A deep understanding of explosive sensitivities and their factors is important for safe and reliable applications.However,quantitative prediction of the sensitivities is difficult.Here,reactive molecular dynamics simu...A deep understanding of explosive sensitivities and their factors is important for safe and reliable applications.However,quantitative prediction of the sensitivities is difficult.Here,reactive molecular dynamics simulation models for high-speed piston impacts on explosive supercells were established.Simulations were also performed to investigate shock-induced reactions of various high-energy explosives.The fraction of reacted explosive molecules in an initial supercell changed linearly with the propagation distance of the shock-wave front.The corresponding slope could be used as a reaction rate for a specific shock-loading velocity.Reaction rates that varied with the shock-loading pressure exhibited two-stage linearities with different slopes.The two inflection points corresponded to the initial and accelerated reactions,which respectively correlated to the thresholds of shock-induced ignition and detonation.Therefore,the ignition and detonation critical pressures could be determined.The sensitivity could then be a quantitative prediction of the critical pressure.The accuracies of the quantitative shock sensitivity predictions were verified by comparing the impact and shock sensitivities of common explosives and the characteristics of anisotropic shock-induced reactions.Molecular dynamics simulations quantitatively predict and rank shock sensitivities by using only crystal structures of the explosives.Overall,this method will enable the design and safe use of explosives.展开更多
Low-pressure air plasma cleaning is an effective method for removing organic contaminants on large-aperture optical components in situ in the inertial confinement fusion facility.Chemical reactions play a significant ...Low-pressure air plasma cleaning is an effective method for removing organic contaminants on large-aperture optical components in situ in the inertial confinement fusion facility.Chemical reactions play a significant role in plasma cleaning,which is a complex process involving abundant bond cleavage and species generation.In this work,experiments and reactive molecular dynamics simulations were carried out to unravel the reaction mechanism between the benchmark organic contaminants of dibutyl phthalate and air plasma.The optical emission spectroscopy was used to study the overall evolution behaviors of excited molecular species and radical signals from air plasma as a reference to simulations.Detailed reaction pathways were revealed and characterized,and specific intermediate radicals and products were analyzed during experiments and simulation.The reactive species in the air plasma,such as O,HO2and O3radicals,played a crucial role in cleaving organic molecular structures.Together,our findings provide an atomic-level understanding of complex reaction processes of low-pressure air plasma cleaning mechanisms and are essential for its application in industrial plasma cleaning.展开更多
Machine learning(ML)has gained significant traction in engine-related research,particularly because of its potential to improve predictive performance while reducing computational costs.However,most current applicatio...Machine learning(ML)has gained significant traction in engine-related research,particularly because of its potential to improve predictive performance while reducing computational costs.However,most current applications rely on feedforward neural networks(FNNs;e.g.,conventional artificial neural networks(ANNs));these are well-suited for modeling static data and capturing nonlinear relationships,but do not explicitly encode temporal dependencies unless sequence context is introduced via feature engineering.Motivated by this limitation,we evaluate sequence-aware neural surrogates for engine-relevant combustion-chemistry time-series data.Specifically,the temporal evolution of an intermediate product group during polycyclic aromatic hydrocarbon(PAH)formation in C2H4/NH3 pyrolysis is modeled using reactive force field(ReaxFF)molecular dynamics(MD)trajectories,comparing an FNN baseline(with explicit time as an input)against a long short-term memory(LSTM)-based recurrent neural network(RNN).The results show that while the FNN baseline benefits from explicit temporal feature engineering,its predictive performance is inferior to that of the LSTM model,even when the network depth is increased.This behavior is consistent with the architectural limitations of feedforward models,which do not maintain an internal memory state,and therefore,tend to generalize poorly when the target dynamics are history dependent.In contrast,the LSTM model leverages gated memory to learn temporal dependencies and consequently improves the predictive accuracy of combustion-chemistry time-series modeling,providing an efficient surrogate once trained.Overall,our findings delineate the conditions under which sequence-aware recurrent architectures offer advantages over feedforward models for ReaxFF MD time-series surrogate modeling.展开更多
