The C–H bond activation in alkane dehydrogenation reactions is a key step in determining the reaction rate.To understand the impact of entropy,we performed ab initio static and molecular dynamics free energy simulati...The C–H bond activation in alkane dehydrogenation reactions is a key step in determining the reaction rate.To understand the impact of entropy,we performed ab initio static and molecular dynamics free energy simulations of ethane dehydrogenation over Co@BEA zeolite at different temperatures.AIMD simulations showed that a sharp decrease in free energy barrier as temperature increased.Our analysis of the temperature dependence of activation free energies uncovered an unusual entropic effect accompanying the reaction.The unique spatial structures around the Co active site at different temperatures influenced both the extent of charge transfer in the transition state and the arrangement of 3d orbital energy levels.We provided explanations consistent with the principles of thermodynamics and statistical physics.The insights gained at the atomic level have offered a fresh interpretation of the intricate long-range interplay between local chemical reactions and extensive chemical environments.展开更多
The structural and magnetic properties of Fe80P9B11 amorphous alloy are investigated through ab initio molecular dynamic simulation. The structure evolution of Fe（80）P9B（11） amorphous alloy can be described in the...The structural and magnetic properties of Fe80P9B11 amorphous alloy are investigated through ab initio molecular dynamic simulation. The structure evolution of Fe（80）P9B（11） amorphous alloy can be described in the framework of topological fluctuation theory, and the fluctuation of atomic hydrostatic stress gradually decreases upon cooling. The left sub peak of the second peak of Fe–B partial pair distribution functions（PDFs） becomes pronounced below the glass transition temperature, which may be the major reason why B promotes the glass formation ability significantly. The magnetization mainly originates from Fe 3d states, while small contribution results from metalloid elements P and B. This work may be helpful for developing Fe-based metallic glasses with both high saturation flux density and glass formation ability.展开更多
Excess electrons are not only an important source of radiation damage,but also participate in the repair process of radiation damage such as cyclobutane pyrimidine dimer(CPD).Using ab initio molecular dynamics(AIMD)si...Excess electrons are not only an important source of radiation damage,but also participate in the repair process of radiation damage such as cyclobutane pyrimidine dimer(CPD).Using ab initio molecular dynamics(AIMD)simulations,we reproduce the single excess electron stepwise catalytic CPD dissociation process in detail with an emphasis on the energy levels and molecular structure details associated with excess electrons.On the basis of the AIMD simulations on the CPD aqueous solution with two vertically added excess electrons,we exclude the early-proposed[2+2]-like concerted synchronous dissociation mechanism,and analyze the difference between the symmetry of the actual reaction and the symmetry of the frontier molecular orbitals which deeply impact the mechanism.Importantly,we propose a new model of the stepwise electron-catalyzed dissociation mechanism that conforms to the reality.This work not only provides dynamics insights into the excess electron catalyzed dissociation mechanism,but also reveals different roles of two excess electrons in two bond-cleavage steps(promoting versus inhibiting).展开更多
The effects of Y and Nb addition on thermal stability,glass-forming ability(GFA),and magnetic softness of Co75B25 metallic glass(MG)were comprehensively investigated.The experimental results indicated that the thermal...The effects of Y and Nb addition on thermal stability,glass-forming ability(GFA),and magnetic softness of Co75B25 metallic glass(MG)were comprehensively investigated.The experimental results indicated that the thermal stability,GFA,and magnetic softness of the studied MGs increase in the order Co_(75)B_(25)<Co_(73)Nb_(2)B_(25)<Co_(71.5)Y_(3.5)B_(25)<Co_(69.5)Y_(3.5)Nb_(2)B_(25).The structural origins of the improved properties were revealed by ab initio molecular dynamics(AIMD)simulations and density functional theory(DFT)calculations.Results showed that the B-centered prism units are the primary structure-forming units of the four MGs,connect through vertex-,edge-,and face-shared(VS,ES,and FS)atoms,and Co-centered units tend to connect with Co/B-centered units via the intercross-shared(IS)atoms.The addition of Y and Nb not only plays the role of connecting atoms but also enhances both bond strengths and the fractions of icosahedral-like units in increasing order Co_(75)B_(25)<Co_(73)Nb_(2)B_(25)<Co_(71.5)Y_(3.5)B_(25)<Co_(69.5)Y_(3.5)Nb_(2)B_(25),which is conducive to the enhancement of the structural stability,atomic packing density,and viscosity,thereby improving thermal stability and GFA.In addition,the improvement of structural stability and homogeneity leads to enhanced magnetic softness.展开更多
