK'channel electrons. Because of this split, the fully valley-polarized current will be achieved by the local application of a gate voltage.

Electronic and magnetic properties of layered M3Si2Te6(M = alkaline earth and transition metals)

Recently, a new layered material, Mn3Si2Te6, was identified to be a semiconductor with nodal-line topological property and ferrimagnetic ground state. In this work, we propose a series of structures, M3Si2Te6(M = alkaline earth and transition metals), and systematically investigate their mechanical, magnetic and electronic properties, and the strain effect to enrich the family of the layered materials for practical applications. We find 13 stable M3Si2Te6, including 5 semiconductors (M = Ca, Sr, Fe, Ru and Os) and 8 metals (M = Sc, Ti, Nb, Ta, Cr, Mo, W and Tc). Two structures (M = Ti and Cr) are antiferromagnetic (AFM), while other structures are non-magnetic (NM). Similar to Mn3Si2Te6, the AFM structures exhibit magnetic anisotropy energies (MAEs) and semiconductors have anisotropic electron effective masses. We further show that compressions along thez-axis can effectively tune the electronic and magnetic properties, such as the semiconductor-metal and NM-AFM transition in Fe3Si2Te6, the two-fold degeneracy of the valence band maximums in Sr3Si2Te6, as well as the reduced MAE for all magnetic structures. These results demonstrate the diverse properties of the layered M3Si2Te6family and provide promising theoretical predictions for the future design of new layered materials.

First-principles investigation of the electronics, optical, mechanical, thermodynamics and thermoelectric properties of Na based Quaternary Heusler alloys (QHAs) NaHfXGe (X = Co, Rh, Ir)

In this study, we explored the electronic and thermoelectric (TE) properties of the Na-based Quaternary Heusler Alloys (QHAs) NaHfXGe (X = Co, Rh, Ir) using density functional theory (DFT). We performed the spin-polarized DFT calculations at the general gradient approximation (GGA) level and confirmed the ground state non-magnetic configuration of NaHfXGe. The mechanical and thermodynamical stabilities are analyzed and discussed to validate the stability by calculating the elastic constant and phonon dispersion curve. A thorough investigation on the electronic properties are carried out by performing the GGA, GGA+U, and GGA+SOC formalism where we report the semi-conducting characteristic of NaHfCoGe and NaHfRhGe QHAs. However, NaHfIrGe is predicted to be a non-magnetic metal. From the calculated optical properties we found that the most active optical absorption occurs within the vis-UV region withα>105 cm-1, therefore the studied QHAs are proposed to be a promising optoelectronic materials. The results of the thermodynamic properties have shown that NaHfXGe follows Debye's low-temperature specific heat law and the classical thermodynamics of the Dulong-Petit law at high temperatures. The calculated TE efficiency using GGA+SOC formalism atT= 1200 K are ZT∼1.22 and 0.57 for NaHfCoGe and NaHfRhGe, suggesting that these materials are potential TE materials to operate at high temperature.

Electric Field-Controlled Magneto-Optical Kerr Effect in A-Type Antiferromagnetic Fe2CX2 (X = F, Cl) and Its Janus Monolayer

The magneto-optical Kerr effect (MOKE) is a powerful probe of magnetism and has recently gained new attention in antiferromagnetic (AFM) materials. Through extensive first-principles calculations and group theory analysis, we have identified Fe2CX2 (X = F, Cl) and Janus Fe2CFCl monolayers as ideal A-type collinear AFM materials with high magnetic anisotropy and Néel temperatures. By applying a vertical external electrical field (Ef) of 0.2 V/Å, the MOKE is activated for Fe2CF2 and Fe2CCl2 monolayers without changing their magnetic ground state, and the maximum Kerr rotation angles are 0.13 and 0.08°, respectively. Due to the out-of-plane spontaneous polarization, the intrinsic and nonvolatile MOKE is found in the Janus Fe2CFCl monolayer and the maximal Kerr rotation angle without external electronic field is 0.25°. Moreover, the intrinsic built-in electronic field also gives origin to more robust A-type AFM ordering and reversible Kerr angle against external Ef. Our study suggests that Ef is an effective tool for controlling MOKE in two-dimensional (2D) AFM materials. This research opens the possibility of related studies and applications in AFM spintronics.

Superconductivity Above 100 K Predicted in Carbon-Cage Network

To explore carbide superconductors with higher transition temperature, two novel carbon structures of cage-network are designed and their superconductivity is studied by doping metals. MC6 and MC10 are respectively identified as C24 and C32 cage-network structures. This study finds that both carbon structures drive strong electron-phonon interaction and can exhibit superconductivity above liquid nitrogen temperature. Importantly, the superconducting transition temperatures above 100 K are predicted to be achieved in C24 -cage-network systems doped by Na, Mg, Al, In, and Tl at ambient pressure, which is far higher than those in graphite, fullerene, and other carbides. Meanwhile, the superconductivity of cage-network carbides is also found to be sensitive to the electronegativity and concentration of dopant M. The result indicates that the higher transition temperatures can be obtained by optimizing the carbon-cage-network structures and the doping conditions. The study suggests that the carbon-cage-network structure is a direction to explore high-temperature superconducting carbides.

