Transformation of long-period stacking ordered structures in Mg-Gd-Y-Zn alloys upon synergistic characterization of first-principles calculation and experiment and its effects on mechanical properties

Based on experiments and first-principles calculations,the microstructures and mechanical properties of as-cast and solution treated Mg-10Gd-4Y-xZn-0.6Zr(x=0,1,2,wt.%)alloys are investigated.The transformation process of long-period stacking ordered(LPSO)structure during solidification and heat treatment and its effect on the mechanical properties of experimental alloys are discussed.Results reveal that the stacking faults and 18R LPSO phases appear in the as-cast Mg-10Gd-4Y-1Zn-0.6Zr and Mg-10Gd-4Y-2Zn-0.6Zr alloys,respectively.After solution treatment,the stacking faults and 18R LPSO phase transform into 14H LPSO phase.The Enthalpies of formation and reaction energy of 14H and 18R LPSO are calculated based on first-principles.Results show that the alloying ability of 18R is stronger than that of 14H.The reaction energies show that the 14H LPSO phase is more stable than the 18R LPSO.The elastic properties of the 14H and 18R LPSO phases are also evaluated by first-principles calculations,and the results are in good agreement with the experimental results.The precipitation of LPSO phase improves the tensile strength,yield strength and elongation of the alloy.After solution treatment,the Mg-10Gd-4Y-2Zn-0.6Zr alloy has the best mechanical properties,and its ultimate tensile strength and yield strength are 278.7 MPa and 196.4 MPa,respectively.The elongation of Mg-10Gd-4Y-2Zn-0.6Zr reaches 15.1,which is higher than that of Mg-10Gd-4Y0.6Zr alloy.The improving mechanism of elastic modulus by the LPSO phases and the influence on the alloy mechanical properties are also analyzed.

First-principles study on stability and superconductivity of ternary hydride LaYH_(x)(x=2,3,6 and 8)

Recent studies have shown that the La-and Y-hydrides can exhibit significant superconducting properties under high pressures.In this paper,we investigate the stability,electronic and superconducting properties of LaYH_(x)(x=2,3,6 and 8)under 0-200 GPa.It is found that LaYH_(2) stabilizes in the C2/m phase at ambient pressure,and transforms to the Pmmn phase at 67 GPa.LaYH_(3) stabilizes in the C2/m phase at ambient pressure,and undergoes phase transitions of C2/m→P2_(1)/m→R3m at 12 GPa and 87 GPa,respectively.LaYH_(6) stabilizes in the P4_32_12 phase at ambient pressure,and undergoes phase transitions of P4_(3)2_(1)2→P4/mmm→Cmcm at 28 GPa and 79 GPa,respectively.LaYH_(8) stabilizes in the Imma phase at 60 GPa and transforms to the P4/mmm phase at 117 GPa.Calculations of the electronic band structures show that the P4/mmm-LaYH_(8) and all phases of LaYH_(2) and LaYH_(3) exhibit metallic character.For the metallic phases,we then study their superconducting properties.The calculated superconducting transition temperatures(T_c)are 0.47 K for C2/m-LaYH_(2) at 0 GPa,0 K for C2/m-LaYH_(3) at 0 GPa,and 55.51 K for P4/mmm-LaYH_(8) at 50 GPa.

The growth ofβphase in Mg-Gd-Y-Ni alloy by experimental and first-principles study

The paper reports on the atomic investigation aboutβphase in Mg_(96)Gd_(2)Y_(1)Ni_(1) alloy by using the first-principles study and the high-angle annular dark-field scanning transmission electron microscope(HAADF-STEM)corrected by atomic Cs.By using HAADF-STEM,the rectangularβphases were observed in the underage and peak aging stages in Mg_(96)Gd_(2)Y_(1)Ni_(1) alloy.Theβphase could be precipitated from the previously precipitatedβphase,and theβphase grew in steps when it was precipitated.A special transition structure of three atomic layer thicknesses was first observed at the edge of theβphase and the structure of this interface is probably as theβ/Mg_(1) interface for the analysis of thermodynamic characterization and electronic characterization.Theβ'phase and theβ_(H) structure were precipitated only at the edge of the length directions of theβphase.Theβ'phase continues to grow into aβphase directly without the formation ofβ_(1) phase,resulting in an increase in the length of theβphase,which is discovered for the first time.

