金属Cu熔化结晶过程的分子动力学模拟

采用常温、常压分子动力学模拟技术,研究了在周期性边界条件下,由864个Cu原子构成的模型系统的熔化、结晶过程。原子间相互作用势采用EAM势。模拟结果表明：在连续升温过程中,金属Cu在1520 K熔化;以不同的冷速进行冷却,在较慢冷却条件下,液态Cu在1010 K结晶;当冷速较快时,液态Cu形成非晶态。分析了升降温过程中熔体偶分布函数、原子体积、能量、MSD随温度的变化特征。     

小尺寸金属团簇熔化过程的分子动力学模拟

运用分子动力学方法模拟了小尺寸金属团簇的熔化过程, 原子之间的作用采用嵌入原子法(EAM)模型, 计算了均方根键长涨落δ随温度的变化, 以及升温过程中团簇热容的变化. 包含55、56个原子的面心立方(FCC)结构Au团簇的熔化过程是基本相同的. 而同样结构和数目Cu团簇的熔化过程却呈现出不同的趋势. Cu55、Cu56在模拟过程中都出现了FCC结构到二十面体结构的转变. 但由于表面多出了一个原子, Cu56的热容曲线比Cu55多了一个峰, 体系出现了预熔化现象. 这表明小尺寸团簇的固液转变的过程与团簇的原子类型、几何结构和原子数目密切相关.     

高压下MgO熔化特性的分子动力学模拟

Molecular dynamics simulation was used to study the melting of MgO at high pressures. The melting temperature of MgO was accurately obtained at elevated temperature and high pressure after corrections based on the modern theory of melting. The calculated melting curve was compared with the available experimental data and other theoretical results at the pressure range of 0-135 GPa. The corrected melting temperature of MgO is in good agreement with the results from Lindemann melting equation and the twophase simulated results below 15 GPa.     

CaF2熔化温度的分子动力学模拟

The molecular dynamics method has been applied to simulate the melting temperatures of CaF 2 at elevated temperature and high pressure and to calculate the P～V equation of state of CaF 2 up to 100 GPa at 300 K. The interatomic potential was taken to be the sum of pairwise additive Coulomb, van der Waals attractions, and repulsive interactions. In addition, the shell model was used in molecular dynamics simulation. The pressure dependence of the melting temperature of CaF 2 was predicted up to 4 GPa. However, in order to account for the superheating melting of the molecular dynamic simulation, the simulated melting temperatures of CaF 2 were corrected by the modern theory of melting. Consequently, the melting temperatures of CaF 2 were accurately obtained at elevated temperature and high pressure. Therefore, it is shown that shell model molecular dynamics simulation at constant pressure indeed provides a useful tool for studying the melting temperatures of other materials under high pressures.     

中介尺度Au纳米团簇熔化的分子动力学模拟

采用分子动力学模拟技术，研究了原子个数为16～8628的 Au纳米团簇的熔化过程.采用 Johnson的EAM (embedded atom method) 模型,模拟结果表明，金属纳米团簇存在一中介尺度区域.对Au纳米团簇而言，当原子个数N >456时，团簇的热力学性质与团簇尺寸呈线性关系，熔化首先从表面开始，逐步向中心区域推进，且满足Tmb－Tmc(N)＝aN(－1/3)的关系.另外，计算了中介区域的团簇的尺寸、熔化温度、表面能、熵、焓等热力学量以及均方根位移（RMSD）等动力学量，为研究纳米团簇提供定量数据.     

金属Ni熔化前后结构变化的分子动力学模拟

使用Tight-binding势函数, 对FCC-Ni升温熔化过程的结构变化进行了分子动力学模拟. 在定压条件下模拟得到的Ni的熔点在1850 K与1900 K之间. 计算得到了体系在各温度下的径向分布函数和配位数分布等静态结构信息以及动力学性质. 计算得出的液体Ni的扩散系数在1900 K时约为5.02×10−9 m2•s−1, 与实验数据相符. 对液态体系中FCC短程有序结构可能发生的畸变以及由此导致的H-A键型变化进行了分析, 结合配位体构型搜索和键对分析方法计算了各温度下不同短程有序结构的分布. 计算表明, Ni在熔化之后仍保留有部分晶态短程结构, 但发生了较大的畸变, 同时液态中有少量的缺陷二十面体结构存在. 而液体Ni中大多数的配位体的几何构型介于FCC与缺陷二十面体之间.     

