微量元素对Al-Ag合金时效早期微结构演变影响的Kinetic Monte Carlo模拟研究

采用基于Multi-States Ising Model的Kinetic Monte Carlo算法,模拟研究了添加微量元素对Al-Ag合金时效初期微观结构的演变过程的影响。结果表明:在Al-Ag合金中,In,Sn,Be元素显著地抑制了合金时效初期的Ag原子偏聚,这是这些元素的原子与空位强烈地相互作用的结果。Mg元素对Ag原子的偏聚的抑制次之,添加Mg元素的合金,时效过程中出现了Mg-Ag原子团簇和Ag-Mg-Va团簇,Mg-Ag之间以及Mg-Va之间的共同作用影响了Ag原子的偏聚。Li,Cd原子与Ag原子和空位均无明显作用,因此Li和Cd元素对时效早期Ag原子的团聚影响较小。微量元素是通过与构成析出相的主要溶质元素以及空位的相互作用来实现对原子偏聚过程的影响,进而来影响Al-Ag合金的时效过程的,其中微量元素与空位的相互作用起到关键的作用。锁定单空位和空位团聚进而降低空位可动性是影响Al-Ag合金时效过程的两种重要机制。

Kinetic Monte Carlo模拟PVD薄膜生长的算法研究

提出kinetic Monte Carlo模拟物理气相沉积(physical vapor deposition,简写为PVD)薄膜生长的新算法:用红黑树搜索实现跃迁路径选择及系统跃迁概率更新,通过比较红黑树搜索、线性查找、满二元树搜索的计算效率,综合分析了这3种方法的时间复杂度和空间复杂度。结果表明红黑树搜索优于其它两种搜索方法,模拟效率最高,更适合用于执行大系统的kinetic Monte Carlo模拟。

Study on kinetics of propylene polymerizationat different temperatures via Monte Carlo simulation

The elementary reactions of propylene polymerization catalyzed by conventional Ziegler-Natta catalysts was proposed according to the comprehensive view and without considering the effect of any impurity in the material on propylene polymerization. The Monte Carlo simulation technique was employed to investigate the kinetics of propylene polymerization in order to determine the validity of the stationary state assumption and the effects of the polymerization temperature on the polymerization. The simulated total amount of active species, which only increases quickly at the beginning of the polymerization, indicates that the stationary state assumption in the studied system is valid. Moreover, significant effects of polymerization temperature on the polymerization conversion, and the molecular weight and its distribution were also analyzed. The simulated results show that the consumption rate of propylene increases with the increase of polymerization temperature; the maximum values of the number-average degree of polymerization are constant at different polymerization temperatures, however, the peak appears earlier with the higher temperature; as the polymerization temperature increases, the average molecular weight decreases and the molecular weight distribution changes greatly.

The XPK Package:A Comparison between the Extended Phenomenological Kinetic(XPK) Method and the Conventional Kinetic Monte Carlo(KMC) Method

Recently, we proposed the extended phenomenological kinetics (XPK) method, which overcomes the notorious timescale separation difficulty between fast diffusion and slow chemical reactions in conventional kinetic Monte Carlo (KMC) simulations. In the present work, we make a comprehensive comparison, based on the newly developed XPK package, between the XPK method and the conventional KMC method using a model hydrogenation reaction system. Two potential energy surfaces with different lateral interactions have been designed to illustrate the advantages of the XPK method in computational costs, parallel efficiency and the convergence behaviors to steady states. The XPK method is shown to be efficient and accurate, holding the great promise for theoretical modelling in heterogeneous catalysis, in particular, when the role of the lateral interactions among adsorbates is crucial.

Multi sites vs single site for catalytic combustion of methane over Co3O4(110):A first-principles kinetic Monte Carlo study

Single-atom catalysts have been applied in many processes recently.The difference of their kinetic behavior compared to the traditional heterogeneous catalysts has not been extensively discussed yet.Herein a complete catalytic cycle of CH4 combustion assuming to be confined at isolated single sites of the Co3O4(110)surface is computationally compared with that on multi sites.The macroscopic kinetic behaviors of CH4 combustion on Co3O4(110)is systematically and quantitatively compared between those on the single site and multi sites utilizing kinetic Monte Carlo simulations upon the energetic information from the PBE+U calculation and statistic mechanics.The key factors governing the kinetics of CH4 combustion are disclosed for both the catalytic cycles respectively following the single-site and multi-site mechanisms.It is found that cooperation of multi active sites can promote the activity of complete CH4 combustions substantially in comparison to separated single-site catalyst whereas the confinement of active sites could regulate the selectivity of CH4 oxidation.The quantitative understanding of catalytic mechanism paves the way to improve the activity and selectivity for CH4 oxidation.

