分子动力学模拟不同入射能量的SiF2与SiC的相互作用

采用分子动力学模拟方法研究了入射能量对SiF2与SiC样品表面相互作用的影响。本次模拟选择的入射初始能量分别为0.3,1,5,10和25 eV。模拟结果显示SiF2分解率与Si和F原子的沉积率有密切的关系。沉积的Si和F原子在SiC表面形成一层SixFy薄膜。随入射能量的增加,薄膜厚度先增加后减小,薄膜中Si-Si键密度增大。构成薄膜的主要成分SiFx(x=1~4)中主要是SiF和SiF2,随入射能量的增加,薄膜成分由SiF2向SiF转变。     

分子动力学模拟Gd原子在Cu低密勒表面的扩散过程

为了分析Gd吸附原子在Cu（001）、Cu（110）和Cu（111）表面的扩散机制，本文用分子动力学对该扩散过程进行模拟。模拟结果表明在Cu（001）和Cu（111）表面，Gd原子通过跳跃机制扩散；在Cu（110）表面，在[110]方向Gd原子通过跳跃机制扩散，而且多步跳跃频率很高，而在[001]方向则通过交换机制扩散。通过对扩散频率的拟合，发现在各种扩散机制都符合Arrhenius公式，从而确定了在Cu（001）和Cu（111）表面扩散势垒分别为0．19eV和0．013eV，在Cu（110）表面，沿[110]方向跳跃扩散势垒和沿[001]方向交换扩散势垒分别为0．097eV和0．33eV。     

金属钛拉伸的分子动力学研究

本文利用分子动力学的研究方法,采用了钛的嵌入式原子势,建立了沿[0001]晶向和[0110]方向拉伸模型,结果表明:两种方向的拉伸均包含弹性变形阶段、屈服阶段、颈缩阶段、断裂阶段.沿[0001]方向拉伸时,滑移系少,取向偏离软取向.变形时屈服强度为3.55GPa,屈服应变为0.063,断裂时的应变达到0.55.沿[01...     

无定形 Si-B-C体系扩散行为分子动力学模拟

用分子动力学方法研究了不同温度下无定形Si—C、Si—B—C体系的扩散行为，分析掺杂B原子对体系热稳定性及高温抗蠕变性的影响．基于UFF力场，在300、773、1273、1773及2073K下，用分子动力学方法计算并比较了它们的MSD曲线及扩散系数，分析温度对原子自扩散的影响．无定形体系引入B原子后，原子自扩散系数降低；随温度升高，自扩散系数缓慢上升，接近2073K附近B原子的自扩散有明显加速趋势，说明体系能够在2073K以下不发生相分离，保持热稳定及良好的高温抗蠕变性．     

Molecular Dynamics Simulation for Ultrafine Machining

This article surveys the advances of molecular dynamics (MD) simulation in the research of ultrafine machining and related technologies. Modeling methods, including interatomic potentials and boundary conditions, are addressed. Algorithm strategies for MD simulations are discussed. By applying simulations with Tersoff potential, a case study of the material removal mechanism of the polishing based on coupling vibrations of liquid (PCVL) is presented.     

Silver Diffusion and Clustering in Oxyfluoride Glasses Investigated by Molecular Dynamics Simulations

Glasses with compositions (97 – x)[PbF₂:GeO₂]–3Al₂O₃–xAg₂O, with the PbF₂:GeO₂ ratio equals to 1.5 and x varying from 0 to 3%, form silver surface films after thermal treatment near the glass transition temperature. The NPT molecular dynamics simulations of a glass composition 56.4PbF₂–37.6GeO₂–3Al₂O₃–3Ag₂O have been performed, where 0, 20, 40, 60, and 100% of the Ag⁺ ions were reduced to Ag by the fluoride ions. The simulations showed that the silver atoms aggregate into clusters of increasing numbers and sizes as the silver atoms content increases. In addition, the silver atoms diffusion coefficients are at least one order of magnitude larger than the fastest ion in the matrix. These results are consistent with the rapid formation of the metallic surface film observed experimentally.     