Surface functionalization of graphene-like boron arsenide monolayer: a first-principles study

In this work, the effects of hydrogen (H) and oxygen (O) adsorption on the electronic and magnetic properties of graphene-like boron arsenide (BAs) monolayer are investigated using first-principles calculations. Pristine monolayer is a non-magnetic two-dimensional (2D) material, exhibiting direct gap semiconductor character with band gap of 0.75 (1.18) eV as calculated by generalized gradient approximation with Perdew-Burke-Ernzerhof (HSE06) functional. Four high-symmetry adsorption sites are considered, including on-top of B atom (TB), on-top of As atom (TAs), on-top of hollow site (TH), and on-top of bridge site (Tbridge). Using the criterion of adsorption energy, it is found thatTBandTbridgesites are favorable adsorption sites for H and O adatom, respectively. The analysis of electronic interactions indicate the charge transfer from host BAs monolayer to both adatoms. H adsorption conducts to the emergence of magnetic semiconductor nature in BAs monolayer with a total magnetic moment of 1.00 μB. Herein, the magnetism is originated mainly from H adatom and its neighbor As atoms. In contrast, the non-magnetic nature of BAs monolayer is preserved upon absorbing O atoms. In this case, the energy gap exhibits a slight reduction of 4%. Further, the effects of adatom coverage are also analyzed. The presented results suggest an effective modification of ground state electronic properties, as well as induction of new feature-rich properties to make new multifunctional 2D materials from non-magnetic BAs monolayer.

Role of Native Defects in Fe-Doped β-Ga2O3

Iron impurities are believed to act as deep acceptors that can compensate for the n-type conductivity in as-grown Ga2O3, but several scientific issues, such as the site occupation of the Fe heteroatom and the complexes of Fe-doped β-Ga2O3 with native defects, are still lacking. In this paper, based on first-principle density functional theory calculations with the generalized gradient approximation approach, the controversy regarding the preferential Fe incorporation on the Ga site in the β-Ga2O3 crystal has been addressed, and our result demonstrates that Fe dopant is energetically favored on the octahedrally coordinated Ga site. The structural stabilities are confirmed by the formation energy calculations, the phonon dispersion relationships, and the strain-dependent analyses. The thermodynamic transition level Fe3+/Fe2+ is located at 0.52 eV below the conduction band minimum, which is consistent with Ingebrigtsen's theoretical conclusion, but slightly smaller than some experimental values between 0.78 eV and 1.2 eV. In order to provide direct guidance for material synthesis and property design in Fe-doped β-Ga2O3, the defect formation energies, charge transitional levels, and optical properties of the defective complexes with different kinds of native defects are investigated. Our results show that VGa and Oi can be easily formed for the Fe-doped β-Ga2O3 crystals under O-rich conditions, where the +3 charge state FeGaGai and -2 charge state FeGaOi are energetically favorable when the Fermi level approaches the valence and conduction band edges, respectively. Optical absorption shows that the complexes of FeGaGai and FeGaVGa can significantly enhance the optical absorption in the visible-infrared region, while the energy-loss function in the β-Ga2O3 material is almost negligible after the extra introduction of various intrinsic defects.

Electronic, Thermal and Mechanical Properties of Carbon and Boron Nitride Holey Graphyne Monolayers

In a recent experimental accomplishment, a two-dimensional holey graphyne semiconducting nanosheet with unusual annulative π-extension has been fabricated. Motivated by the aforementioned advance, herein we theoretically explore the electronic, dynamical stability, thermal and mechanical properties of carbon (C) and boron nitride (BN) holey graphyne (HGY) monolayers. Density functional theory (DFT) results reveal that while the C-HGY monolayer shows an appealing direct gap of 1.00 (0.50) eV according to the HSE06(PBE) functional, the BNHGY monolayer is an indirect insulator with large band gaps of 5.58 (4.20) eV. Furthermore, the elastic modulus (ultimate tensile strength) values of the single-layer C- and BN-HGY are predicted to be 127(41) and 105(29) GPa, respectively. The phononic and thermal properties are further investigated using machine learning interatomic potentials (MLIPs). The predicted phonon spectra confirm the dynamical stability of these novel nanoporous lattices. The room temperature lattice thermal conductivity of the considered monolayers is estimated to be very close, around 14.0 ± 1.5 W/mK. At room temperature, the C-HGY and BN-HGY monolayers are predicted to yield an ultrahigh negative thermal expansion coefficient, by more than one order of magnitude larger than that of the graphene. The presented results reveal decent stability, anomalously low elastic modulus to tensile strength ratio, ultrahigh negative thermal expansion coefficients and moderate lattice thermal conductivity of the semiconducting C-HGY and insulating BN-HGY monolayers.

Anisotropy and isotope effect in superconducting solid hydrogen

Elucidating the phase diagram of solid hydrogen is a key objective in condensed matter physics. Several decades ago, it was proposed that at low temperatures and high pressures, solid hydrogen would be a metal with a high superconducting transition temperature. This transition to a metallic state can happen through the closing of the energy gap in the molecular solid or through a transition to an atomic solid. Recent experiments have managed to reach pressures in the range of 400-500 GPa, providing valuable insights. There is strong evidence suggesting that metallization via either of these mechanisms occurs within this pressure range. Computational and experimental studies have identified multiple promising crystal phases, but the limited accuracy of calculations and the limited capabilities of experiments prevent us from determining unequivocally the observed phase or phases. Therefore, it is crucial to investigate the superconducting properties of all the candidate phases. Recently, we reported the superconducting properties of theC2/c-24,Cmca-12,Cmca-4 andI41/amd-2 phases, including anharmonic effects. Here, we report the effects of anisotropy on superconducting properties using Eliashberg theory. Then, we investigate the superconducting properties of deuterium and estimate the size of the isotope effect for each phase. We find that the isotope effect on superconductivity is diminished by anharmonicity in theC2/c-24 andCmca-12 phases and enlarged in theCmca-4 andI41/amd-2 phases. Our anharmonic calculations of theC2/c-24 phase of deuterium agree closely with the most recent experiment by Loubeyreet al(2022Phys. Rev. Lett.29035501), indicating that theC2/c-24 phase remains the leading candidate in this pressure range, and has a strong anharmonic character. These characteristics can serve to distinguish among crystal phases in experiment. Furthermore, expanding our understanding of superconductivity in pure hydrogen holds significance in the study of high-Tchydrides.

