Material simulations with tight-binding molecular dynamics

Tight-binding molecular-dynamics has recently emerged as a useful method for atomistic simulation study of realistic materials. The method incorporates electronic structure calculation into molecular dynamics through an empirical tight-binding Hamiltonian and bridges the gap between ab initio molecular dynamics and simulations using empirical classical potentials. This article reviews some achievements and discusses some recent developments in materials simulations with tight-binding molecular dynamics.     

并行计算在机械加工领域中的应用

在精密加工中应用分子动力学仿真技术，存在仿真模型较小、计算速度太慢等问题，为此提出了并行分子动力学仿真技术，它是在原来的分子动力学仿真技术里面加入并行的思想，用并行的优势来弱化原仿真的劣势，可以扩大仿真规模，提高运算速度，使仿真模型更加接近于实际，从而促进超精密加工微观机理的研究。     

单晶材料纳米加工的分子动力学模拟研究进展

分子动力学模拟技术是纳米加工研究的重要方法之一。本文概述了经典分子动力学模拟的基本原理和方法,并结合分子动力学模拟的发展历程,从单晶材料纳米加工的物相转变、结构及热力学特性、介质的影响以及加工后亚表面变形层特性这5个方面,综述了分子动力学模拟在单晶材料纳米加工研究中的应用,最后分析了单晶材料分子动力学模拟中存在的一些问题及需要关注的方向。      

Cu和Al超高速精密磨削成屑机理研究

建立了超高速精密磨削分子动力学仿真的物理模型，合理选择了超高速精密磨削单晶铜和单晶铝的分子动力学仿真势函数。研究了超高速精密磨削分子动力学仿真的基本算法和步骤。对超高速精密磨削单晶铜和单晶铝的分子动力学仿真的结果进行了分析和研究，得出了超高速精密磨削单晶铜和单晶铝时工件所能获得的极限表面粗糙度。预测了超高速精密磨削单晶铜时工件表面变形层的极限深度和所能达到的极限加工精度。实验结果表明，最小磨削厚度是与磨削刃半径成比例的。     

A study on distribution of plastic region near a crack tip using three-dimensional molecular dynamics simulation

Molecular dynamics simulation is emerging with recent advent of high-performance computers. This paper addresses an application of molecular dynamics simulation to calculation of stress intensity factors (SIF) of a material using a three-dimensional molecular model. Since the popular molecular models such as Lennard-Jones model fails to compute behaviors of materials correctly, in this paper the embedded atomic model (EAM) was utilized. A copper plate with a single edge crack is considered to calculate SIFs in opening mode. More than ten thousand of molecules were used for the simulation and due to a large amount of computation, a super computer CRAY C90 was employed. The results show good agreement with the theoretical SIF values.     

Calculation of stress intensity factors using three-dimensional molecular dynamics simulation

Molecular dynamics simulation is emerging with recent advent of high-performance computers. This paper addresses an application of molecular dynamics simulation to calculation of stress intensity factors (SIF) of a material using a three-dimensional molecular model. Since the popular molecular models such as Lennard-Jones model fails to compute behaviors of materials correctly, in this paper the embedded atomic model (EAM) was utilized. A copper plate with a single edge crack is considered to calculate SIFs in opening mode. More than ten thousand of molecules were used for the simulation and due to a large amount of computation, a super computer CRAY C90 was employed. The results show good agreement with the theoretical SIF values.     

模拟位错斑图的元胞自动机与分子动力学模型

建立了一个模拟位错斑图形成的元胞自动机-分子动力学模型，该模型考虑了在相同或不同滑移面上具有相反Burgers矢量方向的刃型位错间的长程与短程相互作用，采用分子动力学方法处理长程相互作用，采用元胞自动机方法处理短程相互作用，应用这个模型，模拟了在没有外加应力和存在外加循环应力条件下的Cu单晶的位错结构。     

Atomistic Modeling of Solidification Phenomena Using the Phase-Field-Crystal Model

In recent years, a fundamental understanding of solidification and its behavior has been gained through molecular dynamics simulations and the phase-field method, the first of which is limited to short time scales and the latter of which does not represent interface and elastoplastic properties accurately. Recently, the phase-field-crystal (PFC) method, a continuum method operating on atomistic length scales and diffusive time scales, has helped bridge the multiple scale gap between molecular dynamics and phase field. This review surveys the advances of PFC models in the context of various solidification phenomena.     