MoS2基板上外延生长C60薄膜的分子动力学模拟

外延生长异质薄膜通常要求材料之间晶格匹配 ,然而利用范德瓦尔斯作用外延生长时 ,晶格匹配要求显著降低。实验上已经得出了在MoS2 基板上外延生长C60 薄膜的结果 ,本文用分子动力学计算机模拟方法对MoS2 基板上外延生长C60 薄膜进行了研究 ,证实范德瓦尔斯外延可以克服较大的晶格失配问题。     

聚变堆中H刻蚀碳氢薄膜的分子动力学模拟

使用分子动力学方法模拟了低能H原子与碳氢薄膜的作用过程,以了解基于核聚变装置中等离子体与C基材料的相互作用机制。模拟中使用REBO(reactive empirical bond order)势函数来描述C-H体系中原子间的相互作用,并使用Berendsen热浴来控制体系的温度。文中着重探讨了入射能量对低能H原子刻蚀碳氢薄膜的影响,入射能量分别为0.3,1,5和10eV。模拟结果显示随着入射能量的增加,H原子的吸附率增加,C原子和H原子的刻蚀率增加。同一能量下H原子比C原子更易发生刻蚀。通过讨论发现在H原子与碳氢薄膜作用过程中,当能量大于1 eV时,由于入射的H原子先沉积在表面并与表面原子发生反应形成碳氢化合物,然后在后续入射粒子的轰击下碳氢化合物在表面发生解吸附现象,从而导致了C原子的刻蚀,因此C原子的刻蚀发生主要是化学增强的物理溅射。     

碳纳米管内气体吸附与扩散的分子模拟研究

气体在纳米管中的输运具有非连续性的特点,这与宏观条件下稀薄气体的输运类似,同时考虑到纳米管的比表面积非常大,那么吸附气体对输运的贡献就不可忽略。本文基于平衡分子动力学和巨正则蒙特卡洛方法,模拟了不同气体分子在不同直径碳纳米管内的扩散和吸附行为。运用通量相关函数计算了气体的输运扩散系数,并结合稀薄气体动力学推导出了气体的表面扩散系数。结果表明,气体在碳纳米管中的输运扩散系数比克努森公式计算出的结果高数倍甚至十数倍,碳纳米管内吸附分子的表面扩散是气体快速输运的原因,表面扩散系数随表面覆盖度的增大而增大。     

分子动力学模拟样品温度对F刻蚀SiC的影响

利用分子动力学模拟方法研究了在低能F原子刻蚀SiC表面过程中样品温度对刻蚀的影响。由模拟结果可知,随着温度的升高,F在样品表面的沉积量和散射量均呈下降趋势,而发生溅射的F的量和与样品作用生成挥发物质的F的量逐渐增加。Si的刻蚀量均随着温度的升高而升高。样品中Si原子的刻蚀主要是通过生成SiF4得以实现的,C原子的刻蚀主要是通过生成CFx(x=1～3)等挥发性物质实现的。     

Molecular Dynamics Simulation on Diffusion of Five Kinds of Chemical Additives in Polypropylene