Fluorination and Conjugation Engineering Synergistically Enhance the Optoelectronic Properties of Two-Dimensional Hybrid Organic-Inorganic Perovskites

Two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs) are expected to be a viable alternative to three-dimensional (3D) analogs in solar cells (SCs) and optoelectronic devices due to their high stability, diverse composition, and physical properties. However, unsuitable band alignment and large bandgaps limit the power conversion efficiency (PCE) improvement of SCs based on 2D HOIPs. Here, we report a molecular design strategy that combines fluorination and conjugation engineering to tune the electronic structure and optimize the PCE of 2D HOIPs. Our results show that type IIa band alignment and tunable bandgaps can be achieved in 2D Dion-Jacobson (DJ) HOIPs by H/F substitution of organic cations with different degrees of conjugation. In general, the bandgap of 2D DJ-HOIPs decreases monotonously with the increase of the number of F atoms, which is due to the gradual decrease of the lowest unoccupied molecular orbitals (LUMO) of organic cations. In addition, the enhanced interlayer charge transfer and higher dielectric constant suggest that the fluorination-induced dielectric limitations are weakened. The estimated PCE of 2D DJ-HOIPs is exponentially increased and positively correlated with the degree of conjugation and fluorination of organic cations, with a PCE approaching 29% under their synergistic effect. Our results not only provide promising candidates for photovoltaic device applications but also provide an effective method for PCE optimization.

Electrolyte Coatings for High Adhesion Interfaces in Solid-State Batteries from First Principles

We introduce an adhesion parameter that enables rapid screening for materials interfaces with high adhesion. This parameter is obtained by density functional theory calculations of individual single-material slabs rather than slabs consisting of combinations of two materials, eliminating the need to calculate all configurations of a prohibitively vast space of possible interface configurations. Cleavage energy calculations are used as an upper bound for electrolyte and coating energies and implemented in an adapted contact angle equation to derive the adhesion parameter. In addition to good adhesion, we impose further constraints in electrochemical stability window, abundance, bulk reactivity, and stability to screen for coating materials for next-generation solid-state batteries. Good adhesion is critical in combating delamination and resistance to lithium diffusivity in solid-state batteries. Here, we identify several promising coating candidates for the Li7La3Zr2O12 and sulfide electrolyte systems including the previously investigated electrode coating materials LiAlSiO4 and Li5AlO8, making them especially attractive for experimental optimization and commercialization.

Hybrid deep modeling of a CHO-K1 fed-batch process: combining first-principles with deep neural networks

Introduction: Hybrid modeling combining First-Principles with machine learning is becoming a pivotal methodology for Biopharma 4.0 enactment. Chinese Hamster Ovary (CHO) cells, being the workhorse for industrial glycoproteins production, have been the object of several hybrid modeling studies. Most previous studies pursued a shallow hybrid modeling approach based on three-layered Feedforward Neural Networks (FFNNs) combined with macroscopic material balance equations. Only recently, the hybrid modeling field is incorporating deep learning into its framework with significant gains in descriptive and predictive power. Methods: This study compares, for the first time, deep and shallow hybrid modeling in a CHO process development context. Data of 24 fed-batch cultivations of a CHO-K1 cell line expressing a target glycoprotein, comprising 30 measured state variables over time, were used to compare both methodologies. Hybrid models with varying FFNN depths (3-5 layers) were systematically compared using two training methodologies. The classical training is based on the Levenberg-Marquardt algorithm, indirect sensitivity equations and cross-validation. The deep learning is based on the Adaptive Moment Estimation Method (ADAM), stochastic regularization and semidirect sensitivity equations. Results and conclusion: The results point to a systematic generalization improvement of deep hybrid models over shallow hybrid models. Overall, the training and testing errors decreased by 14.0% and 23.6% respectively when applying the deep methodology. The Central Processing Unit (CPU) time for training the deep hybrid model increased by 31.6% mainly due to the higher FFNN complexity. The final deep hybrid model is shown to predict the dynamics of the 30 state variables within the error bounds in every test experiment. Notably, the deep hybrid model could predict the metabolic shifts in key metabolites (e.g., lactate, ammonium, glutamine and glutamate) in the test experiments. We expect deep hybrid modeling to accelerate the deployment of high-fidelity digital twins in the biopharma sector in the near future.

First-Principles Study on Si Atom Diffusion Behavior in Ni-Based Superalloys

The Si atom diffusion behavior in Ni-based superalloys was evaluated based on first-principles calculations. Also, the site occupation of Si atoms as the melting point depressant elements in Cr, Mo, and W atom doped γ-Ni and γ'-Ni3Fe supercells was discussed and Si atom diffusion behaviors between both adjacent octahedral interstices were analyzed. Calculation results indicated that formation enthalpy (∆Hf) was decreased, stability was improved by doping alloying elements Cr, Mo, and W in γ-Ni and γ'-Ni3Fe supercells, Si atoms were more inclined to occupy octahedral interstices and the diffusion energy barrier was increased by increasing the radius of the doped alloy element. Especially, two diffusion paths were available for Si atoms in the γ'-Ni3Fe and Si diffusion energy barrier around the shared Fe atoms between adjacent octahedral interstices and was significantly lower than that around the shared Ni atoms. The increase of interaction strength between the doped M atom/octahedron constituent atom and Si atom increased Si atom diffusion and decreased the diffusion energy barrier. The Si atom diffusion behavior provides a theoretical basis for the phase structure evolution in wide-gap brazed joints.

First-Principles Investigation of Size Effects on Cohesive Energies of Transition-Metal Nanoclusters

The cohesive energy of transition-metal nanoparticles is crucial to understanding their stability and fundamental properties, which are essential for developing new technologies and applications in fields such as catalysis, electronics, energy storage, and biomedical engineering. In this study, we systematically investigate the size-dependent cohesive energies of all the 3d, 4d, and 5d transition-metal nanoclusters (small nanoparticles) based on a plane-wave-based method within general gradient approximation using first-principles density functional theory calculations. Our results show that the cohesive energies of nanoclusters decrease with decreasing size due to the increased surface-to-volume ratio and quantum confinement effects. A comparison of nanoclusters with different geometries reveals that the cohesive energy decreases as the number of nanocluster layers decreases. Notably, monolayer nanoclusters exhibit the lowest cohesive energies. We also find that the size-dependent cohesive energy trends are different for different transition metals, with some metals exhibiting stronger size effects than others. Our findings provide insights into the fundamental properties of transition-metal nanoclusters and have potential implications for their applications in various fields, such as catalysis, electronics, and biomedical engineering.