The atomic structure of amorphous alloys plays a crucial role in determining both their glass-forming ability and magnetic properties. In this study, we investigate the influence of adding the Y element on the glass-f...The atomic structure of amorphous alloys plays a crucial role in determining both their glass-forming ability and magnetic properties. In this study, we investigate the influence of adding the Y element on the glass-forming ability and magnetic properties of Fe_(86-x)Y_xB_7C_7(x = 0, 5, 10 at.%) amorphous alloys via both experiments and ab initio molecular dynamics simulations. Furthermore, we explore the correlation between local atomic structures and properties. Our results demonstrate that an increased Y content in the alloys leads to a higher proportion of icosahedral clusters, which can potentially enhance both glass-forming ability and thermal stability. These findings have been experimentally validated. The analysis of the electron energy density and magnetic moment of the alloy reveals that the addition of Y leads to hybridization between Y-4d and Fe-3d orbitals, resulting in a reduction in ferromagnetic coupling between Fe atoms. This subsequently reduces the magnetic moment of Fe atoms as well as the total magnetic moment of the system, which is consistent with experimental results. The results could help understand the relationship between atomic structure and magnetic property,and providing valuable insights for enhancing the performance of metallic glasses in industrial applications.展开更多
Lithium-Selenium (Li-Se) batteries have emerged as one of the most promising candidates for next-generation energy storage systems owing to superior electronic conductivity, impressive volumetric capacity, and enhance...Lithium-Selenium (Li-Se) batteries have emerged as one of the most promising candidates for next-generation energy storage systems owing to superior electronic conductivity, impressive volumetric capacity, and enhanced compatibility with carbonate electrolyte of selenium, comparable to sulfur. Despite these advantages, the development of Li-Se batteries is impeded by several intrinsic challenges, including volume expansion during the discharge process and the consequent sluggish reaction kinetics that undermine their electrochemical performance. In this study, MIL-91(Al) is used as an electrode additive to accelerate the one-step mutual solid–solid conversion reaction between Se and Li_(2)Se in the carbonate-based electrolyte. By doing so, uncontrollable deposition of Li_(2)Se is effectively mitigated, enhancing the electrochemical performance of the system. Thus, the use of MIL-91(Al) results in reduced internal resistance and faster Li-ion transfer rate, as analyzed by SPEIS and GITT. Ab initio calculations and molecular dynamics simulations further reveal that Li_(2)Se anchors to closely situated dangling oxygens of the phosphonate group of the organic linker of MIL-91(Al), inducing relaxation of the Li-Se-Li angle and stabilizing the overall structure. Accordingly, the MIL-91(Al)-containing Li-Se cells demonstrate a high specific capacity of approximately 530 mAh g^(−1) at 1C (675 mA g^(−1)) after 100 cycles and retaining a specific capacity of 320 mAh/g even under high current rate (20C) after 200 cycles. This research underlines the importance of the use of electrocatalyst/electroadsorbent materials to enhance the redox kinetics of the conversion reactions between Se and Li_(2)Se, thus paving the way for the development of high-performance Li-Se batteries.展开更多
In this work,a series of Co-based ternary Co-Er-B bulk metallic glasses(BMGs)with excellent soft magnetic properties and high strength were developed,and the local atomic structure of a typical Co_(71.5)Er_(3.5)B_(25)...In this work,a series of Co-based ternary Co-Er-B bulk metallic glasses(BMGs)with excellent soft magnetic properties and high strength were developed,and the local atomic structure of a typical Co_(71.5)Er_(3.5)B_(25) metallic glass was studied through in situ high-energy synchrotron X-ray diffraction and ab initio molecular dynamics simulations.The results reveal that the BMG samples can be obtained in a composition region of Co_(68.5-71.5)Er_(3.5-4)B_(25-27.5) by a conventional copper-mold casting method.The Co-Er-B metallic glasses possess stronger atomic bond strengths and denser local atomic packing structure composed of a higher fraction of icosahedral-like clusters but fewer deformed body-centered cubic and crystal-like polyhedrons,and they exhibit slower atomic diffusion behaviors during solidification,as compared to Co-Y-B counterparts.The enhancement in structural stability and the retardation of atomic-ordered diffusion lead to the better glass-forming ability of the Co-Er-B alloys.The smaller magnetic anisotropy energy in the Co-Er-B metallic glasses results in a lower coercivity of less than 1.3 A/m.The Co-Er-B BMGs exhibit high-yield strength of 3560-3969 MPa along with distinct plasticity of around 0.50%.展开更多