Monte Carlo Simulation of Kinetics of Ammonia Oxidative Decomposition over the Commercial Propylene Ammoxidation Catalyst (Mo-Bi)

Monte Carlo method is applied to investigate the kinetics of ammonia oxidative decomposition over the commercial propylene ammoxidation catalyst(Mo-Bi). The simulation is quite in agreement with experimental results. Monte Carlo simulation proves that the process of ammonia oxidation decomposition is a two-step reaction.

Kinetic Monte Carlo Simulation of EB-PVD Film:Effects of Substrate Temperature

The 2D kinetic Monte Carlo （KMC） simulation was used to study the effects of different substrate temperatures on the microstructure of Ni-Cr films in the process of deposition by the electron beam physical vapor deposition （EB-PVD）. In the KMC model, substrate was assumed to be a ＂surface＂ of tight-packed rows, and the simulation includes two phenomena： adatom-surface collision and adatom diffusion. While the interaction between atoms was described by the embedded atom method, the jumping energy was calculated by the molecular static （MS） calculation. The initial location of the adatom was defined by the Momentum Scheme. The results reveal that there exists a critical substrate temperature which means that the lowest packing density and the highest surface roughness structure will be achieved when the temperature is lower than the smaller critical value, while the roughness of both surfaces and the void contents keep decreasing with the substrate temperature increasing until it reaches the higher critical value. The results also indicate that the critical substrate temperature rises as the deposition rate increases.

Fe-Cr二元合金微观组织演化的质量密度场耦合动力学Monte-Carlo模拟研究

本文建立了一种全新的将动力学Monte-Carlo粒子模拟与基于归一化Gauss函数基组的质量密度场空间粗粒化模型耦合的杂化模拟算法.采用该杂化模拟算法,系统对比研究了4种Cr原子含量分别为12.8%,20.0%,30.0%和40.0%的Fe-Cr合金中Cr相在温度为673 K下的时效析出动力学机制,及其时效不同阶段微观组织形貌的演变规律.研究得出Fe-Cr(12.8%)合金富Cr相时效组织形貌呈现孤立颗粒状空间分布形态,时效机制属于形核-长大(NG)机制;对于Fe-Cr(30.0%)和Fe-Cr(40.0%),富Cr相时效形貌在形核-生长及熟化阶段均呈现为三维蠕虫状空间分布特征,时效机制属于条幅分解(SD)机制;对于Fe-Cr(20.0%)合金,其富Cr相组织演化特征介于NG和SD机制之间.研究进一步发现Cr原子短程序参量可用来分析富Cr相形核-生长阶段Fe-Cr合金原子尺度结构的演变,但对于时效熟化阶段微观结构组织变化不敏感.基于空间粗粒化后Fe-Cr合金微观组织形貌,进一步分析了4种Cr原子含量下Fe-Cr合金相变动力学参数如富Cr相体积分数、平均粒径及相颗粒数密度随时效时间演变.本文建立的质量密度场耦合动力学Monte-Carlo模拟方法,为开发多尺度算法模拟合金时效动力学机制及微观组织形貌演变提供了新的思路和研究基础.

Influence of CH_3SiCl_3 Consistency on Growth Process of SiC Film by Kinetic Monte Carlo Method

CH3SiCl3 （MTS）-H2-Ar system has been applied to prepare SiC film with chemical vapor deposition （CVD） method in this paper. For three facets of SiC film, some significant influence on growth rate, surface roughness, thickness and relative density brought by MTS consistency has been mainly discussed with kinetic monte carlo （KMC） method. The simulation results show that there is a certain scale for mol ratio of H2 to MTS （H2/MTS） with different deposition temperature. When MTS consistency increases, growth rate and surface roughness of three facets all increase, which manifests approximate linearity relationship. Thickness of three facets also increases while increasing trend of three facets thickness is different obviously. Although relative density of three facets all increases, increasing trend shows a little difference with MTS consistency increasing.