First-principles study on the diffusion behavior of Cs and I in Cr coating

Cs and I can migrate through fuel-cladding interfaces and accelerate the cladding corrosion process induced by the fuel-cladding chemical interaction.Cr coating has emerged as an important candidate for mitigating this chemical interaction.In this study,first-principles calculations were employed to investigate the diffusion behavior of Cs and I in the Cr bulk and grain boundaries to reveal the microscopic interaction mitigation mechanisms at the fuel-cladding interface.The interaction between these two fission products and the Cr coating were studied systematically,and the Cs and I temperature-dependent diffusion coefficients in Cr were obtained using Bocquet’s oversized solute-atom model and Le Claire’s nine-frequency model,respectively.The results showed that the Cs and I migration barriers were significantly lower than that of Cr,and the Cs and I diffusion coefficients were more than three orders of magnitude larger than the Cr self-diffusion coefficient within the temperature range of Generation-IV fast reactors(below 1000 K),demonstrating the strong penetration ability of Cs and I.Furthermore,Cs and I are more likely to diffuse along the grain boundary because of the generally low migration barriers,indicating that the grain boundary serves as a fast diffusion channel for Cs and I.

First-principles study of the influences of oxygen defects upon the electronic properties of Nb-doped TiO_2 by GGA + U methods

The influence of oxygen defects upon the electronic properties of Nb-doped TiO2 has been studied by using the general gradient approximation （GGA）＋U method. Four independent models （i.e., an undoped anatase cell, an anatase cell with a Nb dopant at Ti site （NbTi）, an anatase cell with a Nb-dopant and an oxygen vacancy （NbTi＋Vo）, and an anatase cell with a Nb-dopant and an interstitial oxygen （NbTi＋Oi）） were considered. The density of states, effective mass, Bader charge, charge density, and electron localization function were calcul^ited. The results show that in the NbTi＋Vo cell both eg and t2g levels of Ti 3d orbits make contributions to the electronic conductivity, and the oxygen vacancies （Vo） collaborate with Nb-dopants to favor the high electrical conductivity by inducing the Nb-dopants to release more excess charges. In NbTi＋Oi, an unoccupied impurity level appears in the band gap, which served as an acceptor level and suppressed the electronic conductivity. The results qualitatively coincide with experimental results and possibly provide insights into the preparation of TCOs with desirable conductivity.

Mechanical Properties and Electronic Structures of M(M=Ti,V,Cr,Mn and Fe)Dopedβ-Si_(3)N_(4) from First-Principle

The structures,mechanical properties and electronic structures of M metals(M=Ti,V,Cr,Mn and Fe)dopedβ-Si_(3)N_(4) were investigated by First-principles calculations within CASTEP.The calculated lattice parameters ofβ-Si_(3)N_(4) were consistent with previous date.The cohesive energy and formation enthalpy show that initialβ-Si_(3)N_(4) has the highest structural stability.The calculated elastic constant and the Voigt-Reuss-Hill approximation indicate that elastic moduli ofβ-Si_(3)N_(4) are slightly reduced by M doping.Based on Poisson’s and Pugh’s ratio,β-Si_(3)N_(4) is a ductile material and the toughness ofβ-Si_(3)N_(4) increases with M doping,and Fe doping exhibited the best toughness.The results of density of states,charge distributions and overlapping populations indicate thatβ-Si_(3)N_(4) has the strong covalent and ionic bond strength between N and Si.

First-Principles Studies of Structural Evolutions in Cathode Materials LiMO_(2)(M=Co,Mn,Ni)

We explore the structural evolutions of stoichiometric LiMO_(2)using the first-principles calculations combined with the cluster expansion method.We automatically obtain the ground state structures of the stoichiometric LiMO_(2)by just considering the cation orderings in the quasi rock-salt structures and the following structural relaxations due to both the atomic size mismatches and the Jahn–Teller distortions.We point out that,on the one hand,the cation orderings are mainly determined by the nearest,the second nearest,and the third nearest cation interactions and can be obtained from the‘phase diagram’we have built using the relative strengths of effective cluster interaction(ECI).On the other hand,the structural relaxations are dominated by the crystal field splitting(CFS)energies,i.e.,structures with larger CFS energies are more stable.By calculating the ECIs and CFS energies for various structures of LiMO_(2),we clearly show how ECI and CFS play roles in determining the structural evolution mechanism of these systems.