The elucidation of the multi-scale transport phenomena of lithium ions in solid electrolyte under working conditions poses huge challenges to both experimental and theoretical realms.Highresolution ab initio molecular...The elucidation of the multi-scale transport phenomena of lithium ions in solid electrolyte under working conditions poses huge challenges to both experimental and theoretical realms.Highresolution ab initio molecular dynamics simulations are severely limited by spatial and temporal scales,hindering direct comparisons with experimental observations under room temperature and applied electric potential.Herein,classical molecular dynamics simulations under constant potential are employed to unveil the migration mechanism of Li-ions in Li_(6)PS_(5)Cl(LPSC)confined by electrode interfaces considering realistic conditions.By sophisticated manipulation of anion compositions in LPSC electrolyte,it is observed that neighboring vacancies provide effective pathways for Li-ions migration and the coordination environments evolves progressively with increasing diffusion coefficient,while the conductivity exhibits a non-monotonic peak in Li_(5.3)PS_(4.3)Cl_(1.7).The semiquantitative agreement with existing experimental resultsdemonstrates the superiority of our constant potential solid electrolytemodel,which weexpect to provide atomistic understanding towards rational design of solid electrolyte.展开更多
Lowering the operating temperature of solid oxide fuel cells(SOFCs)has extensively stimulated the development of new oxide ion conductors.Here,inspired by the structural commonalities of oxide ion conductors,the inabi...Lowering the operating temperature of solid oxide fuel cells(SOFCs)has extensively stimulated the development of new oxide ion conductors.Here,inspired by the structural commonalities of oxide ion conductors,the inability to accommodate oxygen vacancies in the rigid,isolated,3-fold tetrahedral rings of SrSi/GeO_(3)-based materials,and the considerable flexibility of BO_(n) polyhedra in terms of coordination number,rotation,deformation,and linkage,we report the first borate-base family of oxide ion conductors,(Gd/Y)_(1−x)Zn_(x)BO_(3−0.5x),through combined computational prediction and experimental verification.The oxygen vacancies in(Gd/Y)BO_(3)can be accommodated by forming B_(3)O_(8)units in isolated,3-fold,tetrahedral rings of B_(3)O_(9)and transported through a cooperative mechanism of oxygen exchange between the B_(3)O_(9)and B_(3)O_(8)units,which is assisted by the intermediate opening and extending of these units.This study opens a new scientific field of the borate system for designing and discovering oxide ion conductors.展开更多
文摘The C–H bond activation in alkane dehydrogenation reactions is a key step in determining the reaction rate.To understand the impact of entropy,we performed ab initio static and molecular dynamics free energy simulations of ethane dehydrogenation over Co@BEA zeolite at different temperatures.AIMD simulations showed that a sharp decrease in free energy barrier as temperature increased.Our analysis of the temperature dependence of activation free energies uncovered an unusual entropic effect accompanying the reaction.The unique spatial structures around the Co active site at different temperatures influenced both the extent of charge transfer in the transition state and the arrangement of 3d orbital energy levels.We provided explanations consistent with the principles of thermodynamics and statistical physics.The insights gained at the atomic level have offered a fresh interpretation of the intricate long-range interplay between local chemical reactions and extensive chemical environments.
基金supported by the National Natural Science Foundation of China(Grant No.51571115)a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘The structural and magnetic properties of Fe80P9B11 amorphous alloy are investigated through ab initio molecular dynamic simulation. The structure evolution of Fe（80）P9B（11） amorphous alloy can be described in the framework of topological fluctuation theory, and the fluctuation of atomic hydrostatic stress gradually decreases upon cooling. The left sub peak of the second peak of Fe–B partial pair distribution functions（PDFs） becomes pronounced below the glass transition temperature, which may be the major reason why B promotes the glass formation ability significantly. The magnetization mainly originates from Fe 3d states, while small contribution results from metalloid elements P and B. This work may be helpful for developing Fe-based metallic glasses with both high saturation flux density and glass formation ability.
基金supported by the National Natural Science Foundation of China(No.21873056,No.21773137,and No.21573128)。
文摘Excess electrons are not only an important source of radiation damage,but also participate in the repair process of radiation damage such as cyclobutane pyrimidine dimer(CPD).Using ab initio molecular dynamics(AIMD)simulations,we reproduce the single excess electron stepwise catalytic CPD dissociation process in detail with an emphasis on the energy levels and molecular structure details associated with excess electrons.On the basis of the AIMD simulations on the CPD aqueous solution with two vertically added excess electrons,we exclude the early-proposed[2+2]-like concerted synchronous dissociation mechanism,and analyze the difference between the symmetry of the actual reaction and the symmetry of the frontier molecular orbitals which deeply impact the mechanism.Importantly,we propose a new model of the stepwise electron-catalyzed dissociation mechanism that conforms to the reality.This work not only provides dynamics insights into the excess electron catalyzed dissociation mechanism,but also reveals different roles of two excess electrons in two bond-cleavage steps(promoting versus inhibiting).