Kinetic Monte Carlo simulation of microalloying effect in Al-Ag alloys

The kinetic Monte Carlo method, which based on the Multi-States Ising Model, was applied to simulate the effect of microelements on the microstructural evolution of Al-Ag alloys during initial aging stage. The simulation results suggest that the microelements In, Sn and Be have a dramatic depression effect on the Ag clustering because of their strong tendency to co-existed with vacancies. There are no significant effects on the process of Ag clustering in Al-Ag alloys containing Li or Cd, because of little interaction between Li/Cd and Ag/vacancies. Microelements can influence the aging by interacting with vacancies and the atoms of precipitated composition, in which the former seems more important. In this model, “vacancy-locking” and “vacancy clusters” are two important mechanisms in the aging process.

Kinetic Monte Carlo simulations of optimization of self-assembly quantum rings growth strategy based on substrate engineering

In this paper, the kinetic Monte Carlo simulations of the self-assembly quantum rings （QRs） based on the substrate engineering, which is related to the eventual shape of the formed quantum ring, are implemented. According to the simulation results, the availability of the QR with tunable size and the formation of smooth shape on the ideal flat substrate are checked. Through designing the substrate engineering, i.e., changing the depth, the separation and the ratio between the radius and the height of the embedded inclusions, the position and size of QR can be controlled and eventually the growth strategy of optimizing the self-assembly QRs is accomplished.

Magnetization dynamics of mixed Co–Au chains on Cu(110) substrate:Combined ab initio and kinetic Monte Carlo study

We present an investigation of the one-dimensional ferromagnetism in Au–Co nanowires deposited on the Cu（110）surface. By using the density functional theory, the influence of the nonmagnetic copper substrate Cu（110） on the magnetic properties of the bimetallic Au–Co nanowires is studied. The results show the emergence of magnetic anisotropy in the supported Au–Co nanowires. The magnetic anisotropy energy has the same order of magnitude as the exchange interaction energy between Co atoms in the wire. Our electronic structure calculation reveals the emergence of new hybridized bands between Au and Co atoms and surface Cu atoms. The Curie temperature of the Au–Co wires is calculated by means of kinetic Monte Carlo simulation. The strong size effect of the Curie temperature is demonstrated.

Kinetic Monte Carlo Simulation of Deposition of Co Thin Film on Cu(001)

A kinetic Monte Carlo （kMC） simulation is conducted to study the growth of ultrathin film of Co on Cu（001） surface. The many-body, tight-binding potential model is used in the simulation to represent the interatomic potential. The film morphology of heteroepitaxial Co film on a Cu（001） substrate at the transient and final state conditions with various incident energies is simulated. The Co covered area and the thickness of the film growth of the first two layers are investigated. The simulation results show that the incident energy influences the film growth and structure. There exists a transition energy where the interracial roughness is minimum. There are some void regions in the film in the final state, because of the influence of the island growth in the first few layers. In addition, there are deviations from ideal layer-by-layer growth at a coverage from 0 - 2 monolayers （ML）.

Influence of helium on the evolution of irradiation-induced defects in tungsten:An object kinetic Monte Carlo simulation

Understanding the evolution of irradiation-induced defects is of critical importance for the performance estimation of nuclear materials under irradiation.Hereby,we systematically investigate the influence of He on the evolution of Frenkel pairs and collision cascades in tungsten(W)via using the object kinetic Monte Carlo(OKMC)method.Our findings suggest that the presence of He has significant effect on the evolution of irradiation-induced defects.On the one hand,the presence of He can facilitate the recombination of vacancies and self-interstitial atoms(SIAs)in W.This can be attributed to the formation of immobile He-SIA complexes,which increases the annihilation probability of vacancies and SIAs.On the other hand,due to the high stability and low mobility of He-vacancy complexes,the growth of large vacancy clusters in W is kinetically suppressed by He addition.Specially,in comparison with the injection of collision cascades and He in sequential way at 1223 K,the average sizes of surviving vacancy clusters in W via simultaneous way are smaller,which is in good agreement with previous experimental observations.These results advocate that the impurity with low concentration has significant effect on the evolution of irradiation-induced defects in materials,and contributes to our understanding of W performance under irradiation.

