温度对吡啶离子液体性质影响的分子动力学模拟研究

运用分子动力学模拟方法研究了温度对三种吡啶离子液体[BPy][BF4]、[HPy][BF4]、[OPy][BF4]热力学性质的影响, 得到了每个体系的密度、自扩散系数、电导率和黏度等. 研究结果表明: 随着温度升高, 同一种离子液体的密度减小, 阴阳离子的自扩散系数明显增大, 电导率升高, 而黏度降低. 在同一温度下, 随着阳离子上烷基链的增长, 离子液体的密度减小, 但热力学性质的变化规律并不完全同步. 烷基链长最短的[BPy][BF4]的自扩散系数和电导率在每个温度下均为最大, 而黏度最小; 但烷基碳链更长的[OPy][BF4]和[HPy][BF4]的各种性质相差不大,甚至当温度大于323K时, 烷基链较长的[OPy][BF4]的自扩散系数比[HPy][BF4]的大.     

温度对吡啶离子液体性质影响的分子动力学模拟研究

运用分子动力学模拟方法研究了温度对三种吡啶离子液体[BPy][BF_4]、[HPy][BF_4]、[OPy][BF_4]热力学性质的影响,得到了每个体系的密度、自扩散系数、电导率和黏度等.研究结果表明:随着温度升高,同一种离子液体的密度减小,阴阳离子的自扩散系数明显增大,电导率升高,而黏度降低.在同一温度下,随着阳离子上烷基链的增长,离子液体的密度减小,但热力学性质的变化规律并不完全同步.烷基链长最短的[BPy][BF_4]的自扩散系数和电导率在每个温度下均为最大,而黏度最小;但烷基碳链更长的[OPy][BF_4]和[HPy][BF_4]的各种性质相差不大,甚至当温度大于323 K时,烷基链较长的[OPy][BF_4]的自扩散系数比[HPy][BF_4]的大.     

Molecular dynamics study of particle emission by reactive cluster ion impact

Molecular dynamics (MD) simulations of sputtering process with fluorine cluster impact onto silicon targets were performed. By iterating collisional simulations on a same target, accumulation of incident atoms and evolution of surface morphology were examined as well as emission process of precursors. When (F₂)₃₀₀ clusters were sequentially irradiated on Si(1 0 0) target at 6 keV of total incident energy, column-like surface structure covered with F atoms was formed. As the number of incident clusters increased, sputtering yield of Si atoms also increased because the target surface was well fluoridised to provide SiF_x precursors. Size distribution of emitted particles showed that SiF₂ was the major sputtered particle, but various types of silicon-fluoride compounds such like Si₂F_x, Si₃F_x and very large molecules consists of 100 atoms were also observed. This size distribution and kinetic energy distribution of desorbed materials were studied, which showed that the sputtering mechanism with reactive cluster ions is similar to that under thermal equilibrium condition at high-temperature.     

金原子纳米团簇的负热容现象的分子动力学模拟研究

文中采用微正则分子动力学方法模拟研究了原子数N=60到675之间的6种金原子纳米团簇从固态到液态的熔解过程,得到了势能和热容量随温度的变化关系.其结果表明,所模拟的6种团簇在熔点附近出现负热容,通过对这些团簇熔解前后的势能以及结构变化的分析,探讨了产生负热容的微观机制.     

Quantum molecular dynamics simulation for fragmentation of arginine molecule induced by ion impact

15 keV Ga⁺ ion impact and the thermal decomposition of arginine molecules has been simulated by quantum molecular dynamics (QMD). We obtained the calculated mass spectra which express the distribution for fragment molecule generated by ion impact or thermal decomposition. From the comparison between the experimental TOF-SIMS spectra and the calculated spectra, we discussed the fragmentation mechanism of arginine molecule by Ga⁺ ion impact.     

用FS多体势模型模拟金属铜的冷却过程

采用常温、常压分子动力学模拟方法模拟了在周期性边界条件下由500个原子构成的液态Cu模型系统的凝固过程,考察了不同降温速率下液态Cu的凝固行为.模拟结果很好地重现了实验值.模拟中原子间作用势采用FS势,结构分析采用双体分布函数、对分析技术、内能、均方位移等方法,得到了原子体系微观结构组态变化的重要信息,并利用能量分析的方法对体系微观结构的变化进行了说明.     