Numerous researchers in the energy field are engaged in a competitive race to advance hydrogen as a clean and environmentally friendly fuel.Studies have been conducted on the different aspects of hydrogen,including it...Numerous researchers in the energy field are engaged in a competitive race to advance hydrogen as a clean and environmentally friendly fuel.Studies have been conducted on the different aspects of hydrogen,including its production,storage,transportation and utilization.The catalytic methane decomposition technique for hydrogen production is an environmentally friendly process that avoids generating carbon dioxide gas,which contributes to the greenhouse effect.Catalysts play a crucial role in facilitating rapid,cost-effective and efficient production of hydrogen using this technique.In this study,reactive molecular dynamics simulations were employed to examine the impact of Pt7 cluster decoration on the surface of a Ni(110)catalyst,referred to as Pt7-Ni(110),on the rates of methane dissociation and molecular hydrogen production.The reactive force field was employed to model the atomic interactions that enabled the formation and dissociation of chemical bonds.Our reactive molecular dynamics simulations using the Pt7-Ni(110)catalyst revealed a notable decrease in the number of methane molecules,specifically~11.89 molecules per picosecond.The rate was approximately four times higher than that of the simulation system utilizing a Ni(110)catalyst and approximately six times higher than that of the pure methane,no-catalyst system.The number of hydrogen molecules generated during a simulation period of 150000 fs was greater on the Pt7-Ni(110)surface than in both the Ni(110)and pure methane systems.This was due to the presence of numerous dissociated hydrogen atoms on the Pt7-Ni(110)surface.展开更多
Cold atmospheric plasma(CAP)has emerged as a promising technology for the degradation of organic dyes,but the underlying mechanisms at the molecular level remain poorly understood.Using density-functional tight-bindin...Cold atmospheric plasma(CAP)has emerged as a promising technology for the degradation of organic dyes,but the underlying mechanisms at the molecular level remain poorly understood.Using density-functional tight-binding(DFTB)-based quantum chemical molecular dynamics at 300 K,we have performed numerical simulations to investigate the degradation mechanism of Disperse Red 1(DR)interacting with CAP-generated oxygen radicals.One hundred directdynamics trajectories were calculated for up to 100 ps simulation time,after which hydrogenabstraction,benzene ring-opening/expanding,formaldehyde formation and modification in the chromophoric azo group which can lead to color-losing were observed.The latter was obtained with yields of around 6%at the given temperature.These findings not only enhance our understanding of CAP treatment processes but also have implications for the development of optimized purification systems for sustainable wastewater treatment.This study underscores the utility of DFTB simulations in unraveling complex chemical processes and guiding the design of advanced treatment strategies in the context of CAP technology.展开更多
Batteries power numerous technolo-gies,yet higher energy density de-mands push lithium cobalt oxide(Li-CoO2referred as LCO)cathodes to higher voltages,triggering unwanted chemical reactions.In this work,we in-vesti...Batteries power numerous technolo-gies,yet higher energy density de-mands push lithium cobalt oxide(Li-CoO2referred as LCO)cathodes to higher voltages,triggering unwanted chemical reactions.In this work,we in-vestigate how carbonate-based elec-trolytes degrade on deeply delithiated LCO surfaces via extensive reactive molecular dynamics simulations.These simulations unveil the forma-tion of characteristic gas products and unstable surface species,which can undermine the cathode structure and reduce battery performance.By examining different solvent composi-tions,the simulations reveal that partial fluorination reduces oxidative degradation and gas evolution,thus offering a route to improve interface stability.Overall,this study provides an atomic-level perspective on preventing unwanted reactions and guiding the design of safer and more robust battery systems for high-voltage applications.展开更多
Chemical inclusions significantly alter shock responses of crystalline explosives in macroscale gap experiments but their microscale dynamics origin remains unclear.Herein shock-induced energy localization,overall phy...Chemical inclusions significantly alter shock responses of crystalline explosives in macroscale gap experiments but their microscale dynamics origin remains unclear.Herein shock-induced energy localization,overall physical responses,and reactions in a-1,3,5-trinitro-1,3,5-triazinane(a-RDX)crystal entrained various chemical inclusions were investigated by the multi-scale shock technique implemented in the reactive molecular dynamics method.Results indicated that energy localization and shock reaction were affected by the intrinsic factors within chemical inclusions,i.e.,phase states,chemical compositions,and concentrations.The atomic origin of chemical-inclusions effects on energy localization is dependent on the dynamics mechanism of interfacial molecules with free space volume,which includes homogeneous intermolecular compression,interfacial impact and shear,and void collapse and jet.As introducing various chemical inclusions,the initiation of those dynamics mechanisms triggers diverse decay rates of bulk RDX molecules and hereby impacts on growth speeds of final reactions.Adding chemical inclusions can reduce the effectiveness of the void during the shock impacting.Under the shockwave velocity of 9 km/s,the parent RDX decay rate in RDX entrained amorphous carbon decreases the most and is about one fourth of that in RDX with a vacuum void,and solid HMX and TATB inclusions are more reactive than amorphous carbon but less reactive than dry air or acetone inclusions.The