Aluminene as a Low-Cost Anode Material for Li- and Na-Ion Batteries

Two-dimensional (2D) materials are promising candidates for next-generation battery technologies owing to their high surface area, excellent electrical conductivity, and lower diffusion energy barriers. In this work, we use first-principles density functional theory to explore the potential for using a 2D honeycomb lattice of aluminum, referred to as aluminene, as an anode material for metal-ion batteries. The metallic monolayer shows strong adsorption for a range of metal atoms, i.e., Li, Na, K, and Ca. We observe surface diffusion barriers as low as 0.03 eV, which correlate with the size of the adatom. The relatively low average open-circuit voltages of 0.27 V for Li and 0.42 V for Na are beneficial to the overall voltage of the cell. The estimated theoretical specific capacity has been found to be 994 mA h/g for Li and 870 mA h/g for Na. Our research highlights the promise of aluminene sheets in the development of low-cost, high-capacity, and lightweight advanced rechargeable ion batteries.

First-principles predictions of enhanced thermoelectric properties for Cs2SnI2Cl2and Cs2PbI2Cl2monolayers with spin-orbit coupling

Inspired by the exceptional charge transport properties and ultra-low thermal conductivity of halide perovskite, we investigate the electronic nature, thermal transport, and thermoelectric properties for Ruddlesden-Popper all-inorganic perovskite, Cs2SnI2Cl2and Cs2PbI2Cl2monolayers, using first-principles calculations. During the calculations, spin-orbit coupling has been considered for electronic transport as well as thermoelectric properties. The results show that the Cs2SnI2Cl2and Cs2PbI2Cl2monolayers exhibit high carrier mobility and low thermal conductivity. Stronger phonon-phonon interaction is responsible for the fact that thermal conductivity of Cs2SnI2Cl2monolayer is much lower than that of Cs2PbI2Cl2monolayer. At 700 K, the values of the figure of merit (ZT) for the n-type doped Cs2SnI2Cl2and Cs2PbI2Cl2monolayers are about 1.05 and 0.32 at the optimized carrier concentrations 5.42 × 1012cm-2and 9.84 × 1012cm-2. Moreover, when spin-orbit coupling is considered, the correspondingZTvalues are enhanced to 2.73 and 1.98 at 5.27 × 1011cm-2and 6.16 × 1011cm-2. These results signify that Cs2SnI2Cl2and Cs2PbI2Cl2monolayers are promising thermoelectric candidates.

Effects of Cu, Zn Doping on the Structural, Electronic, and Optical Properties of α-Ga2O3: First-Principles Calculations

The intrinsic n-type conduction in Gallium oxides (Ga2O3) seriously hinders its potential optoelectronic applications. Pursuing p-type conductivity is of longstanding research interest for Ga2O3, where the Cu- and Zn-dopants serve as promising candidates in monoclinic β-Ga2O3. However, the theoretical band structure calculations of Cu- and Zn-doped in the allotrope α-Ga2O3 phase are rare, which is of focus in the present study based on first-principles density functional theory calculations with the Perdew-Burke-Ernzerhof functional under the generalized gradient approximation. Our results unfold the predominant Cu1+ and Zn2+ oxidation states as well as the type and locations of impurity bands that promote the p-type conductivity therein. Furthermore, the optical calculations of absorption coefficients demonstrate that foreign Cu and Zn dopants induce the migration of ultraviolet light to the visible-infrared region, which can be associated with the induced impurity 3d orbitals of Cu- and Zn-doped α-Ga2O3 near the Fermi level observed from electronic structure. Our work may provide theoretical guidance for designing p-type conductivity and innovative α-Ga2O3-based optoelectronic devices.

First-principles design of g-C3N4/HfSSe heterojunctions for optoelectronic applications

Based on first-principles calculations, the structure, electronic and optical properties of g-C3N4/HfSSe heterojunctions have been systematically explored. We prove the stability of two heterojunctions by comparing the binding energies from six different stacking heterojunctions, which name are g-C3N4/SHfSe heterojunction and g-C3N4/SeHfS heterojunction, respectively. It is shown that both heterojunctions behave direct band gaps with type II band alignment. The charge is rearranged at the interface after the heterojunctions are formed, which results in the formation of the built-in electric field. In the ultraviolet, visible and near-infrared regions, excellent light absorption is found in g-C3N4/HfSSe heterojunctions.

Layer Hall Effect in Multiferroic Two-Dimensional Materials

The layer Hall effect (LHE) is of fundamental and practical importance in condensed-matter physics and material science; however, it was rarely observed and usually based on the paradigms of persistent electric field and sliding ferroelectricity. Here, a new mechanism of LHE is proposed by coupling layer physics with multiferroics using symmetry analysis and a low-energy k·p model. Due to time-reversal symmetry breaking and valley physics, the Bloch electrons on one valley will be subject to a large Berry curvature. This combined with inversion symmetry breaking gives rise to layer-polarized Berry curvature and can force the electrons to deflect in one direction of a given layer, thereby generating the LHE. We demonstrate that the resulting LHE is ferroelectrically controllable and reversible. Using first-principles calculations, this mechanism and predicted phenomena are verified in the multiferroic material of bilayer Co₂CF₂. Our finding opens a new direction for LHE and 2D materials research.