Pt(111)表面低能溅射现象的分子动力学模拟

利用嵌入原子方法的原子间相互作用势，通过分子动力学模拟，详细研究了贵金属原子在Pt (111)表面的低能溅射现象.模拟结果显示：对于垂直入射情况，入射原子的质量对Pt (11 1)表面的溅射阈值影响不大.当入射原子的能量小于溅射阈值时，入射原子基本以沉积为主 ；当入射原子的能量大于溅射阈值时，溅射产额随入射原子能量的增加而线性增大；当入射 原子能量达到200 eV时，各种入射原子的溅射产额都达到或接近1，此时入射原子主要起溅 射作用.溅射原子发射的角分布概率和溅射花样与高能溅射相类似.研究表明：与基于二体碰 撞近似的线性级联溅射理论不同，当入射原子能量大于溅射阈值时，低能入射原子的溅射产 额正比于入射原子的约化能量和入射原子与基体原子的质量比.通过对低能入射原子的钉扎 能力分析，提出了支配低能溅射的入射原子反射物理机理. 关键词： 分子动力学模拟、低能溅射     

Time evolution of average rotation axis directions and mean rotation angles of pressurized liquid methyl iodide by molecular dynamics simulation

The rotational motion of liquid methyl iodide has been modelled by molecular dynamics simulations under input parameters optimized from literature values to yield the experimental enthalpy of vaporization and permanent dipole moment of the molecule. First, it is shown that results describing the correlation function of the tumbling motion of the molecules agree reasonably well with some corresponding findings from a spectroscopic Raman study. Second, the rotational motion involving the spinning component around the molecule's symmetry axis was simulated, an effect inaccessible by experiment. Third, and most relevant to the author's interests, a group-theoretical formalism was used that generates the time evolution of the average direction of the average rotation axis as well as the mean rotation angle around it. This approach allowed a more realistic understanding of the effects of density and temperature on molecular rotational motion, as well as a better quantification of the influence of short-time inertial decay, than the common approach of studying orientational correlation data along permanently molecule-fixed axis directions. Fourth, site–site radial distribution functions between neighbouring molecules were simulated, establishing a shielding effect that prevents a carbon atom from approaching any other site by their closest distance.     

Computation of some thermodynamics, transport, structural properties, and new equation of state for fluid methane using two-body and three-body intermolecular potentials from molecular dynamics simulation

Molecular dynamics simulation has been performed to obtain pressure, radial distribution function, and self-diffusion coefficient of fluid methane using one site OPLS (optimized potentials for liquid simulations), five sites OPLS-SITE, and two-body HFD (Hartree-Fock dispersion)-like potentials. To take higher-body forces into account, three-body potential of Hauschild and Prausnitz (1993) has been used with the two-body HFD-like potential. The significance of this work is that the three-body potential of Hauschild and Prausnitz extended as a function of density and temperature and used with the HFD-like potential to improve the prediction of the results of pressure of fluid methane without requiring an expensive three-body calculation. The molecular dynamics simulation of methane has been also used to determine a new equation of state. The results are in a good agreement with experimental and theoretical values.     

Study on the relations of sensitivity with energy properties for HMX and HMX-based PBXs by molecular dynamics simulation

Molecular dynamics simulation was applied to study the structure and energy properties of β-HMX (β-cyclotetramethylene tetranitramine) crystal and its composite PBXs (polymer-bonded explosives) with F₂₃₁₁ as a polymer binder under different temperatures and F₂₃₁₁ concentrations. The interface interaction energy of HMX and F₂₃₁₁, the interaction energy E_N–N between N atoms in N–NO₂ trigger bond in HMX molecules, and the cohesive energy density (CED) are presented and analyzed. A meaningful finding is that there exists correlation between E_N–N and the sensitivity of β-HMX and its composites, i.e. the less the E_N–N is, the larger the sensitivity is. Additionally, molecular interactions are inherently disclosed by using pair correlation function (PCF) to analyze the interfacial structure between (1 0 0)HMX crystal surface and F₂₃₁₁ molecular chain.     