lessdense shocking system denotes the greater increases in local temperature and stress,the faster energy liberation,and the earlier final reaction into equilibrium,revealing more pronounced responses to the present intense shockwave.The quantitative models associated with the relative system density(RDsys)were proposed for indicating energy-localization mechanisms and evaluating initiation safety in the shocked crystalline explosive.RDsysis defined by the density ratio of defective RDX to perfect crystal after dynamics relaxation and reveals the global density characteristic in shocked systems filled with chemical inclusions.When RDsysis below 0.9,local hydrodynamic jet initiated by void collapse dominates upon energy localization instead of interfacial impact.This study sheds light on novel insights for understanding the shock chemistry and physical-based atomic origin in crystalline explosives considering chemical-inclusions effects.展开更多
Biomass chemical looping gasification technology is one of the essential ways to utilize abundant biomass resources.At the same time,dimethyl carbonate can replace phosgene as an environmentfriendly organic material f...Biomass chemical looping gasification technology is one of the essential ways to utilize abundant biomass resources.At the same time,dimethyl carbonate can replace phosgene as an environmentfriendly organic material for the synthesis of polycarbonate.In this paper,a novel system coupling biomass chemical looping gasification with dimethyl carbonate synthesis with methanol as an intermediate is designed through microscopic mechanism analysis and process optimization.Firstly,reactive force field molecular dynamics simulation is performed to explore the reaction mechanism of biomass chemical looping gasification to determine the optimal gasification temperature range.Secondly,steady-state simulations of the process based on molecular dynamics simulation results are carried out to investigate the effects of temperature,steam to biomass ratio,and oxygen carrier to biomass ratio on the syngas yield and compositions.In addition,the main energy indicators of biomass chemical looping gasification process including lower heating value and cold gas efficiency are analyzed based on the above optimum parameters.Then,two synthesis stages are simulated and optimized with the following results obtained:the optimal temperature and pressure of methanol synthesis stage are 150℃ and 4 MPa;the optimal temperature and pressure of dimethyl carbonate synthesis stage are 140℃ and 0.3 MPa.Finally,the pre-separation-extraction-decantation process separates the mixture of dimethyl carbonate and methanol generated in the synthesis stage with 99.11%purity of dimethyl carbonate.Above results verify the feasibility of producing dimethyl carbonate from the perspective of multi-scale simulation and realize the multi-level utilization of biomass resources.展开更多
Lithium metal batteries(LMBs)represent a promising frontier in energy storage technology,offering high energy density but facing significant challenges.In this work,we address the critical challenge of lithium dendrit...Lithium metal batteries(LMBs)represent a promising frontier in energy storage technology,offering high energy density but facing significant challenges.In this work,we address the critical challenge of lithium dendrite for-mation in LMBs,a key barrier to their efficiency and safety.Focusing on the potential of electrolyte additives,specifically lithium nitrate,to inhibit dendritic growth,we employ advanced multi-scale simulation techniques to explore the formation and properties of the solid electrolyte interphase(SEI)on the anode surface.Our study introduces a novel hybrid simulation methodology,HAIR(Hybrid ab initio and Reactive force field Molecular Dynamics),which combines ab initio molecular dynamics(AIMD)and reactive force field molecular dynamics(RMD).This approach allows for a more precise and reliable examination of the interaction mechanisms of nitrate additives within LMBs.Our findings demonstrate that lithium nitrate contributes to the formation of a stable and fast ionic conductor interface,effectively suppressing dendrite growth.These insights not only advance our un-derstanding of dendrite formation and mitigation strategies in lithium metal batteries,but also highlight the efficacy of HAIR as a pioneering tool for simulating complex chemical interactions in battery materials,offering significant implications for the broader field of energy storage technology.展开更多
This study developed neural network potentials(NNPs)specifically tailored for pure ethylene and ethyleneammonia blended systems for the first time.The NNPs were trained on a dataset generated from density func-tional ...This study developed neural network potentials(NNPs)specifically tailored for pure ethylene and ethyleneammonia blended systems for the first time.The NNPs were trained on a dataset generated from density func-tional theory(DFT)calculations,combining the computational accuracy of DFT with a calculation speed com-parable to reactive force field methods.The NNPs are employed in reactive molecular dynamics simulations to explore the thermal decomposition reaction mechanisms of ethylene and ammonia.The simulation results revealed that adding ammonia reduces the activation energy for ethylene decomposition,thereby accelerating ethylene consumption.Furthermore,the addition of ammonia uncovers a new reaction pathway for hydrogen radical consumption,which reduces the occurrence of H-abstraction reactions from ethylene by hydrogen rad-icals.The