On the mechanics of single-walled carbon nanotubes

This review paper discusses some basics in using continuum mechanics and molecular dynamics to characterize the deformation of single-walled carbon nanotubes (SWCNTs). It identifies that the van der Waals force between SWCNTs in a bundle distributes symmetrically and influences the bundle formation, and that to avoid misleading results from a molecular dynamics simulation, the interaction potential, thermostat scheme and simulation parameters must be carefully selected. The paper then points out that when the necessary condition proposed by Vodenitcharova and Zhang and a compatibility condition for elastic constants are satisfied, the intersect of the bending and in-plane stiffness curves in the modulus-thickness plane can determine a unique effective wall thickness of an SWCNT and hence its Young's modulus.     

分子动力学在材料科学中的应用

分子动力学方法是进行物质原子或分子层次计算机模拟时所采用的一种基本方法。通过分子动力学模拟，可以给出原子尺度上材料及其演化过程细节的可能性，具有无先例的准确性，使材料设计和性能预测成为可能。本文分析了分子动力学模拟的基本原理和算法；综述了分子动力学在材料科学中的应用，介绍了最近发展的第一原理分子动力学模拟，指出材料科学中第一原理分子动力学模拟的应用还有待进一步发展。     

概述经典分子动力学模拟计算

综述了分子动力学模拟技术的发展,介绍了经典分子动力学的基本思想、有关的有限差分技术、原子间作用势及参数的确定、初始条件和边界条件的选取、平衡态系综及其调控、感兴趣量的提取,最后还指出了分子动力学模拟方法本身进一步发展的方向。     

Prediction of cutting forces in the micro-machining of silicon using a “hybrid molecular dynamic-finite element analysis” force model

The study and development of micro-machining technology has been an area of ongoing focus for numerous researchers. Interest in this topic has been increasing over the past decade due to the trend towards higher accuracy, smaller-sized components. Linking material property acquisition and modelling in the nanometric scale with those on the micro-scale is a considerable challenge in material science in general and in micro-machining in particular. Due to computational limitations it is presently extremely difficult to inflate atomic level models and simulations to the micro-sized component dimensions. This detailed knowledge of material behaviour will provide the necessary insight to support process development, modelling and the optimization of critical ultra-precision machining processes. This paper presents a new methodology of providing a finite element model of the micro-cutting process with relevant material properties acquired from a newly developed molecular dynamics simulation model of a uniaxial tension test performed on silicon. Material properties such as yield stress, ultimate stress and modulus of elasticity are extracted from the stress–strain curve produced by the molecular dynamics model and automatically fed to the finite element model to evaluate the cutting forces required to machine a silicon wafer using different cutting parameters.     

Molecular Dynamics Study of the Deformation Processes of Metallic Materials in Structural and Phase (Martensitic) Transformations

The application of the method of molecular dynamics based on the use of pair interatomic potentials has been discussed to study various deformation processes during structural and phase (martensitic) transformations in metallic single and polycrystals. It has been shown that the method of molecular dynamics in a two-dimensional model makes it possible to qualitatively analyze the processes of grain-boundary sliding and other mechanisms of plastic deformation in polycrystals. It is also an efficient tool for describing diffusionless martensitic transformations in metallic materials. As an example, the use of the method for simulating grain-boundary sliding in a polycrystal with nonequilibrium grain boundaries is presented and the mechanisms of overcoming an obstruction in the form of a protruding segment of a grain have been demonstrated at the atomic level. The application of this method for describing the dynamics and morphology of the thermoelastic martensitic transformation has been illustrated by the example of the titanium nickelide and manganese alloys.     