Bandgap Engineering of Two-Dimensional Double Perovskite Cs4AgBiBr8/WSe2 Heterostructure from Indirect Bandgap to Direct Bandgap by Introducing Se Vacancy

Heterostructures based on layered materials are considered next-generation photocatalysts due to their unique mechanical, physical, and chemical properties. In this work, we conducted a systematic first-principles study on the structure, stability, and electronic properties of a 2D monolayer WSe₂/Cs₄AgBiBr₈ heterostructure. We found that the heterostructure is not only a type-II heterostructure with a high optical absorption coefficient, but also shows better optoelectronic properties, changing from an indirect bandgap semiconductor (about 1.70 eV) to a direct bandgap semiconductor (about 1.23 eV) by introducing an appropriate Se vacancy. Moreover, we investigated the stability of the heterostructure with Se atomic vacancy in different positions and found that the heterostructure was more stable when the Se vacancy is near the vertical direction of the upper Br atoms from the 2D double perovskite layer. The insightful understanding of WSe₂/Cs₄AgBiBr₈ heterostructure and the defect engineering will offer useful strategies to design superior layered photodetectors.

Tunable electronic and optical properties of MoTe2/InSe heterostructure via external electric field and strain engineering

Based on first-principles calculation under density functional theory, the geometry, electronic and optical properties of the MoTe₂/InSe heterojunction have been investigated. The results reveal that the MoTe₂/InSe heterojunction has a typical type-Ⅱ band alignment and exhibits an indirect bandgap of 0.99 eV. In addition, the Z-scheme electron transport mechanism is capable of efficiently separating photogenerated carriers. The bandgap of the heterostructure changes regularly under applied electric field and exhibits a significant Giant Stark effect. Under an applied electric field of 0.5 V Å^-1, the band alignment of the heterojunction shifts from type-Ⅱ to type-I. The application of strain produced comparable changes in the heterojunction. More importantly, the transition from semiconductor to metal is completed in the heterostructure under the applied electric field and strain. Furthermore, the MoTe₂/InSe heterojunction retains the optical properties of two monolayers and produces greater light absorption on this basis, especially for UV light. The above results offer a theoretical basis for the application of MoTe₂/InSe heterostructure in the next generation of photodetectors.

Substrate Strain Engineering of Single-Atomic Sn-N4 Sites Embedded in Various Carbon Matrixes for Bifunctional Oxygen Electrocatalysis

It is still a great challenge to design and synthesize high-efficiency and low-cost single-atom catalysts (SACs) as promising bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Herein, theoretical insights into Sn-N₄ embedded carbon nanotubes, graphene quantum dots, and graphene nanosheets (denoted as Sn-N₄-CNTs, Sn-N₄-GQDs, and Sn-N₄-Gra, respectively) for the ORR/OER are systematically provided. These results show that the protruding Sn atom creates a Sn-N₄ pyramid and induces varied strain transfer between Sn-N₄ and different carbon substrates prior to adsorption of O intermediates, resulting in the opposite response of the adsorption strengths of O intermediates to the substrate curvature of Sn-N₄-CNTs and Sn-N₄-GQDs. The torsional strain induced by OH* and OOH* on the Sn atom of Sn-N₄-CNTs breaks the scaling relations between the adsorption strengths of O intermediates. Consequently, Sn-N₄-CNTs with suitable curvature achieve outstanding ORR performance with very low overpotentials (0.28 V). Furthermore, the increase of curvature boosts the OER activity of Sn-N₄-CNTs. For Sn-N₄-GQDs, high curvature contributes to promoted OER activity but reduced ORR activity. The electronic interactions reveal the electron transfer from the s/p-bands of Sn to the half-filled β states of the frontier orbitals of O intermediates.

Friction properties of black phosphorus: a first-principles study

Based on the first-principle, the friction anisotropy, structural super-lubricity and oxidation induced ultra-low friction of black phosphorus at atomic scale under different loads have been studied. The results show that the interface friction of black phosphorus is anisotropic, that is, the friction along the armchair direction is greater than that along the zigzag direction. Moreover, the friction between the black phosphorus interfaces shows a structural superlubricity property, and the incommensurate interface friction is approximately one thousandth of the commensurate interface friction, which is mainly due to the less electronic charge and the smaller amplitude of electronic charge change between the incommensurate interfaces during the friction process. In addition, the oxidation of black phosphorus is beneficial for lubrication between interfaces.

The Effect of Hydrogen on Plastic Anisotropy of Mg and α-Ti/Zr from First-Principles Calculations

Mg and α-Ti/Zr exhibit high plastic anisotropy. In this study, the ideal shear strength across the basal, prismatic, pyramidal I, and pyramidal II slip systems in Mg and α-Ti/Zr with and without hydrogen was computed. The findings indicate that hydrogen reduces the ideal shear strength of Mg across the basal and pyramidal II slip systems, as well as of α-Ti/Zr across all four systems. Moreover, the activation anisotropy of these slip systems was analyzed based on the dimensionless ideal shear strength. The results suggest that hydrogen increases the activation anisotropy of these slip systems in Mg, while decreasing it in α-Ti/Zr. Furthermore, the activation possibility of these slip systems in polycrystalline Mg and α-Ti/Zr subjected to uniaxial tension was analyzed by utilizing the ideal shear strength and Schmidt's law. The results reveal that hydrogen increases the plastic anisotropy of Mg/α-Zr alloy while decreasing that of α-Ti alloy.

Two-Dimensional Iron Silicide (FeSix) Alloys with Above-Room-Temperature Ferromagnetism

Two-dimensional (2D) materials with intrinsic room-temperature ferromagnetism have gathered tremendous interest as promising candidates for next-generation spintronics. Here, on the basis of first-principles calculations, we report a family of stable 2D iron silicide (FeSi_x) alloys via dimensional reduction of their bulk counterparts. Our results demonstrate that 2D Fe₄Si₂-hex, Fe₄Si₂-orth, Fe₃Si₂, and FeSi₂ nanosheets are lattice-dynamically and thermally stable, confirmed by the calculated phonon spectra and Born-Oppenheimer dynamic simulation up to 1000 K. 2D FeSi_x nanosheets are ferromagnetic metals with estimated Curie temperatures ranging from 547 to 971 K due to strong direct exchange interaction between Fe sites. In addition, the electronic properties of 2D FeSi_x alloys can be maintained on silicon substrates, providing an ideal platform for spintronics applications in the nanoscale.