inhibition effect of ammonia addition on soot formation mainly acts in two aspects:on the one hand,ammonia decomposition products react with carbon-containing species,ultimately producing C1-N products,thereby decreasing the carbon numbers involved in soot formation.This significantly reduces the concentrations of C5-C9molecules and key polycyclic aromatic hydrocarbons(PAHs)precursors like C2H2and C3H3.On the other hand,ammonia promotes the ring-opening reactions of six-membered carbon rings at high-temperature conditions,thereby reducing the formation of PAHs precursors.The results show that with the addition of ammonia,six-membered carbon rings tend to convert into seven-membered carbon rings at lower temperatures,while at higher temperatures,they are more likely to transform into three-and five-membered carbon rings.These variations in the transformation of six-membered carbon rings may also affect soot formation.The insights gained from understanding these fundamental chemical reaction mechanisms can guide the development of ethylene-ammonia co-firing systems.展开更多
MoS2dry film lubricants(DFLs)are widely used in space applications,but their performance can deteriorate at cold temperatures.In this study,reactive molecular dynamics simulations were used to test the hypothesis t...MoS2dry film lubricants(DFLs)are widely used in space applications,but their performance can deteriorate at cold temperatures.In this study,reactive molecular dynamics simulations were used to test the hypothesis that this deterioration is attributable to the effect of temperature on the size of MoS2wear debris generated during sliding.First,tribometer measurements of wear life confirmed the poor tribological performance of MoS2-based DFLs below room temperature.Then,simulations of the temperature-dependent fracture strength of MoS2provided a mechanism by which smaller flake-like debris may be formed by DFLs at low temperatures.Simulations of MoS2flakes of varying sizes showed that smaller flakes were more susceptible to water adsorption.However,even in the absence of water,simulations demonstrated that smaller flakes were less lubricious.Analysis of the flake orientation with respect to the shear direction revealed that smaller flakes were less aligned with shear during sliding.This misorientation along with the accelerated adsorption of water by the smaller flakes may contribute to deterioration of the tribological performance at cold temperatures.展开更多
The passivation of hydrogen atoms and the conformation of textured surfaces under oil-lubricated conditions are effective strategies to obtain amorphous carbon(a-C)films with extremely low friction.It is critical to u...The passivation of hydrogen atoms and the conformation of textured surfaces under oil-lubricated conditions are effective strategies to obtain amorphous carbon(a-C)films with extremely low friction.It is critical to understanding the influence mechanism of selective surface hydrogenation on the tribological behaviors of textured a-C film under oil-lubricated conditions.In particular,the interactions of hydrogen atoms and lubricants are confusing,which is enslaved to the in situ characterization technique.The reactive molecular dynamics(RMD)simulations were conducted to analyze the friction response of textured a-C films with selective hydrogenation surfaces under oil-lubricated conditions.The results indicate that the existence of hydrogen atoms on specific bump sites significantly decreases the friction coefficient(μ)of textured a-C film,which is highly dependent on the surface hydrogen content.The repulsion between hydrogen atoms and lubricant molecules prompts the formation of a dense lubricant film on the surface of the mating material.Interestingly,with the enhancement of the surface hydrogen content,the passivation of the friction interface and the repulsion between hydrogen atoms and lubricants play dominant roles in reducing the friction coefficient instead of hydrodynamic lubrication.展开更多
The roughness of the contact surface exerts a vital role in rubbing.It is still a significant challenge to understand the microscopic contact of the rough surface at the atomic level.Herein,the rough surface with a sp...The roughness of the contact surface exerts a vital role in rubbing.It is still a significant challenge to understand the microscopic contact of the rough surface at the atomic level.Herein,the rough surface with a special root mean square(RMS)value is constructed by multivariate Weierstrass–Mandelbrot(W–M)function and the rubbing process during that the chemical mechanical polishing(CMP)process of diamond is mimicked utilizing the reactive force field molecular dynamics(ReaxFF MD)simulation.It is found that the contact area A/A0 is positively related with the load,and the friction force F depends on the number of interfacial bridge bonds.Increasing the surface roughness will increase the friction force and friction coefficient.The model with low roughness and high lubrication has less friction force,and the presence of polishing liquid molecules can decrease the friction force and friction coefficient.The RMS value and the degree of damage show a functional relationship with the applied load and lubrication,i.e.,the RMS value decreases more under larger load and higher lubrication,and the diamond substrate occurs severer damage under larger load and lower lubrication.This work will generate fresh insight into the understanding of the microscopic contact of the rough surface at the atomic level.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.11832006).