A modified equation of state for Xe at high pressures by molecular dynamics simulation

The exact equation of state （EOS） for the fission gas Xe is necessary for the accurate prediction of the fission gas behavior in uranium dioxide nuclear fuel, However, the comparison with the experimental data indicates that the applicable pressure ranges of existing EOS for Xe published in the literature cannot cover the overpressure of the rim fission gas bubble at the typical UO2 fuel pellet rim structure. Based on the interatomic potential of Xe, the pressure-volume-temperature data are calculated by the molecular dynamics （MD） simulation. The results indicate that the data of MD simulation with Ross and McMahan＇s potential [M. Ross and A. K. McMahan 1980 Phys. Rev. B 21 1658] are in good agreement with the experimental data. A preferable EOS for Xe is proposed based on the MD simulation. The comparison with the MD simulation data shows that the proposed EOS can be applied at pressures up to 550 MPa and 3 GPa and temperatures 900 K and 1373 K respectively. The applicable pressure range of this EOS is wider than those of the other existing EOS for Xe published in the literature.     

Surface diffusion of Si,Ge and C adatoms on Si （001） substrate studied the molecular dynamics simulation

Depositions of Si, Ge and C atoms onto a preliminary Si (001) substrate at different temperatures are investigated by using the molecular dynamics method. The mechanism of atomic self-assembling occurring locally on the flat terraces between steps is suggested. Diffusion and arrangement patterns of adatoms at different temperatures are observed. At 900 K, the deposited atoms are more likely to form dimers in the perpendicular [110] direction due to the more favourable movement along the perpendicular [110] direction. C adatoms are more likely to break or reconstruct the dimers on the substrate surface and have larger diffusion distances than Ge and Si adatoms. Exchange between C adatoms and substrate atoms are obvious and the epitaxial thickness is small. Total potential energies of adatoms and substrate atoms involved in the simulation cell are computed. When a newly arrived adatom reaches the stable position, the potential energy of the system will decrease and the curves turns into a ladder-like shape. It is found that C adatoms can lead to more reduction of the system energy and the potential energy of the system will increase as temperature increases.     

低能Pt原子与Pt(111)表面相互作用的分子动力学模拟

利用分子动力学模拟方法详细研究了低能Pt原子与Pt(111)表面的相互作用所导致的表面吸附原子、溅射原子、表面空位的产生及分布规律,给出了表面吸附原子产额、溅射原子产额和表面空位产额随入射Pt原子能量的变化关系.模拟结果显示:溅射产额、表面吸附原子产额和表面空位产额随入射原子的能量的增加而增加,溅射原子、表面吸附原子的分布花样呈3度旋转对称性质;当入射粒子能量高于溅射阈值时,表面吸附原子主要是基体最表面原子的贡献,入射粒子直接成为表面吸附原子的概率很小.其主要原因是:当入射粒子能量高于溅射能量阈值时,入射 关键词： 分子动力学 低能粒子 表面原子产额 空位缺陷 溅射     

I50V变异对HIV-1蛋白酶抑制剂Amprenavir抗药机制的分子动力学研究

HIV-1蛋白酶PR(HIV-1 protease)的变异对抑制剂产生抗药性,严重消弱抗艾滋病的治疗效果.I50V变异是HIV-1蛋白酶残基变异中最重要的一个.采用分子动力学模拟和溶解相互作用能方法SIE(solvated interaction energy)研究I50V变异对抑制剂APV(amprenavir)抗药机制.分子动力学分析表明I50V变异诱导HIV-1蛋白酶整体柔性的增加,影响了抑制剂与蛋白酶的相互作用.结合自由能计算表明范德华作用的下降驱动了I50V变异对APV的抗药性.基于残基的能量分解证明V50/V50'与APV的相互作用相对于野生型的I50/I50'明显减弱,诱导了抗药性.本研究能为高效的缓解抗药性抑制剂的研发提供一定的理论指导.     