Insight into the Electronic Properties of Semiconductor Heterostructure Based on Machine Learning and First-Principles

A first-principles approach is a powerful means of gaining insight into the intrinsic structure and properties of materials. However, with the implementation of material genetic engineering, it is still a challenging road to discover materials with high satisfaction. One alternative is to employ machine-learning techniques to mine data and predict performance. In this present contribution, the method is taken to predict the band gap opening value of graphene in a heterostructure. First, the data of 2076 binary compounds in the Materials Project library are used to achieve visual dimensionality reduction of the data set through a t-distributed stochastic neighbor embedding (t-SNE) algorithm in unsupervised learning. Then, a series of semiconductor components are screened out and form heterostructures with graphene. Second, by means of the ensemble learning EXtreme Gradient Boost (XGBoost) algorithm and support vector machine (SVM) technology, two prediction frameworks are built to predict the band gap opening value of the graphene in the system. Finally, density functional theory (DFT) is used to calculate the energy band and density of states for comparison. Analysis shows that the prediction model has an accuracy rate of 88.3%, and there is little difference between prediction results and calculation results. We anticipate that this framework model would have fascinating applications in predicting the electronic properties of various multiphase materials.

How a Ferroelectric Layer Can Tune a Two-Dimensional Electron Gas at the Interface of LaInO3 and BaSnO3: A First-Principles Study

The emerging interest in two-dimensional electron gases (2DEGs), formed at interfaces between two insulating oxide perovskites, poses a crucial fundamental question in view of future electronic devices. In the framework of density-functional theory, we investigate the possibility to control the characteristics of the 2DEG formed at the LaInO₃/BaSnO₃ interface by including a ferroelectric layer. To do so, we consider BaTiO₃ as a prototype example and examine how the orientation of the ferroelectric polarization impacts density and confinement of the 2DEG. We find that aligning the ferroelectric polarization toward (outward) the LaInO₃/BaSnO₃ interface leads to an accumulation (depletion) of the interfacial 2DEG. Varying its magnitude, we find a linear effect on the 2DEG charge density that is confined within the BaSnO₃ side. Analysis of the optimized geometries reveals that inclusion of the ferroelectric layer makes structural distortions at the LaInO₃/BaSnO₃ junction less pronounced, which, in turn, enhances the 2DEG density. Thicker ferroelectric layers allow for reaching higher polarization magnitude. We discuss the mechanisms behind all these findings and rationalize how the characteristics of both 2DEGs and 2D hole gases can be controlled in the considered heterostructures. Overall, our results can be generalized to other combinations of ferroelectric, polar, and nonpolar materials.

"Z"-Type Tilted Quasi-One-Dimensional Assembly of Actinide-Embedded Coinage Metal Near-Plane Superatoms and Their Optical Properties

In this work, a novel discovery that the coinage-metal near-plane superatoms (CM-NPSs) formed by embedding actinide elements into the coinage metal rings can realize the "Z"-type tilted quasi-one-dimensional (1D) direct assembly is reported. This success can be attributed to the strong bonding between the overlapping parts of adjacent superatomic motifs. First-principles calculations reveal that the motifs maintain their geometric and electronic structures robustly during the assembly process. With the accumulation of motifs, the intensity of the absorption peak increases continuously in the ultraviolet-visible (UV-Vis) absorption spectra range of 300-450 nm, resulting in the hyperchromic effect, which is closely related to the degree of the participation of Th atoms. Furthermore, the absorption spectra show a continuously tunable feature in the 450-900 nm range, as the interlayer stacking pattern leads to a pronounced redshift. More importantly, the valence 5f-shells of Th atoms have an increased contribution to the final orbitals of electronic transition, which demonstrates the advantages of the active high angular momentum electrons of actinide elements in spectral properties. These findings provide a valuable reference for the direct artificial assembly of near-plane superatoms and optical properties of superatomic assemblies embedded with rare elements.

Sugar Molecules Detection via C2N Transistor-Based Sensor: First Principles Modeling

Real-time detection of sugar molecules is critical for preventing and monitoring diabetes and for food quality evaluation. In this article, a field effect transistor (FET) based on two-dimensional nitrogenated holey graphene (C₂N) was designed, developed, and tested to identify the sugar molecules including xylose, fructose, and glucose. Both density functional theory and non-equilibrium Green's function (DFT + NEGF) were used to study the designed device. Several electronic characteristics were studied, including work function, density of states, electrical current, and transmission spectrum. The proposed sensor is made of a pair of gold electrodes joint through a channel of C₂N and a gate was placed underneath the channel. The C₂N monolayer distinctive characteristics are promising for glucose sensors to detect blood sugar and for sugar molecules sensors to evaluate food quality. The electronic transport characteristics of the sensor resulted in a unique signature for each of the sugar molecules. This proposed work suggests that the developed C₂N transistor-based sensor could detect sugar molecules with high accuracy.