摘要A deep understanding of explosive sensitivities and their factors is important for safe and reliable applications.However,quantitative prediction of the sensitivities is difficult.Here,reactive molecular dynamics simulation models for high-speed piston impacts on explosive supercells were established.Simulations were also performed to investigate shock-induced reactions of various high-energy explosives.The fraction of reacted explosive molecules in an initial supercell changed linearly with the propagation distance of the shock-wave front.The corresponding slope could be used as a reaction rate for a specific shock-loading velocity.Reaction rates that varied with the shock-loading pressure exhibited two-stage linearities with different slopes.The two inflection points corresponded to the initial and accelerated reactions,which respectively correlated to the thresholds of shock-induced ignition and detonation.Therefore,the ignition and detonation critical pressures could be determined.The sensitivity could then be a quantitative prediction of the critical pressure.The accuracies of the quantitative shock sensitivity predictions were verified by comparing the impact and shock sensitivities of common explosives and the characteristics of anisotropic shock-induced reactions.Molecular dynamics simulations quantitatively predict and rank shock sensitivities by using only crystal structures of the explosives.Overall,this method will enable the design and safe use of explosives.
基金the Joint Funds of National Natural Science Foundation of China and China Academy of Engineering Physics(NSAF)(No.U2030109)National Natural Science Foundation of China(No.52075129)。
摘要Low-pressure air plasma cleaning is an effective method for removing organic contaminants on large-aperture optical components in situ in the inertial confinement fusion facility.Chemical reactions play a significant role in plasma cleaning,which is a complex process involving abundant bond cleavage and species generation.In this work,experiments and reactive molecular dynamics simulations were carried out to unravel the reaction mechanism between the benchmark organic contaminants of dibutyl phthalate and air plasma.The optical emission spectroscopy was used to study the overall evolution behaviors of excited molecular species and radical signals from air plasma as a reference to simulations.Detailed reaction pathways were revealed and characterized,and specific intermediate radicals and products were analyzed during experiments and simulation.The reactive species in the air plasma,such as O,HO2and O3radicals,played a crucial role in cleaving organic molecular structures.Together,our findings provide an atomic-level understanding of complex reaction processes of low-pressure air plasma cleaning mechanisms and are essential for its application in industrial plasma cleaning.
基金supported by the National Natural Science Foundation of China(No.52306169)the Zhejiang Provincial Natural Science Foundation of China(No.LQ23E060005).
摘要Machine learning(ML)has gained significant traction in engine-related research,particularly because of its potential to improve predictive performance while reducing computational costs.However,most current applications rely on feedforward neural networks(FNNs;e.g.,conventional artificial neural networks(ANNs));these are well-suited for modeling static data and capturing nonlinear relationships,but do not explicitly encode temporal dependencies unless sequence context is introduced via feature engineering.Motivated by this limitation,we evaluate sequence-aware neural surrogates for engine-relevant combustion-chemistry time-series data.Specifically,the temporal evolution of an intermediate product group during polycyclic aromatic hydrocarbon(PAH)formation in C2H4/NH3 pyrolysis is modeled using reactive force field(ReaxFF)molecular dynamics(MD)trajectories,comparing an FNN baseline(with explicit time as an input)against a long short-term memory(LSTM)-based recurrent neural network(RNN).The results show that while the FNN baseline benefits from explicit temporal feature engineering,its predictive performance is inferior to that of the LSTM model,even when the network depth is increased.This behavior is consistent with the architectural limitations of feedforward models,which do not maintain an internal memory state,and therefore,tend to generalize poorly when the target dynamics are history dependent.In contrast,the LSTM model leverages gated memory to learn temporal dependencies and consequently improves the predictive accuracy of combustion-chemistry time-series modeling,providing an efficient surrogate once trained.Overall,our findings delineate the conditions under which sequence-aware recurrent architectures offer advantages over feedforward models for ReaxFF MD time-series surrogate modeling.
基金funded by a PFR 2023 research grant from the Ministry of Education,Culture,Research,and Technology of the Republic of Indonesia(contract number 183/E5/PG/02.00.PL/2023).
摘要Numerous researchers in the energy field are engaged in a competitive race to advance hydrogen as a clean and environmentally friendly fuel.Studies have been conducted on the different aspects of hydrogen,including its production,storage,transportation and utilization.The catalytic methane decomposition technique for hydrogen production is an environmentally friendly process that avoids generating carbon dioxide gas,which contributes to the greenhouse effect.Catalysts play a crucial role in facilitating rapid,cost-effective and efficient production of hydrogen using this technique.In this study,reactive molecular dynamics simulations were employed to examine the impact of Pt7 cluster decoration on the surface of a Ni(110)catalyst,referred to as Pt7-Ni(110),on the rates of methane dissociation and molecular hydrogen production.The reactive force field was employed to model the atomic interactions that enabled the formation and dissociation of chemical bonds.Our reactive molecular dynamics simulations using the Pt7-Ni(110)catalyst revealed a notable decrease in the number of methane molecules,specifically~11.89 molecules per picosecond.The rate was approximately four times higher than that of the simulation system utilizing a Ni(110)catalyst and approximately six times higher than that of the pure methane,no-catalyst system.The number of hydrogen molecules generated during a simulation period of 150000 fs was greater on the Pt7-Ni(110)surface than in both the Ni(110)and pure methane systems.This was due to the presence of numerous dissociated hydrogen atoms on the Pt7-Ni(110)surface.