Density functional theory and molecular dynamics simulation study on corrosion inhibition performance of mild steel by mercapto-quinoline Schiff base corrosion inhibitor

Corrosion inhibition mechanism of two mercapto-quinoline Schiff bases, eg., 3-((phenylimino)methyl)quinoline-2-thiol (PMQ) and 3-((5-methylthiazol-2-ylimino)methyl) quinoline-2-thiol (MMQT) on mild steel surface is investigated by quantum chemical calculation and molecular dynamics simulation. Quantum chemical parameters such as E_HOMO, E_LUMO, energy gap (ΔE), dipolemoment (µ), electronegativity (χ), global hardness (η) and fraction of electron transfers from the inhibitor molecule to the metallic atom surface (ΔN) have been studied to investigate their relative corrosion inhibition performance. Parameters like local reactive sites of the present molecule have been analyzed through Fukui indices. Moreover, adsorption behavior of the inhibitor molecules on Fe (1 1 0) surface have been analyzed using molecular dynamics simulation. The binding strength of the concerned inhibitor molecules on mild steel surface follows the order MMQT>PMQ, which is in good agreement with the experimentally determined inhibition efficiencies. In view of the above, our approach will be helpful for quick prediction of a potential inhibitor from a lot of similar inhibitors and subsequently in their rational designed synthesis for corrosion inhibition application following a wet chemical synthetic route.     

气体凝聚团簇源中团簇形成的DSMC研究

利用直接模拟蒙特卡洛方法(DSMC) ,模拟了气体凝聚团簇源的引出口尺寸和中心位置不同的条件下,Cu团簇的尺寸分布以及模拟了随着时间的增长,腔内团簇数目的变化.模拟结果表明:引出口的直径越大,产生大团簇的比例越小;在引出口的直径相同的情况下,引出口的中心位置偏离坐标原点比在原点产生的大团簇的比例要大;随着时间的增长,腔内团簇数目先变多后变少.     

引出口的几何参数对团簇形成影响的DSMC研究

利用直接模拟蒙特卡洛方法(DSMC),模拟了气体凝聚团簇源的引出口尺寸和中心位置不同的条件下,Cu团簇的尺寸分布以及模拟了随着时间的增长,腔内团簇数目的变化.模拟结果表明:引出口的直径越大,产生大团簇的比例越小;在引出口的直径相同的情况下,引出口的中心位置偏离坐标原点比在原点产生的大团簇的比例要大;随着时间的增长,腔内团簇数目先变多后变少.     

冲击作用下黑索金（RDX）热分解动力学模拟

应用分子动力学模拟方法研究了黑索金(RDX)在冲击作用下的分解机理, 研究结果表明RDX初始分解机理主要为N-N键的断裂形成NO2分子, 然后发生比N-N键断裂更为强烈的C-N键断裂反应形成N2, CO和CO2分子; 在恒定温度(如300K)下,冲击速度增大对加快反应影响不大, 说明高温热点的形成对起爆的重要性.     

高温下黑索金（RDX）热分解动力学模拟

应用分子动力学模拟方法研究了黑索金(RDX)在纯高温下的分解机理, 研究结果表明RDX初始分解机理主要为N-N键的断裂形成NO2分子, 然后发生H原子转移反应形成H2O, HONO, HO和NO分子; 通过对RDX热分解反应物和生成物的研究结果表明N2和H2O分子是RDX分解过程中最稳定的生成物, NO2, HNO3, NO, NO3和HONO分子为RDX热分解过程中的中间产物; 在高温4500K, CO, CO2和OH分子出现的频率逐渐提高, 表明这几种分子在高温下更容易形成.     

冲击作用下黑索金(RDX)热分解动力学模拟

应用分子动力学模拟方法研究了黑索金(RDX)在冲击作用下的分解机理,研究结果表明RDX初始分解机理主要为N-N键的断裂形成NO2分子,然后发生比N-N键断裂更为强烈的C-N键断裂反应形成N2,CO和CO2分子;在恒定温度(如300K)下,冲击速度增大对加快反应影响不大,说明高温热点的形成对起爆的重要性.