贵金属Au冷却过程中结构及能量变化的分子动力学计算机模拟

通过分子动力学方法,研究了不同冷速下贵金属Au在温度2000～300K的冷却过程中微观结构的变化特点。结果发现,冷却速度对Au的微观结构产生重要影响。采用偶关联函数和键对分析技术对原子局域团簇结构进行分析,并考察了冷却过程中原子势能随温度的变化,比较了Au的微观结构转变与能量变化的对应关系,从能量转化的角度对冷却过程中Au的结构变化进行了说明。     

金属银在高升温速率下的熔化和过热行为

采用分子动力学方法和QSC(quantum Sutton-Chen)力场研究了升温速率对金属银的熔化和过热行为的影响.模拟中考虑了缺陷和表面对熔化和过热行为的影响.研究结果表明,升温速率对金属银的熔化和过热行为有很大影响,随着升温速率的升高,金属银的熔点有所升高.高的升温速率会导致金属银体系内部无序化程度增加,降低了熔化相变的能垒.升温速率导致的银完美晶体的过热极限大约为1450 K.     

升温速率对金属铅的熔化和过热行为的影响

采用分子动力学方法和QSC(quantum Sutton-Chen)力场研究了升温速率对金属铅的熔化和过热行为的影响.模拟中考虑了缺陷和表面对熔化和过热行为的作用.结果表明，升温速率对金属铅的熔化和过热行为影响很大，随着升温速率的升高，金属铅的熔点有所升高.快的升温速率会导致金属铅体系内部无序化程度增加，进而使体系能量增加，降低了熔化相变的能垒.升温速率导致的金属铅的过热极限大约为780 K.     

液态合金NiAl凝固过程中微观结构转变的分子动力学模拟

采用分子动力学模拟方法对液态NiAl凝固过程进行了研究,考察了不同冷却速度下液态NiAl结构变化特点,原子间相互作用势采用F-S多体势,结构分析采用键取向序和对分析技术.计算结果表明,冷却速度对液态NiAl结构转变有重要影响,在不同的冷却速度下, NiAl凝固过程出现了明显不同,冷速为4×1013和4×1012 K/s时, NiAl快速凝固为无序的非晶体结构;而在较慢的8×1011 K/s冷速下, NiAl凝固为晶态结构.给出了不同冷却速度下液态NiAl结构转变的微观信息.     

Simulations of Metal Cu in Heating Process

Introduction In order to study the short-range order as well as thermodynamic properties, two distinct techniques of computer simulation, namely, the molecular dynamics and Monte Carlo methods, are most frequently em-ployed. In both techniques, the interaction potential is the primary input for computation. Mitra and co-workers1 have used a two-body model with Coulombic interac-tions and a power-law repulsion, fitted to the short- range structure and melting temperature of cristobalite. Thre…     

金属Cu低指数表面熔化行为的分子动力学模

采用Mishin镶嵌原子势, 通过分子动力学方法模拟了金属Cu的低指数表面在不同温度的表面熔化行为, 分析了熔化过程中系统结构组态的变化以及固-液界面迁移情况. 金属Cu的(100)和(110)表面在低于熔点发生预熔化, 而(111)表面存在明显的过热现象. 准液体层的厚度随温度升高而增加, 热稳定性与表面的密排顺序一致, 按(111)、(100)、(110)顺序增大. 当温度高于热力学熔点时, 固液界面的移动速度与温度成正比, 外推得到热力学熔点约为1360～1380 K, 与实验结果1358 K吻合良好. 动力学系数定义为界面移动速度与过热程度的比值, 表现为明显的各向异性: k100=39 cm•s−1•K−1, k110=29 cm•s−1•K−1, k111=20 cm•s−1•K−1. k100与k110之间的比例符合collision-limited理论, (111)密排面有与其它低指数表面不同的熔化方式.     