基金the financial support from the Ministry of Higher Education,Science,and Innovations of the Republic of Uzbekistan (Nos.AL-4821012320 and AL-5921122141)。
摘要Cold atmospheric plasma(CAP)has emerged as a promising technology for the degradation of organic dyes,but the underlying mechanisms at the molecular level remain poorly understood.Using density-functional tight-binding(DFTB)-based quantum chemical molecular dynamics at 300 K,we have performed numerical simulations to investigate the degradation mechanism of Disperse Red 1(DR)interacting with CAP-generated oxygen radicals.One hundred directdynamics trajectories were calculated for up to 100 ps simulation time,after which hydrogenabstraction,benzene ring-opening/expanding,formaldehyde formation and modification in the chromophoric azo group which can lead to color-losing were observed.The latter was obtained with yields of around 6%at the given temperature.These findings not only enhance our understanding of CAP treatment processes but also have implications for the development of optimized purification systems for sustainable wastewater treatment.This study underscores the utility of DFTB simulations in unraveling complex chemical processes and guiding the design of advanced treatment strategies in the context of CAP technology.
基金support from the National Key Research and Development Program of China(No.2022YFB2502200)the Natural Science Foun-dation of Jiangsu Province(BK20230065)+2 种基金the Key Laboratory of Functional Nano&Soft Materials,the Collaborative Innovation Center of Suzhou Nano Sci-ence&Technology,the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)the 111 Project,Joint International Research Laboratory of Carbon-Based Functional Materials and Devices,Yue Liu acknowledges support from the National Natural Science Foundation of China(22303058)the Natural Science Foundation of Jiangsu Province(BK20230475).
摘要Batteries power numerous technolo-gies,yet higher energy density de-mands push lithium cobalt oxide(Li-CoO2referred as LCO)cathodes to higher voltages,triggering unwanted chemical reactions.In this work,we in-vestigate how carbonate-based elec-trolytes degrade on deeply delithiated LCO surfaces via extensive reactive molecular dynamics simulations.These simulations unveil the forma-tion of characteristic gas products and unstable surface species,which can undermine the cathode structure and reduce battery performance.By examining different solvent composi-tions,the simulations reveal that partial fluorination reduces oxidative degradation and gas evolution,thus offering a route to improve interface stability.Overall,this study provides an atomic-level perspective on preventing unwanted reactions and guiding the design of safer and more robust battery systems for high-voltage applications.
基金the financial support from National Natural Science Foundation of China(Grant Nos.11872119,12172051,and 11972329)Natural Science Foundation of Hubei Province(Grant No.2021CFB120)。
摘要Chemical inclusions significantly alter shock responses of crystalline explosives in macroscale gap experiments but their microscale dynamics origin remains unclear.Herein shock-induced energy localization,overall physical responses,and reactions in a-1,3,5-trinitro-1,3,5-triazinane(a-RDX)crystal entrained various chemical inclusions were investigated by the multi-scale shock technique implemented in the reactive molecular dynamics method.Results indicated that energy localization and shock reaction were affected by the intrinsic factors within chemical inclusions,i.e.,phase states,chemical compositions,and concentrations.The atomic origin of chemical-inclusions effects on energy localization is dependent on the dynamics mechanism of interfacial molecules with free space volume,which includes homogeneous intermolecular compression,interfacial impact and shear,and void collapse and jet.As introducing various chemical inclusions,the initiation of those dynamics mechanisms triggers diverse decay rates of bulk RDX molecules and hereby impacts on growth speeds of final reactions.Adding chemical inclusions can reduce the effectiveness of the void during the shock impacting.Under the shockwave velocity of 9 km/s,the parent RDX decay rate in RDX entrained amorphous carbon decreases the most and is about one fourth of that in RDX with a vacuum void,and solid HMX and TATB inclusions are more reactive than amorphous carbon but less reactive than dry air or acetone inclusions.The lessdense shocking system denotes the greater increases in local temperature and stress,the faster energy liberation,and the earlier final reaction into equilibrium,revealing more pronounced responses to the present intense shockwave.The quantitative models associated with the relative system density(RDsys)were proposed for indicating energy-localization mechanisms and evaluating initiation safety in the shocked crystalline explosive.RDsysis defined by the density ratio of defective RDX to perfect crystal after dynamics relaxation and reveals the global density characteristic in shocked systems filled with chemical inclusions.When RDsysis below 0.9,local hydrodynamic jet initiated by void collapse dominates upon energy localization instead of interfacial impact.This study sheds light on novel insights for understanding the shock chemistry and physical-based atomic origin in crystalline explosives considering chemical-inclusions effects.