First-Principles Investigation of Charge Transfer Mechanism of B-Doped 3C-SiC Semiconductor Material

This study delves into the charge transfer mechanism of boron (B)-doped 3C-SiC through first-principles investigations. We explore the effects of B doping on the electronic properties of 3C-SiC, focusing on a 12.5% impurity concentration. Our comprehensive analysis encompasses structural properties, electronic band structures, and charge density distributions. The optimized lattice constant and band gap energy of 3C-SiC were found to be 4.373 Å and 1.36 eV respectively, which is in agreement with previous research (Bui, 2012;Muchiri et al., 2018). Our results show that B doping narrows the band gap, enhances electrical conductivity, and influences charge transfer interactions. The charge density analysis reveals substantial interactions between B dopants and surrounding carbon atoms. This work not only enhances our understanding of the material’s electronic properties, but also highlights the importance of charge density analysis for characterizing charge transfer mechanisms and their implications in the 3C-SiC semiconductors.

First-Principles Study on Switching Performance and Spin Filtering Efficiency of Dimethyldihydropyrene/Cyclophanediene Single-Molecule Devices with Zigzag Graphene Nanoribbon Electrodes

Moleculardeviceswith highswitchingperformance and/or the perfect spin filtering effect have always been the pursuit with the development of molecular electronics.Hereb,yusingthe 2001.0V nonequilibrium.Green's function method in combination with the density functionaltheory,the switching performance and spin filtering properties of dimethyldihydropyrene(DHP)/cyclophanediene(CPD)photoswitchable molecule connected by carbon atomic chains(CACs)to two zigzag graphene nanoribbon electrodes have been theoretically investigated.The results show that DHP is more conductive than CPD and therefore an evident switching effect is demonstrated,and the switching ratio(RON/OFF)can reach 4.5×103.It is further revealed that the RoON/OF of DHP/CPD closely depends on the length of CACs.More specifically,the RoN/OFF values of DHP/CPD with odd-numbered CACs are larger than those with even-numbered CACs.More interestingly,a high or even perfect spin filtering effect can be obtained in these investigated DHP/CPD single-molecule devices.Our study is helpful for future design of single-molecule switches and spin filters and provides a way to optimize their performance by means of varying the length of bridging CACs.

First-Principles Calculation of the Topological Nodal-Line Semimetal FeGe_(2)

The electronic and topological properties of FeGe2 with a tetragonal crystal structure were investigated via first-principles calculations.The results demonstrate that FeGe2 in this structure exhibits anti-ferromagnetism,with two bands crossing the Fermi level nesting each other at high-symmetry points in the Brillouin zone,forming a nodal ring where the nodes intersect in momentum space.Additionally,it possesses nontrivial topological surface states.Upon inclusion of SOC(spin-orbit coupling),there are no significant changes observed in the band structure,nodal features,or surface states,indicating the persistence of its topological nodal-line characteristics.

First-Principles Study of the New Layered Ternary Metal Telluride,Eu_(2)InTe_(5)

In this study,we performed first-principles calculations using the VASP(Vienna Ab initio Simulation)software package to investigate the crystal structure,electronic structure,and optical properties of a new layered ternary metal chalcogenide,Eu_(2)InTe_(5).Our results show that Eu_(2)InTe_(5) is a non-zero-gap metal with a layered structure characterized by strong intra-layer atomic bonding and weak inter-layer interaction,which suggests its potential application as a nanomaterial.We also studied the optical properties,including the absorption coefficient,imaginary and real parts of the complex dielectric constant,and found that Eu_(2)InTe_(5) exhibits strong photoresponse characteristics at the junction of ultraviolet and visible light as well as blue-green light,with peaks at wavelengths of 389 nm and 477 nm.This suggests that it could be used in the development of UV(ultraviolet)detectors and other optoelectronic devices.Furthermore,due to its strong absorption,low loss,and low reflectivity,Eu_(2)InTe_(5) has the potential to be used as a promising photovoltaic absorption layer in solar cells.