Molecular dynamics (MD) simulation was used to investigate the diffusion behaviour of five additives [2,6‐di‐tert‐butyl‐4‐methylphenol (BHT), 2‐(2‐Hydroxy‐5‐methylphenyl)benzotriazole (UV‐P), 2,4‐Di‐tert‐butyl‐6‐(5‐chloro‐2H‐benzotriazol‐2‐yl) phenol(UV‐327), 2‐(2H‐benzotriazol‐2‐yl)‐4‐(1,1,3,3‐tetramethylbutyl) phenol (UV‐329) and 2‐hydroxy‐4‐(octyloxy)benzophenone (UV‐531)] in polypropylene (PP) at the temperature of 293, 313 and 343 K. The diffusion coefficients were determined through Einstein relation connecting the data of mean square displacement at different times. The simulated diffusion coefficients were compared with that predicted by Piringer model and by experiments to evaluate the accuracy of MD simulation technique for estimating the diffusion coefficients of chemical additives in PP. Results showed that the simulated values were generally within one order of magnitude of the corresponding experimental values. The activation energies of additives were calculated by plotting the logarithm of diffusion coefficients versus the reciprocal of temperature according to Arrhenius equation. The activation energies calculated from MD simulation were also more closely to experimental values. Subsequently, the diffusion mechanism of additives inside PP was tentatively explored by analysing the interaction energy between diffusion molecules and polymer, free volume, molecular weight, size and shape, and the mobility of polymer chain. The movements of the additives in PP cell models at different simulation time suggested that for a long time, the additive molecules vibrate rather than hopping until they find the equal or larger transport channel to diffuse. It is demonstrated that the MD simulation may be a useful approach for predicting the microstructure and the diffusion coefficient of chemical additive with large molecular size and complex structure in polypropylene. Copyright © 2017 John Wiley & Sons, Ltd.     

饱和液态制冷剂氨的热物理性质的分子动力学模拟

运用分子动力学方法模拟了制冷剂氨的饱和液态热物理性质。采用典型的site-site势能模型模拟了制冷剂氨的饱和液态密度和比焓,将模拟结果与美国国家标准研究所(NIST)数据库的值进行了对比,最大相对偏差分别在1.5%(密度)以内和3.2%(比焓)以内。对比结果表明:采用合理的势能模型和参数,运用该模拟方法预测单一组分工质的热物理性质是可行的。     

分子动力学模拟噻吩/正庚烷在PEG膜中溶解-扩散行为

采用分子动力学方法模拟汽油组分在聚乙二醇(PEG)膜中的溶解-扩散行为。吸附动力学模拟结果表明,动力学平衡之后,噻吩与聚合物表面距离明显缩短。PEG对噻吩与正庚烷的吸附能分别为-52.17 kJ/mol和-38.00 kJ/mol。PEG对噻吩的吸附能小于正庚烷,因而PEG对噻吩具有吸附选择性。扩散动力学模拟结果表明,在不同温度下,噻吩的扩散系数均高于正庚烷,PEG对噻吩具有扩散选择性,与实验结果相符。     

入射角度对Ar~+与SiC表面相互作用影响的分子动力学模拟

采用分子动力学模拟方法研究了入射角度对Ar+与SiC样品表面相互作用的影响。由模拟结果可知,入射角度对样品原子溅射影响很大。随着入射角度的增大,Si原子和C原子的溅射量先增加后减小。相同入射角度下,Si原子的溅射阈值比C原子的小,Si原子的溅射量大于C原子的溅射量。初始样品在Ar+以不同角度轰击2000次后的形貌各异。产物中主要以Si原子和C原子为主,有少量的Si类和C类产物。入射角度对产物Si原子的角度分布几乎没有影响,而对产物C原子的角度分布有较小的影响。     

Molecular Dynamics Simulation of Porous Layer-enhanced Dislocation Emission and Crack Propagation in Iron Crystal

The internal stress induced by a porous layer or passive layer can assist the applied stress to promote dislocation emission and crack propagation, e.g. when the pipeline steel is buried in the soil containing water, resulting in stress corrosion cracking (SCC). Molecular dynamics (MD) simulation is performed to study the process of dislocation emission and crack propagation in a slab of Fe crystal with and without a porous layer on the surface of the crack. The results show that when there is a porous layer on the surface of the crack, the tensile stress induced by the porous layer can superimpose on the external applied stress and then assist the applied stress to initiate crack tip dislocation emission under lowered stress intensity KI, or stress. To respond to the corrosion accelerated dislocation emission and motion, the crack begins to propagate under lowered stress intensity KI, resulting in SCC.     