基金supported by the National Natural Science Foundation of China(22178189)the Natural Science Foundation of Shandong Province(ZR2021MB113)the Postdoctoral Science Foundation of China(2022M711746)。
摘要Biomass chemical looping gasification technology is one of the essential ways to utilize abundant biomass resources.At the same time,dimethyl carbonate can replace phosgene as an environmentfriendly organic material for the synthesis of polycarbonate.In this paper,a novel system coupling biomass chemical looping gasification with dimethyl carbonate synthesis with methanol as an intermediate is designed through microscopic mechanism analysis and process optimization.Firstly,reactive force field molecular dynamics simulation is performed to explore the reaction mechanism of biomass chemical looping gasification to determine the optimal gasification temperature range.Secondly,steady-state simulations of the process based on molecular dynamics simulation results are carried out to investigate the effects of temperature,steam to biomass ratio,and oxygen carrier to biomass ratio on the syngas yield and compositions.In addition,the main energy indicators of biomass chemical looping gasification process including lower heating value and cold gas efficiency are analyzed based on the above optimum parameters.Then,two synthesis stages are simulated and optimized with the following results obtained:the optimal temperature and pressure of methanol synthesis stage are 150℃ and 4 MPa;the optimal temperature and pressure of dimethyl carbonate synthesis stage are 140℃ and 0.3 MPa.Finally,the pre-separation-extraction-decantation process separates the mixture of dimethyl carbonate and methanol generated in the synthesis stage with 99.11%purity of dimethyl carbonate.Above results verify the feasibility of producing dimethyl carbonate from the perspective of multi-scale simulation and realize the multi-level utilization of biomass resources.
基金support from National Key Research and Development Program of China(No.2022YFB2502200)National Natural Science Foundation of China(22173066)+5 种基金Natural Science Foundation of Jiangsu Province(BK20230065)Suzhou Key Laboratory of Functional Nano&Soft MaterialsCollaborative Innovation Center of Suzhou Nano Science&TechnologyPriority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)the 111 ProjectJoint International Research Laboratory of Carbon-Based Functional Materials and Devices.
摘要Lithium metal batteries(LMBs)represent a promising frontier in energy storage technology,offering high energy density but facing significant challenges.In this work,we address the critical challenge of lithium dendrite for-mation in LMBs,a key barrier to their efficiency and safety.Focusing on the potential of electrolyte additives,specifically lithium nitrate,to inhibit dendritic growth,we employ advanced multi-scale simulation techniques to explore the formation and properties of the solid electrolyte interphase(SEI)on the anode surface.Our study introduces a novel hybrid simulation methodology,HAIR(Hybrid ab initio and Reactive force field Molecular Dynamics),which combines ab initio molecular dynamics(AIMD)and reactive force field molecular dynamics(RMD).This approach allows for a more precise and reliable examination of the interaction mechanisms of nitrate additives within LMBs.Our findings demonstrate that lithium nitrate contributes to the formation of a stable and fast ionic conductor interface,effectively suppressing dendrite growth.These insights not only advance our un-derstanding of dendrite formation and mitigation strategies in lithium metal batteries,but also highlight the efficacy of HAIR as a pioneering tool for simulating complex chemical interactions in battery materials,offering significant implications for the broader field of energy storage technology.
基金supported by UK Physical Sciences Research Council(EPSRC)under Grant No.EP/X019551/1Supercomputing time on ARCHER is provided by the“UK Consortium on Mesoscale Engineering Sciences(UKCOMES)”under the UK EPSRC Grant No.EP/R029598/1.
