分子动力学模拟研究[Bmim][PF6]+水+醇三元体系的微观结构和分子间相互作用

研究离子液体体系的微观结构和分子间相互作用具有重要意义. 本文对1-丁基-3-甲基咪唑六氟磷酸盐([Bmim][PF₆])+水+乙醇和[Bmim][PF₆]+水+异丙醇三元体系进行了分子模拟研究, 计算了径向分布函数和不同组成的水-醇混合溶剂与离子液体阴阳离子间的相互作用能, 并将其分解为库仑相互作用能和Lennard-Jones(LJ)势能. 在此基础上, 研究了溶液体系的微观结构、分子间相互作用和相行为. 结果表明, 水倾向于与离子液体阴离子和阳离子极性部分作用, 醇倾向于与阴离子和阳离子非极性部分作用; 库仑力主导阴离子-溶剂相互作用, 色散力主导阳离子-溶剂相互作用, 阴阳离子的缔合状态对色散力影响较小, 对库仑力的影响非常显著.     

Transport Coefficients in Some Stochastic Models of the Revised Enskog Equation

A stochastic model of the revised Enskog equation is considered. A choice of the smearing function suggested by the work of Leegwater is used to apply the model to the repulsive part of the Lennard-Jones potential and the inverse-power soft-sphere potential. The virial coefficients obtained from the equilibrium properties of the models are in excellent agreement with the known exact coefficients for these models. The transport coefficients for the repulsive Lennard-Jones (RLP) model are also computed and appear to be of comparable accuracy to the Enskog-theory coefficients applied directly to a hard-sphere system, although exact results for the RLP with which to make an extensive comparison are not yet available. The pressure and the transport coefficients obtained from the model (shear viscosity, thermal conductivity, and self-diffusion) are compared with the pressure and the corresponding transport coefficients predicted by the Enskog and square-well kinetic theories.     

Elastic Scattering of Ultracold ^133Cs and SSRb Atoms in Triplet State

Elastic scattering properties of the ultracold interaction for the triplet state of ^133Cs and ^85Rb atoms are studied using two kinds of potentials by the same phase Ф. One is the interpolation potential, and another is Lennard-Jones potential （LJl2,6 ）. The radial Schrodtinger equation is also solved using two computational methods, the semiclassical method （WKB）, and the Numerov method. Our results are found to be in an excellent agreement with the more recent theoretical values. It shows that the two potentials and methods are applicable for studying ultracold collisions between the mixing alkali atoms.     

Heavy-ion fusion cross-section calculations in classical microscopic equations of motion approach

Fusion cross-sections for¹⁶O +¹⁶O reaction earlier calculated in classical microscopic equations of motion approach, with Lennard-Jones form ofNN interaction potential are overestimated compared to the experimental data at lower energies. This large deviation was attributed to possible break down of classical approximations at lower energies. The aim of this paper is to show that this discrepancy was rather due to certain assumptions made in the specification of initial conditions; in particular due to neglect of Coulomb interaction between the colliding ions at far off distances. Use of Lennard-Jones potential is also critically examined.     

Influence of DC electric field on the Lennard-Jones potential and phonon vibrations of carbon nanotube on catalyst

Influence of DC electric field on carbon nanotube (CNT) growth in chemical vapor deposition is studied. Investigation of electric field effect in van der Waals interaction shows that increase in DC electric field raises the magnitude of attractive term of the Lennard-Jones potential. By using a theoretical model based on phonon vibrations of CNT on catalyst, it is shown that there is an optimum field for growth. Also it is observed that CNT under optimum electric field is longer than CNT in the absence of field. Finally, the relation between optimum DC electric field and type of catalyst is investigated and for some intervals of electric field, the best catalyst is introduced, which is very useful for experimental researches.     

基于改进粒子群优化算法的氩原子团簇结构优化

采用改进粒子群优化算法(IPSO)结合Lennard-Jones势对氩原子团簇结构进行优化,得到了氩原子团簇的稳态结构能量。以氩原子团簇Arn（n = 2-14）为例,验证了该方法的有效性。结果表明,应用本文提出的方法可得到对称性良好的团簇结构。与基本粒子群优化算法(BPSO)及遗传算法(GA)相比,改进粒子群优化算法具有更好的收敛特性,能较快地得到氩原子团簇结构的最优解。     

Efficient Algorithms for Large Scale Global Optimization: Lennard-Jones Clusters

A stochastic global optimization method is applied to the challenging problem of finding the minimum energy conformation of a cluster of identical atoms interacting through the Lennard-Jones potential. The method proposed incorporates within an already existing and quite successful method, monotonic basin hopping, a two-phase local search procedure which is capable of significantly enlarging the basin of attraction of the global optimum. The experiments reported confirm the considerable advantages of this approach, in particular for all those cases which are considered in the literature as the most challenging ones, namely 75, 98, 102 atoms. While being capable of discovering all putative global optima in the range considered, the method proposed improves by more than two orders of magnitude the speed and the percentage of success in finding the global optima of clusters of 75, 98, 102 atoms.     

Orientations of special water dipoles that accelerate water molecules exiting from carbon nanotube

One-dimensional ordered water molecules entering and exiting from a carbon nanotube with an appropriate radius are studied with molecular dynamics simulations.It can be found that a water molecule near the nanotube end is more likely to be expelled from the nanotube if its dipole is almost perpendicular to the nanotube axis.The key to this observation is that those water molecules axe closer to the wall of the nanotube away from the equilibrium position of the Lennar-Jones (LJ) potential.Thus,the interaction energy for those water molecules is relatively high.There are two particular structures of the perpendicular water molecule depending on the dipole direction of the adjacent water molecule in the nanotube.Although the probabilities of these structures are quite small,their contributions to the net flux across the nanotube end are approximately equal to the predominant structures.The present findings further show the possibility of controlling the water flow by regulating the dipole directions of the water molecules inside the nanochannels.     

Ar＋TlF体系的转动非弹性散射

本文用一种新的方法求解A+BC体系的转动非弹性散射问题,即在径向耦合方程的势能耦合项中只取对角项,并用Morse势拟合Lennard-Jones势,从而可得去耦合径向方程的两个解集。渐近分析表明,此两个解集分别相应于入射波和出射波。将总波函数按总角动量的本征函数展开,展开系数为常数乘以上述得到的径向函数。再将总波函数代入Schrdinger方程,则可得到散射矩阵。计算结果表明,本法比IOS法更接近CC法,但计算量比后者少得多,且方法严谨。