Ab initio molecular dynamics simulation reveals the influence of entropy effect on Co@BEA zeolite-catalyzed dehydrogenation of ethane

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.

Study of structural and magnetic properties of Fe(80)P-9B(11) amorphous alloy by ab initio molecular dynamic simulation

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.

Molecular Dynamics Insights into Electron-Catalyzed Dissociation Repair of Cyclobutane Pyrimidine Dimer

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).

Effect of Y element on atomic structure, glass forming ability,and magnetic properties of FeBC alloy

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.

Structural Origins for Enhanced Thermal Stability and Glass‑Forming Ability of Co–B Metallic Glasses with Y and Nb Addition

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.

Novel Soft Magnetic Co-Based Ternary Co-Er-B Bulk Metallic Glasses

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%.

Borates as a new direction in the design of oxide ion conductors

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.

Single Iron-dimer Catalysts on MoS_(2) Nanosheet for Potential Nitrogen Activation

Electrocatalytic nitrogen reduction reaction(NRR)is a promising way to produce ammonia(NH_(3))at ambient temperature and pressure.Herein,we have constructed single Fe dimer catalysts on a molybdenum disulfide monolayer for potential nitrogen activation.By employing ab initio molecular dynamics simulations,it is suggested that a dual iron-single atom site can be dynamically formed,which exhibits the similar Fe-S-Fe structure as the nitrogenase.We further identify an iron dimer with a sulfur vacancy as the active center for realistic nitrogen activation by the free energy calculations since the bridged sulfur is easy to be released in the form of H_(2)S during the reduction process.It is shown that N_(2)mainly adsorbs on the Fe_(2)dimer at the sulfur vacancies in the pattern of side-on configuration,and the nitrogen reduction reaction is proceeded by an enzymatic mechanism.Charge analyses further show that the Fe_(2)dimer mainly works as an electron reservoir while MoS_(2)substrate with one sulfur vacancy acts as an inert carrier to stabilize the Fe_(2)dimer.Overall,our work provides important insights into how N_(2)molecules were adsorbed and activated on Fe_(2)-doped MoS_(2),and provides new ideas for the transformation of actual reaction sites during electrochemical reactions.