基金This work was financially supported by the National Natural Science Foundation of China(Grant No.51871039)the Key Laboratory of Solidification Control and Digital Preparation Technology(Liaoning Province),the Supercomputing Center of Dalian University of Technology,and the Global Institute for Materials Research Tohoku Program,Tohoku University,Japan。
文摘The effects of Y and Nb addition on thermal stability,glass-forming ability(GFA),and magnetic softness of Co75B25 metallic glass(MG)were comprehensively investigated.The experimental results indicated that the thermal stability,GFA,and magnetic softness of the studied MGs increase in the order Co_(75)B_(25)<Co_(73)Nb_(2)B_(25)<Co_(71.5)Y_(3.5)B_(25)<Co_(69.5)Y_(3.5)Nb_(2)B_(25).The structural origins of the improved properties were revealed by ab initio molecular dynamics(AIMD)simulations and density functional theory(DFT)calculations.Results showed that the B-centered prism units are the primary structure-forming units of the four MGs,connect through vertex-,edge-,and face-shared(VS,ES,and FS)atoms,and Co-centered units tend to connect with Co/B-centered units via the intercross-shared(IS)atoms.The addition of Y and Nb not only plays the role of connecting atoms but also enhances both bond strengths and the fractions of icosahedral-like units in increasing order Co_(75)B_(25)<Co_(73)Nb_(2)B_(25)<Co_(71.5)Y_(3.5)B_(25)<Co_(69.5)Y_(3.5)Nb_(2)B_(25),which is conducive to the enhancement of the structural stability,atomic packing density,and viscosity,thereby improving thermal stability and GFA.In addition,the improvement of structural stability and homogeneity leads to enhanced magnetic softness.
基金Project supported by the National Key Research and Development Program of China(Grant No.2021YFB2401703)the National Natural Science Foundation of China(Grant Nos.52177005 and 51871234)the China Postdoctoral Science Foundation(Grant No.2022T150691)。
文摘The atomic structure of amorphous alloys plays a crucial role in determining both their glass-forming ability and magnetic properties. In this study, we investigate the influence of adding the Y element on the glass-forming ability and magnetic properties of Fe_(86-x)Y_xB_7C_7(x = 0, 5, 10 at.%) amorphous alloys via both experiments and ab initio molecular dynamics simulations. Furthermore, we explore the correlation between local atomic structures and properties. Our results demonstrate that an increased Y content in the alloys leads to a higher proportion of icosahedral clusters, which can potentially enhance both glass-forming ability and thermal stability. These findings have been experimentally validated. The analysis of the electron energy density and magnetic moment of the alloy reveals that the addition of Y leads to hybridization between Y-4d and Fe-3d orbitals, resulting in a reduction in ferromagnetic coupling between Fe atoms. This subsequently reduces the magnetic moment of Fe atoms as well as the total magnetic moment of the system, which is consistent with experimental results. The results could help understand the relationship between atomic structure and magnetic property,and providing valuable insights for enhancing the performance of metallic glasses in industrial applications.
文摘Lithium-Selenium (Li-Se) batteries have emerged as one of the most promising candidates for next-generation energy storage systems owing to superior electronic conductivity, impressive volumetric capacity, and enhanced compatibility with carbonate electrolyte of selenium, comparable to sulfur. Despite these advantages, the development of Li-Se batteries is impeded by several intrinsic challenges, including volume expansion during the discharge process and the consequent sluggish reaction kinetics that undermine their electrochemical performance. In this study, MIL-91(Al) is used as an electrode additive to accelerate the one-step mutual solid–solid conversion reaction between Se and Li_(2)Se in the carbonate-based electrolyte. By doing so, uncontrollable deposition of Li_(2)Se is effectively mitigated, enhancing the electrochemical performance of the system. Thus, the use of MIL-91(Al) results in reduced internal resistance and faster Li-ion transfer rate, as analyzed by SPEIS and GITT. Ab initio calculations and molecular dynamics simulations further reveal that Li_(2)Se anchors to closely situated dangling oxygens of the phosphonate group of the organic linker of MIL-91(Al), inducing relaxation of the Li-Se-Li angle and stabilizing the overall structure. Accordingly, the MIL-91(Al)-containing Li-Se cells demonstrate a high specific capacity of approximately 530 mAh g^(−1) at 1C (675 mA g^(−1)) after 100 cycles and retaining a specific capacity of 320 mAh/g even under high current rate (20C) after 200 cycles. This research underlines the importance of the use of electrocatalyst/electroadsorbent materials to enhance the redox kinetics of the conversion reactions between Se and Li_(2)Se, thus paving the way for the development of high-performance Li-Se batteries.