Insight Into the Separation-of-Variable Methods for the Closed-Form Solutions of Free Vibration of Rectangular Thin Plates

The separation-of-variable(SOV)methods,such as the improved SOV method,the variational SOV method,and the extended SOV method,have been proposed by the present authors and coworkers to obtain the closed-form analytical solutions for free vibration and eigenbuckling of rectangular plates and circular cylindrical shells.By taking the free vibration of rectangular thin plates as an example,this work presents the theoretical framework of the SOV methods in an instructive way,and the bisection–based solution procedures for a group of nonlinear eigenvalue equations.Besides,the explicit equations of nodal lines of the SOV methods are presented,and the relations of nodal line patterns and frequency orders are investigated.It is concluded that the highly accurate SOV methods have the same accuracy for all frequencies,the mode shapes about repeated frequencies can also be precisely captured,and the SOV methods do not have the problem of missing roots as well.

First-Principle Study on the Electronic Structure and Optical Property of New Diluted Magnetic Semiconductor(Y_(0.75)Ca_(0.25))(Cu_(0.75)Mn_(0.25))SO

The band structure,DOSs,and optical properties of(Y_(0.75)Ca_(0.25))(Cu_(0.75)Mn_(0.25))SO,including dielectric function,absorption function,reflection function,and energy loss spectrum were studied by using the first-principles calculation.The calculation results indicate that(Y_(0.75)Ca_(0.25))(Cu_(0.75)Mn_(0.25))SO is a direct bandgap semiconductor with a bandgap of 1.1 eV.The Fermi surface is asymmetric and exhibits spin splitting phenomenon.The new type of dilute magnetic semiconductor(Y_(0.75)Ca_(0.25))(Cu_(0.75)Mn_(0.25))SO exhibits significant light loss around 70 eV,with light reflection gradually increasing after 30 eV,and light absorption mainly occurring around 8-30 eV.These results also provide a basis for the discovery of more types of 1111 phase new dilute magnetic semiconductors in the future.

First-principles calculations of electronic and magnetic properties of CeN:The LDA +U method

Electronic and magnetic properties of CeN are investigated using first-principles calculations based on density func- tional theory （DFT） with the LDA ＋ U method. Our results show that CeN is a half-metal. The majority-spin electron band structure has metallic intersections, whereas the minority-spin electron band structure has a semiconducting gap straddling the Fermi level. A small indirect energy gap occurs between X and W. The calculated magnetic moment is 0.99 μb per unit cell.

First-Principles Methods in the Investigation of the Chemical and Transport Properties of Materials under Extreme Conditions

Earth is a dynamic system. The thermodynamics conditions of Earth vary drastically depending on the depth, ranging from ambient temperature and pressure at the surface to 360 GPa and 6600 K at the core. Consequently, the physical and chemical properties of Earth’s constituents (e.g., silicate and carbonate minerals) are strongly affected by their immediate environment. In the past 30 years, there has been a tremendous amount of progress in both experimental techniques and theoretical modeling methods for material characterization under extreme conditions. These advancements have elevated our understanding of the properties of minerals, which is essential in order to achieve full comprehension of the formation of this planet and the origin of life on it. This article reviews recent computational techniques for predicting the behavior of materials under extreme conditions. This survey is limited to the application of the first-principles molecular dynamics (FPMD) method to the investigation of chemical and thermodynamic transport processes relevant to Earth Science.

Structural Modal Parameter Recognition and Related Damage Identification Methods under Environmental Excitations: A Review

Modal parameters can accurately characterize the structural dynamic properties and assess the physical state of the structure.Therefore,it is particularly significant to identify the structural modal parameters according to the monitoring data information in the structural health monitoring(SHM)system,so as to provide a scientific basis for structural damage identification and dynamic model modification.In view of this,this paper reviews methods for identifying structural modal parameters under environmental excitation and briefly describes how to identify structural damages based on the derived modal parameters.The paper primarily introduces data-driven modal parameter recognition methods(e.g.,time-domain,frequency-domain,and time-frequency-domain methods,etc.),briefly describes damage identification methods based on the variations of modal parameters(e.g.,natural frequency,modal shapes,and curvature modal shapes,etc.)and modal validation methods(e.g.,Stability Diagram and Modal Assurance Criterion,etc.).The current status of the application of artificial intelligence(AI)methods in the direction of modal parameter recognition and damage identification is further discussed.Based on the pre-vious analysis,the main development trends of structural modal parameter recognition and damage identification methods are given to provide scientific references for the optimized design and functional upgrading of SHM systems.