Research on Interface Bonding Properties of TiAlSiN/WC-Co Doped with Graphene

Based on the first-principles method, TiAlSiN/WC-Co interface models with graphene doped into the matrix, coating, and the coating/matrix are constructed. The interface adhesion work is calculated and modeled to study the interface bonding properties from the atomic microscopic point of view. The results show that the interface bonding properties of TiAlSiN/WC-Co can be improved when the matrix is doped with the main surface of intrinsic graphene, and the interface bonding property of TiAlSiNN/WC-Co can be improved when the coating and coating/matrix are doped separately with the main surface of intrinsic graphene or single vacancy defective graphene. Furthermore, the model electronic structures are analyzed. The results show that there exist strong Si/Co and N/Co covalent bonds in the interfaces when the matrix is doped with the main surface of intrinsic graphene, which causes the adhesion work of TiAlSiN/WC/msGR/Co to be greater than that of TiAlSiN/WC-Co. Additionally, when the graphene is doped into the coating, in the interface of TiAlSiN/msGR/TiAlSiNN/WC-Co, there exist strong N/Co covalent bonds that increase the interface adhesion work. Additionally, more charge transfer and orbital hybridization exist in the coating/matrix interface doped with the main surface of intrinsic graphene or single vacancy defective graphene, which explains the essential mechanism that the adhesion work of TiAlSiNN/msGR/WC-Co is greater than that of TiAlSiNN/WC-Co, and the adhesion work of TiAlSiNN/svGR/WC-Co is greater than that of TiAlSiNN/WC-Co.

Material Selection Analysis of New Partial Discharge Sensor Electrode Plate Based on First-Principles Study

Graphene is well known for its electrical properties and can be used for sensor improvement. The first-principles study is one of the powerful tools to analyze and predict the performance of advanced materials. In this paper, microscopic material selection is performed for partial discharge sensor electrode plate materials based on first-principles study. By introducing graphene, six different microscopic electrode plate models are built based on the traditional metal electrode plates. Electrical properties including electronic structure, charge density and charge distribution of electrode plates are analyzed from the microscopic perspective when the actual partial discharge electric field is 1 V/m. Additionally, electrical transport properties of electrode plates are determined by electrical transport calculation. The results show that the double-layer graphene copper-clad electrode plate has better electrical transport capacity and higher gain characteristics when used in partial discharge sensors. This study fills the gap in the microscopic electric transport response mechanism of electrode plates, which can provide theoretical support for the improved design of partial discharge sensors.

Local Corrosion Behaviors in the Coarse-Grained Heat-Affected Zone in a Newly Developed Zr-Ti-Al-RE Deoxidized High-Strength Low-Alloy Steel

Oxide metallurgy technology can improve the microstructure of a coarse-grained heat-affected zone (CGHAZ) but introduces extra inclusions. Local corrosion behavior of the CGHAZ of a Zr-Ti-Al-RE deoxidized steel was investigated in this work using theoretical calculations and experimental verification. The modified inclusions have a (Zr-Mg-Al-Ca-RE)O_x core claded by a CaS and TiN shell. CaS dissolves first, followed by the oxide core, leaving TiN parts. This confirms that the addition of rare earth can reduce lattice distortion and prevent a galvanic couple between the inclusions and the matrix, while the chemical dissolution of CaS causes localized acidification, resulting in the pitting corrosion initiation.

Size Effect of Electrical and Optical Properties in Cr2+:ZnSe Nanowires

Previous studies have shown that the nano-crystallization process has an appreciable impact on the luminescence properties of nanocrystals, which determines their defect state composition, size and morphology. This project aims to explore the influence of nanocrystal size on the electrical and optical properties of Cr²⁺:ZnSe nanowires. A first-principles study of Cr²⁺:ZnSe nanowires with different sizes was carried out at 0 K in the density functional framework. The Cr²⁺ ion was found to prefer to reside at the surface of ZnSe nanowires. As the size of the nanocrystals decreased, a considerable short-wave-length shift in the absorption of the vis-near infrared wavelength was observed. A quantum mechanism for the wavelength tunability was discussed.

Multiple Topological Magnetism in van der Waals Heterostructure of MnTe2/ZrS2

Topological magnetism in low-dimensional systems is of fundamental and practical importance in condensed-matter physics and material science. Here, using first-principles and Monte Carlo simulations, we present that multiple topological magnetism (i.e., skyrmion and bimeron) can survive in van der Waals heterostructure MnTe₂/ZrS₂. Arising from interlayer coupling, MnTe₂/ZrS₂ can harbor a large Dzyaloshinskii-Moriya interaction. This, combined with exchange interaction, yields an intriguing skyrmion phase under a tiny magnetic field of 75 mT. Meanwhile, upon harnessing a small electric field, magnetic bimeron can be observed in MnTe₂/ZrS₂, suggesting the existence of multiple topological magnetism. Through interlayer sliding, both topological magnetisms can be switched on-off. In addition, the impacts of d_∥ and K_eff on these spin textures are revealed, and a dimensionless parameter κ is utilized to describe their joint effect. These explored phenomena and insights not only are useful for fundamental research in topological magnetism but also enable novel applications in nanodevices.

Phonon transport mechanism of HfO2ultrathin film with temperature-correction full-band Monte Carlo simulation

Hafnium dioxide (HfO₂) has been widely used in microelectronics nowadays and commonly withstands extremely high temperatures, so the investigation of its thermodynamic properties is particularly essential. This paper develops a temperature-correction full-band Monte Carlo (TFMC) method to investigate the HfO₂ultrathin film. The phonon dynamics parameters of HfO₂are calculated based on the first-principles method. TFMC can better describe the phonon cumulative distribution function in different temperatures by modifying the phonon relaxation time and heat capacity. The thermal conductivity of HfO₂ultrathin film is calculated based on the above method and is in good agreement with the literature. It is observed that the optical phonons in HfO₂ultrathin film are prominent in the phonon heat transport, which is quite different from the mechanism in common semiconductor materials. Combined with the full-band diffuse mismatch model, the Si-based HfO₂ultrathin film is studied. It is found that the existence of the interface with substrates improves the thermodynamic properties of the ultrathin film, which provides a reference for the selection of substrate materials.