Physical Characteristics of Friction Processes in a Columnar Approach-Separation Model with Tangential Force

Protection of Metals and Physical Chemistry of Surfaces - Three-dimensional molecular dynamics (MD) simulation is conducted to understanding the dynamics processes of atomic-scale friction, which...     

Behavior of dopant-modified interfaces in metallic nanocrystalline materials

This article provides a concise discussion of thermodynamic and kinetic contributions to microstructure stabilization by dopant atoms located at interfaces in metallic nanocrystalline materials and an overview of recent molecular dynamics simulations used to study the behavior of dopant-modified interfaces in nanocrystalline copper. Molecular dynamics simulations show that antimony dopant atoms randomly positioned at copper grain boundaries can retard grain growth, in agreement with proposed thermodynamic and kinetic predictions. Simulations of uniaxial tensile deformation show a maximum in the flow strength at a grain size of 15 nm and that antimony dopants at the grain boundaries do not appreciably impact the nucleation of partial or full dislocations during uniaxial tensile deformation in nanocrystalline copper.     

Concerning the Data of Numerical and Physical Experiments in Studying the Adsorption of Gas and Vapors in Micropores of Active Carbons

Protection of Metals and Physical Chemistry of Surfaces - The conditions for carrying out molecular dynamics calculations of adsorption isotherms of gases and vapors in micropores of active carbons...     

基于分子动力学结合神经网络的Au表面能计算方法

利用嵌入原子模型,采用分子动力学方法计算了贵金属Au低指数晶面及部分简单高指数晶面的表面能.同时,采用Levenberg-Marquardt算法,建立了Au表面能的BP神经网络模型;结合分子动力学模型的计算数据,通过大量数据的自学习训练,完成神经网络模型对Au高指数晶面表面能的预测.计算结果表明:该方法具有较高的预测精度,能正确预言低指数晶面表面能的排序,Au各晶面的表面能随其晶面与(111)密排面夹角的增大呈现先增大后减小的特点.     

基于临界晶胚法的Ni固液界面能分子动力学计算

使用分子动力学法,研究不同半径的Ni晶胚在其液相中的生长及熔化行为。研究发现,一定半径的晶胚存在临界形核温度,高于这个温度,晶胚生长;低于这个温度,晶胚熔化,并且临界形核温度与晶胚半径的倒数成线性关系,这和经典形核理论以及Gibbs-Thomson模型的描述一致。基于临界晶胚演化的分子动力学模拟方法得到了金属Ni的Gibbs-Thomson系数为1.56×10-7K·m,并获得了Ni的固液界面能为0.211J/m2,结果与实验测量值一致。     

Molecular Dynamic Calculations of the Adsorption Equilibrium of Gas Mixtures in Micropores of Active Carbon and on Graphene Surfaces

Protection of Metals and Physical Chemistry of Surfaces - As an addition to previously obtained data, it has been shown that the adsorption isotherms calculated by the molecular dynamics method for...     

3,5-二溴水杨醛-2-噻吩甲酰肼席夫碱缓蚀剂在油田水中对碳钢的缓蚀性能及分子动力学模拟

合成了一种新的席夫碱缓蚀剂3,5-二溴水杨醛-2-噻吩甲酰肼(L2),通过Tefel极化曲线、电化学阻抗、扫描电镜和分子动力学模拟方法研究了该缓蚀剂在模拟油田水中对碳钢的缓蚀效果,并探讨了其缓蚀机理和吸附行为。结果表明,L2在不同温度、H2S浓度、pH值和Cl-浓度条件下的模拟油田水中对碳钢均具有良好的缓蚀性能。分子动力学模拟结果表明,在水溶液中缓蚀剂L2分子可以稳定地平行吸附在金属表面,有效地将金属表面和水分子隔开,从而起到缓蚀作用,吸附方式为多位点化学吸附;同时L2形成的分子吸附膜可有效地抑制腐蚀离子(Cl-和H3O+)在吸附膜中的扩散,避免了金属表面与腐蚀介质接触而发生腐蚀,从而表现出良好的缓蚀性能。