First-principles Study on Neutral Nitrogen Impurities in Zinc Oxide

The atomic geometries, electronic structures, and formation energies of neutral nitrogen im- purities in ZnO have been investigated by first-principles calculations. The nitrogen impuri- ties are always deep acceptors, thus having no contributions to p-type conductivity. Among all the neutral nitrogen impurities, nitrogen substituting on an oxygen site has the lowest formation energy and the shallowest acceptor level, while nitrogen .substituting on a zinc site has the second-lowest formation energy in oxygen-rich conditions. Nitrogen interstitials are unstable at the tetrahedral site and spontaneously relax into a kick-out configuration. Though nitrogen may occupy the octahedral site, the concentrations will be low for the high formation energy. The charge density distributions in various doping cases are discussed, and self-consistent results are obtained.

First-principles study of phase stability and electronic properties of RhZr

First-principles calculations were carried out to investigate the structural stabilities and electronic properties of RhZr.The plane wave based pseudopotential method was used,in which both the local density approximation（LDA） and the generalized gradient approximation（GGA） implanted in the CASTEP code were employed.The internal positions of atoms in the unit cell were optimized and the ground state properties such as lattice parameter,density of state,cohesive energies and enthalpies of formation of ortho-RhZr and cubic-RhZr were calculated.The calculation results indicate that ortho-RhZr can form more easily than cubic-RhZr and the ortho-RhZr is more stable than cubic-RhZr.The density of states（DOS） reveals that the strong bonding in the Rh-Zr and Rh-Rh or Zr-Zr interaction chains accounts for the structural stability of ortho-RhZr and the hybridization between Rh-4d states and Zr-4d states is strong.

First-principle calculations of interaction of O_2 with pyrite, marcasite and pyrrhotite surfaces

The interaction of O2 with pyrite, marcasite and pyrrhotite surfaces was studied using first-principle calculations to obtain the oxidization mechanisms of these minerals. The results show that the adsorption energy of O2 on pyrrhotite surface is the largest, followed by that on marcasite surface and then pyrite surface. O2 molecules adsorbed on pyrite, marcasite and pyrrhotite surfaces are all dissociated. The oxygen atoms and surface atoms of pyrite, marcasite and pyrrhotite surfaces have different bonding structures. Due to more atoms on pyrrhotite and marcasite surfaces interaction with oxygen atoms, the adsorption energies of O2 on pyrrhotite and marcasite surfaces are larger than that on pyrite surface. Larger values of Mulliken populations for O？Fe bond of pyrrhotite surface result in relative larger adsorption energy compared with that on marcasite surface.

First-principles study of stacking fault energies in Ni_3Al intermetallic alloys

The first-principles method based on the projector augmented wave method within the generalized gradient approximation was employed to calculate the superlattice intrinsic stacking fault（SISF） and complex stacking fault（CSF） energies of the binary Ni3Al alloys with different Al contents and the ternary Ni3Al intermetallic alloys with addition of alloying elements,such as Pd,Pt,Ti,Mo,Ta,W and Re.The results show that the energies of SISF and CSF increase significantly with increase of Al contents in Ni3Al.Addition of Pd and Pt occupying the Ni sublattices does not change the SISF and CSF energies of Ni3Al markedly in comparison with the Ni-23.75Al alloy.While addition of alloying elements,such as Ti,Mo,Ta,W and Re,occupying the Al sublattices dramatically increases the SISF and CSF energies of Ni3Al.The results suggest that the energies of SISF and CSF are dependent both on the Al contents and on the site occupancy of the ternary alloying element in Ni3Al intermetallic alloys.