Theoretical study on the electronic properties of different types of the donor:acceptor complexes

Non-fullerene organic solar cells can be classified into four forms in line with the different types of donor (D) and acceptor (A) in the active layer: all-polymer (P_D:P_A), polymer D:small-molecule A (P_D:M_A), small-molecule D:polymer A (M_D:P_A), and all-small-molecule (M_D:M_A). On the basis of having studied the electronic properties of a large number of related monomer molecules and D:A complexes, this work constructed four groups of D:A molecular pairs as described above as examples to investigate their electronic properties with first-principles density functional theory. The results show that the absolute value of the average binding energy of the P_D:P_Acomplex D18:P(NDI2HD-T) is larger than others, indicating the structure is relatively more stable. In accordance of the Bader charge analysis, the intra-molecular charge transfer of small-molecule is greater than polymers. For these blends, the intermolecular charge transfer of the all-polymer pair D18:P(NDI2HD-T) is larger, revealing that the P_D:P_Apair may result in a stronger intermolecular dipole electric field, which is beneficial to facilitate the separation of excitons. In addition, the M_D:M_Apair DRTB-T:FDICTF-2Cl and the P_D:M_Acomplex D18:FDICTF-2Cl all exhibit a larger amount of intra-molecular charge transfer, which indicates that the small-molecule acceptors in D:A complexes are conducive to promoting intra-molecular charge transfer.

Effect of strain on the electronic and optical properties of (non-)metal adsorbed NbS2monolayer

This paper investigated the performance changes brought about by the adsorption of metal and non-metal atoms on monolayer NbS₂. First-principles found that the adsorption of non-metallic atoms on the monolayer NbS₂significantly changed the surface structure, with non-metallic atoms other than F intercalated into the upper S atoms. Among them, the F atom adsorption modification system changed the metallic properties of NbS₂and tended to transform into a semiconductor. Fe and Co atoms effectively change the real part of the dielectric constant, transforming NbS₂into a metamaterial. The adsorption of noble metal atoms can improve the activity of the material. Furthermore, F(Fe, Co) atoms can induce p(n)-type doping by adjusting strain. N adsorption expands the system's electromagnetic wave absorption range and improves the material's electrical conductivity. O and Pt adsorption significantly enhanced the polarizability and photoresponse of the material, resulting in enhanced photocatalytic activity.

Theoretical Prediction of Antiferromagnetic Skyrmion Crystal in Janus Monolayer CrSi2N2As2

An antiferromagnetic skyrmion crystal (AF-SkX), a regular array of antiferromagnetic skyrmions, is a fundamental phenomenon in the field of condensed-matter physics. So far, very few proposals have been made to realize the AF-SkX, and most have been based on three-dimensional (3D) materials. Herein, using first-principles calculations and Monte Carlo simulations, we report the identification of AF-SkX in a two-dimensional lattice of the Janus monolayer CrSi2N2As2. Arising from the broken inversion symmetry and strong spin-orbit coupling, a large Dzyaloshinskii-Moriya interaction is obtained in the Janus monolayer CrSi2N2As2. This, combined with the geometric frustration of its triangular lattice, gives rise to the skyrmion physics and long-sought AF-SkX in the presence of an external magnetic field. More intriguingly, this system presents two different antiferromagnetic skyrmion phases, and such a phenomenon is distinct from those reported in 3D systems. Furthermore, by contacting with Sc2CO2, the creation and annihilation of AF-SkX in Janus monolayer CrSi2N2As2 can be achieved through ferroelectricity. These findings greatly enrich the research on antiferromagnetic skyrmions.

Influence of Group-IVA Doping on Electronic and Optical Properties of ZnS Monolayer: A First-Principles Study

Element doping is a universal way to improve the electronic and optical properties of two-dimensional (2D) materials. Here, we investigate the influence of group-ⅣA element (C, Si, Ge, Sn, and Pb) doping on the electronic and optical properties of the ZnS monolayer with a tetragonal phase by using first-principles calculations. The results indicate that the doping atoms tend to form tetrahedral structures with neighboring S atoms. In these doped models, the formation energies are all negative, indicating that the formation processes of the doped models will release energy. The formation energy is smallest for C-doped ZnS and gradually increases with the metallicity of the doping element. The doped ZnS monolayer retains a direct band gap, with this band gap changing little in other element doping cases. Moreover, intermediate states are observed that are induced by the sp³ hybridization from the doping atoms and S atoms. Such intermediate states expand the optical absorption range into the visible spectrum. Our findings provide an in-depth understanding of the electronic and optical properties of the ZnS monolayer and the associated doping structures, which is helpful for application in optoelectronic devices.

Electronic and transport properties of semimetal ZrBeSi crystal: a first-principles study

In recent years, semimetals have aroused people's research interest. Here, we systematically study phonon and electronic transport properties of the ZrBeSi with semimetal character by using the first-principles calculations together with the Boltzmann transport theory. Calculated lattice thermal conductivities of the ZrBeSi alongaandcaxes are 31.3 W (m · K)^-1and 56.0 W (m · K)^-1at room temperature, respectively, which are larger than the most semiconductors and semimetals. By comparing with other semimetals, we find that the larger lattice thermal conductivity of ZrBeSi is due to its smaller Grüneisen parameter, which indicates the weaker phonon scattering. Main contributions to the lattice thermal conductivities alongaandcaxis come from the acoustic branches, and conversely, the contributions of optical branches are very small. In addition, we calculate the Seebeck coefficient and the electron thermal conductivity of ZrBeSi based on the relaxation time approximation. The electronic transport properties of ZrBeSi exhibit strong anisotropy in bothaandbdirections. Calculated electronic thermal conductivities of pristine ZrBeSi alongaandcaxes are 8.8 W (m · K)^-1and 9.7 W (m · K)^-1at room temperature, respectively. Furthermore, we also obtain the figure of meritZTon the basis of phonon and electron transport. The obtainedZTalongcaxis reaches a maximum of 0.11 at 900 K, demonstrating that ZrBeSi has a generalZT, but it has good heat conduction ability. Our research will help to understand the transport properties of semimetals and expand the application of semimetals to heat conduction devices. At the same time, it also provides some reference for the future experimental work.