摘要This study developed neural network potentials(NNPs)specifically tailored for pure ethylene and ethyleneammonia blended systems for the first time.The NNPs were trained on a dataset generated from density func-tional theory(DFT)calculations,combining the computational accuracy of DFT with a calculation speed com-parable to reactive force field methods.The NNPs are employed in reactive molecular dynamics simulations to explore the thermal decomposition reaction mechanisms of ethylene and ammonia.The simulation results revealed that adding ammonia reduces the activation energy for ethylene decomposition,thereby accelerating ethylene consumption.Furthermore,the addition of ammonia uncovers a new reaction pathway for hydrogen radical consumption,which reduces the occurrence of H-abstraction reactions from ethylene by hydrogen rad-icals.The inhibition effect of ammonia addition on soot formation mainly acts in two aspects:on the one hand,ammonia decomposition products react with carbon-containing species,ultimately producing C1-N products,thereby decreasing the carbon numbers involved in soot formation.This significantly reduces the concentrations of C5-C9molecules and key polycyclic aromatic hydrocarbons(PAHs)precursors like C2H2and C3H3.On the other hand,ammonia promotes the ring-opening reactions of six-membered carbon rings at high-temperature conditions,thereby reducing the formation of PAHs precursors.The results show that with the addition of ammonia,six-membered carbon rings tend to convert into seven-membered carbon rings at lower temperatures,while at higher temperatures,they are more likely to transform into three-and five-membered carbon rings.These variations in the transformation of six-membered carbon rings may also affect soot formation.The insights gained from understanding these fundamental chemical reaction mechanisms can guide the development of ethylene-ammonia co-firing systems.
摘要MoS2dry film lubricants(DFLs)are widely used in space applications,but their performance can deteriorate at cold temperatures.In this study,reactive molecular dynamics simulations were used to test the hypothesis that this deterioration is attributable to the effect of temperature on the size of MoS2wear debris generated during sliding.First,tribometer measurements of wear life confirmed the poor tribological performance of MoS2-based DFLs below room temperature.Then,simulations of the temperature-dependent fracture strength of MoS2provided a mechanism by which smaller flake-like debris may be formed by DFLs at low temperatures.Simulations of MoS2flakes of varying sizes showed that smaller flakes were more susceptible to water adsorption.However,even in the absence of water,simulations demonstrated that smaller flakes were less lubricious.Analysis of the flake orientation with respect to the shear direction revealed that smaller flakes were less aligned with shear during sliding.This misorientation along with the accelerated adsorption of water by the smaller flakes may contribute to deterioration of the tribological performance at cold temperatures.
基金financially supported by the National Natural Science Foundation of China(No.52175204)Basic Research Program of Xuzhou(No.KC21041)+2 种基金Material Science and Engineering Discipline Guidance Fund of China University of Mining and Technology(No.CUMTMS202211)Graduate Innovation Program of China University of Mining and Technology(No.2022WLJCRCZL281)Jiangsu Funding Program for Excellent Postdoctoral Talent(No.2022ZB522).
摘要The passivation of hydrogen atoms and the conformation of textured surfaces under oil-lubricated conditions are effective strategies to obtain amorphous carbon(a-C)films with extremely low friction.It is critical to understanding the influence mechanism of selective surface hydrogenation on the tribological behaviors of textured a-C film under oil-lubricated conditions.In particular,the interactions of hydrogen atoms and lubricants are confusing,which is enslaved to the in situ characterization technique.The reactive molecular dynamics(RMD)simulations were conducted to analyze the friction response of textured a-C films with selective hydrogenation surfaces under oil-lubricated conditions.The results indicate that the existence of hydrogen atoms on specific bump sites significantly decreases the friction coefficient(μ)of textured a-C film,which is highly dependent on the surface hydrogen content.The repulsion between hydrogen atoms and lubricant molecules prompts the formation of a dense lubricant film on the surface of the mating material.Interestingly,with the enhancement of the surface hydrogen content,the passivation of the friction interface and the repulsion between hydrogen atoms and lubricants play dominant roles in reducing the friction coefficient instead of hydrodynamic lubrication.
基金the National Key R&D Program of China(2022YFB3404304)the National Natural Science Foundation of China(No.5217052183).
摘要The roughness of the contact surface exerts a vital role in rubbing.It is still a significant challenge to understand the microscopic contact of the rough surface at the atomic level.Herein,the rough surface with a special root mean square(RMS)value is constructed by multivariate Weierstrass–Mandelbrot(W–M)function and the rubbing process during that the chemical mechanical polishing(CMP)process of diamond is mimicked utilizing the reactive force field molecular dynamics(ReaxFF MD)simulation.It is found that the contact area A/A0 is positively related with the load,and the friction force F depends on the number of interfacial bridge bonds.Increasing the surface roughness will increase the friction force and friction coefficient.The model with low roughness and high lubrication has less friction force,and the presence of polishing liquid molecules can decrease the friction force and friction coefficient.The RMS value and the degree of damage show a functional relationship with the applied load and lubrication,i.e.,the RMS value decreases more under larger load and higher lubrication,and the diamond substrate occurs severer damage under larger load and lower lubrication.This work will generate fresh insight into the understanding of the microscopic contact of the rough surface at the atomic level.