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.     

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.     

金属铜升温熔化过程的分子动力学模拟

采用分子动力学方法模拟了金属铜的升温熔化过程.原子间作用势采用FS (Finnis-Sinclair)势，结构分析采用双体分布函数(PCF)、均方位移(MSD)等方法.计算结果表明,在连续升温过程中，金属铜在1444 K熔化，在该熔化点的扩散系数为4.31×10－9 m2•s－1.上述结论与实验值相当接近，并且比之采用EAM镶嵌原子势所作模拟得到的结果更佳，说明FS势可以用来处理象液铜这样较复杂的无序体系.本文指出了升温速率在金属熔化过程中所起的作用.     

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.     

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.     

激光诱导铝纳米膜熔化机理的分子动力学模拟

采用耦合一维双温模型的分子动力学方法研究了纳米级的铝膜在飞秒激光辐照下的熔化机制.这种方法不仅能够在原子水平上展现金属膜的各种微观行为,还能有效地描述金属膜的激光能量吸收、传递和金属电子热传导等过程.模拟结果表明,与其它金属相比,铝膜在飞秒激光辐照下的电子温度、晶格温度以及内部压力等呈现出不同的变化.铝膜在较高强度激光辐照下会很快发生全局一致的熔化,这与镍膜上下非均匀的熔化不同.并且由于铝的电子-声子耦合强度较高导致铝膜较镍膜和金膜熔化得更快.模拟结果显示,铝膜的熔化时间与实验测量的超快激光诱导的铝膜熔化时间一致.进而从理论上支持激光诱导的铝膜熔化是一个热力学熔化过程.     

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。     

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.     

MgSiO3状态方程的分子动力学模拟

The equation of state of MgSiO3 perovskite under high pressure and high temperature is simulated using the molecular dynamics method. It was found that the molecular dynamics simulation is very successful in accurately reproducing the measured molar volumes of MgSiO3 perovskite over a wide range of temperatures and pressures. The simulated equation of state of MgSiO3 perovskite matched experimental data at up to 140GPa at 300 K, as well as the fitting data of others and results from the first-principles simulation based on the local density approximation. The simulated equations of state of MgSiO3 perovskite at higher temperatures and higher pressures also correspond to the other calculations. In addition, the volume compression data of MgSiO3 perovskite is simulated up to 120 GPa at 300, 900, 2000 and 3000 K, respectively.     

熔融ZnCl2结构的分子动力学模拟研究

熔融ZnCl2作为一种离子性共价性参半的典型熔盐, 其近邻结构在实验测量和分子动力学模拟方面均作过一些研究。本文依据新近EXAFS实验结果, 比较了不同的有效势下模拟得到的径向分布函数,表明KDR势可作为一种实用势。并进一步在KDR势模拟产生的瞬态构型基础上, 使用键序参数方法研究了晶态和熔融态ZnCl2中的近邻结构。结果表明, 和晶态ZnCl2一样, 在熔融ZnCl2中存在稳定的Zn/Cl正四面体结构, 但熔态和晶态Zn/Cl近邻结构热波方差σ不同。计算表明300K晶态σ=5.0℃, 613K熔融态σ=12.2℃。也对熔融ZnCl2的网络状结构和宏观输运性质进行了讨论。     

离子液体[emim]Br熔点的分子动力学模拟

运用分子动力学模拟, 采用直接加热法和微正则(NVE)系综法计算离子液体[emim]Br的熔点, 以期获得较好的熔点预测方法. 直接加热法通过分析体系的非键合能、密度、径向分布函数、扩散系数和平动序参数随温度的变化关系判断熔点; NVE系综法则通过获得固液共存体系判断熔点. 直接加热法中, 体系易出现过热问题; NVE系综法则能有效克服过热问题, 是在模拟研究中应优先选择的离子液体熔点预测方法.     

Molecular Dynamics Simulations of Silica Nanotube: Structural and Vibrational Properties Under Different Temperatures

Four-, six-, and eight-membered ring silica nanotubes at temperatures from 300 K to 1600 Kare relaxed by classical molecular dynamics simulations with three potential models. Thesimulation results indicate that the stability of the end rings of the three silica nanotubes gradually decreases with increase in temperature. The validity of the vibrational features of silica nanotubes is shown by the vibrational density of states. Infrared spectra on the silica nanotubes under different temperatures are investigated. A detailed assignment of each spectral peak to the corresponding vibrational mode of the three nanotubes has been addressed. The results are in good agreement with the other theoretical and experimental studies.     

RbCl熔解的分子动力学模拟研究

采用等压分子动力学模拟方法，研究了从晶相到液相不同温度下ＲｂＣｌ体系的结构和性质，等压模拟咄等容怀致的平衡性质和结构特征，键序参数计算，不计及导热过程情形下，体系在振荡驰豫时间量级内完成熔化过程，由于不需要密度数据，等压模拟有望发展成为材料设计中的一种手段。     

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.     

甲硫氨酸-脑啡肽的分子动力学模拟

The conformational properties of Met-enkephalin (Tyr-Gly-Gly-Phe-Met) were investigated by high temperature quenched molecular dynamics simulations in vapor. Each of these selected structures were then analyzed according to their backbone(φ,Ψ) conformational distributions and sorted into 13 families by computing the rms difference between the Cα-C backbone fragments of each residue over all the structures. Selected lowest energy conformations from each of 13 families were thoroughly energy minimized. The results of simulations show that Met-enkephalin is a flexible molecule. It shows a type Ⅰβ-turn, with the Gly2 carbonyl forming a hydrogen bond with the Met5 amino proton and a type Ⅱβ turn, with the Tyr1 amino proton forming a hydrogen bond with the Phe4 carbonyl. The multiple fit were carried out for all of the 13 conformers with morphine(9 atoms on the pharmacophore groups). F2 and F6 were the most similar to morphine. The rms were 0.0504 nm and 0.0726 nm. The results of simulations also show that Tyr amino N corresponds to N on piperidine ring in morphine, Tyr phenol corresponds to the phenol in morphine, the aromatic ring of Phe corresponds to the cyclohexene ring in morphine. The distances between the three pharmacophores, d1 (Tyr N to Tyr OH), d2 (Tyr N to Tyr du1), d3(Tyr N to Phe du2) and d4(Tyr N to Phe du2) were found to be about 0.8, 0.5, 0.7-0.9 and 0.5 nm, respectively, the corresponding, distances of morphine were found to be 0.7697(N18 to O6),0.5143(N18 to du25), 0.3962(N18 to du24)和0.5566(N18 to O15)nm. Therefore, they may be acted on the same receptor. This model should aid in pharmaceutical design of peptide and nonpeptide ligands with opioid.