Investigation in Influence of Types of Polypropylene Material on Diffusion by Using Molecular Dynamics Simulation

Polypropylene (PP) and its copolymers are widely used in food packaging films and containers. This paper investigates the diffusion of limonene as a low molar mass compound through three types of polypropylene materials (PP‐H, PP‐B and PP‐R) by using the molecular dynamics method, evaluates the influence of types of polypropylene material on the diffusion behaviour of limonene and reveals the diffusion mechanism. The diffusion coefficients of limonene in PP‐H, PP‐B and PP‐R are obtained at 313K and 353K. The accessible free volumes for polymers PP‐H, PP‐B and PP‐R are calculated by using the probe radius r_p = 0.09, 0.11, 0.128 and 0.209 nm, respectively. The results suggest that not only the amount of accessible free volume in PP‐R cell model is larger than that of PP‐H and PP‐B but also the free volume in PP‐R connects together to form some larger free volume clusters. The movements of the limonene molecules through the PP‐H, PP‐B and PP‐R cell models at different simulation time suggest that for a long time the limonene molecules squirm slowly in the polymer cell rather than jumping and that the hopping diffusion is not suitable to explain the diffusion of limonene in polypropylene. The movement trajectories of the limonene molecules in PP‐R indicate that the movements of limonene in PP‐R are more active than that in PP‐H and PP‐B. The paper reveals the diffusion dynamics process and microscopic mechanism of small molecules from different types of polypropylene. Copyright © 2011 John Wiley & Sons, Ltd.     

材料科学中的分子动力学模拟研究进展

本文综述了几种常见条件下的分子动力学模拟方法以及分子动力学模拟的最新发展趋势，介绍用分子力学模拟方法研究固体的体相结构，表面问题，界面问题以及薄膜形成过程等方面的研究成果。     

聚醋酸乙烯酯与黑索今体系的分子动力学模拟

聚醋酸乙烯酯(PVAc)与黑索今(RDX)的界面相互作用会直接影响RDX的表面包覆效果,因此,在原子、分子层次研究其作用方式,可以发现相互作用机制。利用分子动力学模拟方法,以径向分布函数描述组分间相互作用的方式;研究不同温度下PVAc与RDX晶面的相互作用,并计算PVAc在RDX晶体表面的扩散速率。结果表明,在298~353 K温度下,PVAc与RDX的结合能随温度升高略有降低;通过对有效各向同性模量和柯西压的分析得到,加入PVAc能够有效改善RDX的力学性能。此外,在343 K的温度下,PVAc在RDX表面的扩散速率最大,体系的力学性能最为优异。     

Na20-- A1203 -- SiO2微晶玻璃体系熔体结构的分子动力学模拟

采用分子动力学方法模拟了7种组分的Na20-- A1203 -- SiO2体系微晶玻璃熔体结构,分析了体系的径向分布函数、键长分布和键角分布,得出了不同含量Na＋对Na20-- A1203 -- SiO2体系玻璃网络结构的影响。     

基于分子动力学方法模拟硅功能化石墨烯纳米压痕过程

基于分子动力学方法, 采用Tersoff势函数与Lennard-Jones势函数, 结合速度形式的Verlet算法, 首先对单层石墨烯薄膜的分子动力学模型进行了纳米压痕力学过程的模拟.通过模拟得到单层石墨烯薄膜的荷载-位移曲线, 并对其进行最小二乘法拟合, 得到了单层石墨烯薄膜的弹性模量和强度, 通过和已有研究结论进行对比, 验证了模型的有效性.最后建立了由双层石墨烯薄膜构成的硅功能化石墨烯分子动力学模型, 进行了纳米压痕力学过程的模拟.采用同样的计算方法和过程, 得到了硅碳比 (硅原子数与碳原子数之比) 为0.65%的双层硅功能化石墨烯材料的弹性模量和强度分别为0.98 TPa和247.33 GPa.