基金supported by the National Natural Science Foundation of China(Grant Nos.52171153 and 51871039)supported by the Department of Energy(DOE)Office of Science(DE-AC02-06CH11357)+1 种基金financial support from the Shanghai Science and Technology Committee,China(Grant No.22JC1410300)the Shanghai Key Laboratory of Material Frontiers Research in Extreme Environments(MFree),China(Grant No.22dz2260800).
文摘In this work,a series of Co-based ternary Co-Er-B bulk metallic glasses(BMGs)with excellent soft magnetic properties and high strength were developed,and the local atomic structure of a typical Co_(71.5)Er_(3.5)B_(25) metallic glass was studied through in situ high-energy synchrotron X-ray diffraction and ab initio molecular dynamics simulations.The results reveal that the BMG samples can be obtained in a composition region of Co_(68.5-71.5)Er_(3.5-4)B_(25-27.5) by a conventional copper-mold casting method.The Co-Er-B metallic glasses possess stronger atomic bond strengths and denser local atomic packing structure composed of a higher fraction of icosahedral-like clusters but fewer deformed body-centered cubic and crystal-like polyhedrons,and they exhibit slower atomic diffusion behaviors during solidification,as compared to Co-Y-B counterparts.The enhancement in structural stability and the retardation of atomic-ordered diffusion lead to the better glass-forming ability of the Co-Er-B alloys.The smaller magnetic anisotropy energy in the Co-Er-B metallic glasses results in a lower coercivity of less than 1.3 A/m.The Co-Er-B BMGs exhibit high-yield strength of 3560-3969 MPa along with distinct plasticity of around 0.50%.
基金supported by the National Key Research and Development Program of China (No. 2021YFF0500600)Natural Science Foundation of Henan Province (No. 242300421129, 252300421176 and 232301420051)National Natural Science Foundation of China (No. 22478361). The computations were performed at National Supercomputing Center in Zhengzhou, China.
文摘The elucidation of the multi-scale transport phenomena of lithium ions in solid electrolyte under working conditions poses huge challenges to both experimental and theoretical realms.Highresolution ab initio molecular dynamics simulations are severely limited by spatial and temporal scales,hindering direct comparisons with experimental observations under room temperature and applied electric potential.Herein,classical molecular dynamics simulations under constant potential are employed to unveil the migration mechanism of Li-ions in Li_(6)PS_(5)Cl(LPSC)confined by electrode interfaces considering realistic conditions.By sophisticated manipulation of anion compositions in LPSC electrolyte,it is observed that neighboring vacancies provide effective pathways for Li-ions migration and the coordination environments evolves progressively with increasing diffusion coefficient,while the conductivity exhibits a non-monotonic peak in Li_(5.3)PS_(4.3)Cl_(1.7).The semiquantitative agreement with existing experimental resultsdemonstrates the superiority of our constant potential solid electrolytemodel,which weexpect to provide atomistic understanding towards rational design of solid electrolyte.
基金the National Natural Science Foundation of China(22090043 and 21622101)Guangxi Natural Science Foundation(2019GXNSFGA245006)for financial support+2 种基金the National Natural Science Foundation of China(21527803 and 21621061)the Ministry of Science and Technology of China(2016YFA0301004)for financial supportthe funding from China Postdoctoral Science Foundation(8206300392)。
文摘Lowering the operating temperature of solid oxide fuel cells(SOFCs)has extensively stimulated the development of new oxide ion conductors.Here,inspired by the structural commonalities of oxide ion conductors,the inability to accommodate oxygen vacancies in the rigid,isolated,3-fold tetrahedral rings of SrSi/GeO_(3)-based materials,and the considerable flexibility of BO_(n) polyhedra in terms of coordination number,rotation,deformation,and linkage,we report the first borate-base family of oxide ion conductors,(Gd/Y)_(1−x)Zn_(x)BO_(3−0.5x),through combined computational prediction and experimental verification.The oxygen vacancies in(Gd/Y)BO_(3)can be accommodated by forming B_(3)O_(8)units in isolated,3-fold,tetrahedral rings of B_(3)O_(9)and transported through a cooperative mechanism of oxygen exchange between the B_(3)O_(9)and B_(3)O_(8)units,which is assisted by the intermediate opening and extending of these units.This study opens a new scientific field of the borate system for designing and discovering oxide ion conductors.