Kinetic Monte Carlo simulation of physical vapor deposition of thin Cu film

A two-dimensional Kinetic Monte Carlo method has been developed for simulating the physical vapor deposition of thin Cu films on Cu substrate. An improved embedded atom method was used to calculate the interatomic potential and determine the diffusion barrier energy and residence time. Parameters, including incident angle,deposition rate and substrate temperature, were investigated and discussed in order to find their influences on the thin film morphology.

The Lattice Kinetic Monte Carlo Simulation of Boron Diffusion in SiGe

The lattice kinetic Monte Carlo simulation (kMCS) was applied to study the boron diffusion in Si-SiGe beyond nanotechnology. Both the interstitialcy and kick-out mechanisms of boron diffusion were considered, including the effects of annealing temperatures, boron dopant concentrations, Ge compositions, and concentrations of Si self-interstitial defects (SiI). The effects on boron diffusion caused by single and double layer(s) of SiGe phase with different Ge contents and varying boron concentrations in double layers of SiGe phase were also simulated. The results show that boron diffusion in Si and between SiGe-Si both largely increase as the temperature or concentration of SiI increases, but the boron diffusion between SiGe-Si is much less than in Si. Increasing the Ge contents in SiGe alloy could retard boron diffusion heavily, while increasing the boron concentration on SiGe phase would enhance boron diffusion.

Quantitative Simulation Study of Metal Additive Manufacturing by Kinetic Monte Carlo

Metal additive manufacturing (AM) is a disruptive manufacturing technology that takes into account the needs of complex structural forming and high-performance component forming. At present, the understanding of metal additive manufacturing simulation methods is not thorough enough, which restricts the development of metal additive manufacturing. Present work discusses the evolution of KMC method simulation results for simulating metal additive manufacturing at different length ratios and different scanning speeds. The results reveal that as the scanning speed increases, the main grains in the simulation results are transformed from coarse columnar grains to crescent-shaped grains, which are in good agreement with the existing experimental results. Besides, as the ratio of unit physical length to unit simulation length increases, the ratio of unit physical time to unit simulation time gradually decreases.

Kinetic Monte Carlo simulation of growth of BaTiO_3 thin film via pulsed laser deposition

Considering the characteristics of perovskite structure, a kinetic Monte Carlo(KMC) model, in which Born-Mayer- Huggins(BMH) potential was introduced to calculate the interatomic interactions and the bonding ratio was defined to reflect the crystallinity, was developed to simulate the growth of BaTiO3 thin film via pulsed laser deposition(PLD). Not only the atoms deposition and adatoms diffusion, but also the bonding of adatoms were considered distinguishing with the traditional algorithm. The effects of substrate temperature, laser pulse repetition rate and incident kinetic energy on BaTiO3 thin film growth were investigated at submonolayer regime. The results show that the island density decreases and the bonding ratio increases with the increase of substrate temperature from 700 to 850 K. With the laser pulse repetition rate increasing, the island density decreases while the bonding ratio increases. With the incident kinetic energy increasing, the island density decreases except 6.2 eV<Ek<9.6 eV, and the bonding ratio increases at Ek<9.6 eV. The simulation results were discussed compared with the previous experimental results.

分子尺度的复杂反应体系动力学模拟(Ⅰ) 原料分子的Monte Carlo模拟

以DCC I工艺的工业常规分析数据为基础 ,采用MonteCarlo模拟和结构导向集总相结合的方法在分子尺度上对复杂反应体系的动力学进行研究 .主要介绍了如何将原料转化为 10 0 0个分子 ,每个分子又以 19个特征表示的原料分子的MonteCarlo模拟 .结果表明生成的分子能很好地反映原料的特性 。

基于Monte Carlo模拟的化学反应动力学参数估算

提出并采用基于 Monte Carlo模拟与动力学实验相结合的化学反应动力学参数估算方法 ,由基元反应确定 Monte Carlo模拟具体做法 ,将 Monte Carlo模拟结果与动力学实验结果相比较 ,根据比较结果自动调整和优化动力学参数 ,从而无需事先确定动力学方程即可有效估算各种化学反应的动力学参数值 .采用该方法估算了丙烯氨氧化反应动力学参数 ,并对估算结果进行了分析与讨论 .