热镀铜层冷凝过程的分子动力学模拟

During the hot-dip process of Cu on the surface of the steel,it involves the solidification from liquid to coating. The cooling rate has great influence on the microstructure and the performance. By means of constanttemperature,constant-pressure molecular dynamics simulation technique,the solidification process of the liquid model system made of 500 Cu particles has been studied with the period boundary condition. With the pairs analysis technology and the bond orientational order method,the difference of the structure and energy of the liquid Cu model system between different cooling velocities has been compared. The significant information of microcosmic structural transformation in the solidification process of liquid Cu system has been obtained. The calculation results show that the Finnis-Sinclair（FS）potential works very well in the solidification process of Cu. Cooling slowly the crystal copper layer can be obtained. Cooling quickly the amorphous copper layer can be obtained.     

金属Cu晶化与玻璃化行为的分子动力学模拟

A series of simulations of the crystallization and vitrification processes for metal Cu were carried out by means of the molecular dynamics technique. The radial distribution function, common neighbors, internal energy and volume of the system were recorded during the processes. The atomic internal energy, atomic Voronoi volume and atomic stress field of the relax system were analyzed at zero temperature. The interaction between atoms in the system is described using the embedded atom potential as proposed by Mishin. The simulation results show that crystalline and non-crystalline phases form at lower and higher cooling rates respectively. In comparison to nanocrystals, it is found that metallic glass has higher internal energy and larger volume. The intrinsic stress field is induced by distortion of the lattice.     

SrF2和BaF2熔化温度的分子动力学模拟

利用壳层模型分子动力学方法,考虑萤石结构分子中的预熔化现象,对SrF2和BaF2的分子动力学模拟熔化温度进行修正,获得了高压下SrF2和BaF2的熔化温度．同时给出了300K、0．1MPa-7GPa和10．1MPa-3GPa时SrF2和BaF2的状态方程,与已有研究结果的最大误差分别为0．3％和2．2％．计算所得SrF2和BaF2常压下的熔点与已有的实验结果符合较好．对于SrF2和BaF2分子体积变化和已有的熔化模拟的差别也做了比较和讨论．     

Melting Mechanism and Structure Evolution of Au Nanofilms Explored by Molecular Dynamics Simulations

The melting mechanism and structure evolution of two-dimensional Au nanofilms with different thicknesses have been investigated in detail by using classical molecular dynamics simulations. The simulation results demonstrate that all Au nanofilms display a two-stage melting behavior of surface premelting and homogenous melting. Furthermore, the premelting behavior only occurs in the outermost layers but the other inner layers always keep a stable solid state until the corresponding melting point, which is different from the premelting behavior from surface into the interior in zero-dimensional Au nanocluster and one-dimensional Au nanowire. Meanwhile, the increase of nanofilm thickness can lead to an increase of melting point. During the premelting process, the surface reconstruction fromthe f100g plane to the f111g plane has directly been observed at a atomic level for all Au nanofilms. However even for the thinnest L2 nanofilm, the surface stress can't induce such surface reconstruction until temperature is up to 500 K, while similar surface reconstruction induced by surface stress can be observed at much lower temperature for the Au nanowire due to its higher surface-to-volume ratios compared to the Au nanofilm. In addition, our simulation results show that the thinnest Au nanofilm with two atomic layers can be broken into independent one-dimensional nanowires when the temperature reaches a certain value.     

金属Cu液固转变及晶体生长的分子动力学模拟

采用分子动力学模拟研究了液态Ｃｕ在不同冷却速度下的凝固特点,模拟采用ＥＡＭ作用势,计算了不同温度,不同冷却速度下Ｃｕ的偶相关函数,结果表明ＥＡＭ作用势能很好地描述液态Ｃｕ的结构特征,当冷却速度较快时,液Ｃｕ形成非晶;当冷却速度较慢时,液Ｃｕ形成晶体,分析了不同冷却速度下体系的相变热力学及相变动力学过程,最后采用液固两层构型法,描述了Ｃｕ晶体的生长过程。