Orientational correlations in molecular liquids by neutron scattering Carbon tetrachloride and germanium tetrabromide

Neutron diffraction structure factors for liquid carbon tetrachloride and germanium tetrabromide have been measured and are analysed to determine the molecular centre positional correlation function allowing for molecular angular correlation. The analysis shows quite unequivocally that appreciable molecular orientational correlations must exist in these liquids but that it may only extend to nearest neighbours. This is thought to cause the pair distribution function for the molecular liquids to be markedly different from that for atomic liquids such as argon and the difference is discussed.     

Comportement asymptotique de la fonction de distribution radiale dans les liquides

We study the influence of pair potential on the asymptotic behaviour of the radial distribution function in liquids. We use a perturbation expansion from a model of rigid spherical core inKirkwood's integral equation. It is pointed out that in metals as well as in insulators the asymptotic behavior is connected to that of the pair potential. However, the results are numerically different from those obtained from thePercus-Yevick approximation.     

A theory of electric polarisation in liquids : I. Nonpolar liquids

The static dielectric constant of nonpolar liquids is described by analyzing the pair distribution function and the dipole-dipole interaction into a finite set of Fourier components. In a mean field approximation the theory leads to a final formula that does not contain any adjustable parameter, and proves to work better than the Clausius-Mossotti equation. The theory explains in a satisfactory way the temperature and pressure dependence of the dielectric constant of nonpolar liquids, as well as the temperature variation of the refractive index of many organic polar liquids.     

Partial pair correlation functions and viscosity of liquid Al–Si hypoeutectic alloys via high-energy X-ray diffraction experiments

The liquid structure of Al–Si hypoeutectic binary alloys was characterized by diffraction experiments using a high-energy X-ray (synchrotron) beam source. The diffraction experiments were carried out for liquid pure Al, Al–3?wt% Si, Al–7?wt% Si, Al–10?wt% Si and Al–12.5?wt% Si alloys at several temperatures. The salient structure information such as structure factor (SF), pair distribution function (PDF), radial distribution function (RDF), coordination number (CN) and atomic packing densities (PD) were quantified as a function of Si concentration and melt temperatures. Reverse Monte Carlo (RMC) analysis was carried out using the diffraction experimental data to quantify the partial pair correlation functions, such as partial structure factor, partial pair distribution function (PPDF) and partial radial distribution function. Furthermore, the partial pair distribution function and the liquid atomic structure information were used in a semi-empirical model to evaluate the viscosity of these liquid alloys at various melt temperatures. The results show that the viscosity determined by semi-empirical methods using the atomic structure information is in good agreement with the experimentally determined viscosity values.     

Hurst's empirical law in the probability of atomic distribution in liquids

The rescaled range analysis was used to examine the pair distribution function of liquids. The global statistical dependence existed in the distribution of atoms in liquids. The probability of finding a particle at a distance r from a reference particle was subject to fractional Brownian motion. More importantly, the tendency of the Hurst exponent was away from the high rate when the change of liquid structure took place. This phenomenon showed that the liquid structural change was attributed to the variation of atomic distribution and the jump of the Hurst exponent was the indicator of the change from one phase to another in liquids.     

Is there icosahedral ordering in liquid and undercooled metals?

The local structure of simple liquids is significantly different from that of corresponding crystalline systems. Signatures of fivefold local ordering have been previously found, but current knowledge is limited to pair distribution, leaving considerable uncertainty in the determination of the geometrical structure. New x-ray absorption experimental results on liquid and undercooled liquid copper, interpreted using an advanced data-analysis method based on multiple-scattering simulations, are shown to contain direct information on triplet correlations making feasible a reliable determination of the bond-angle distribution and fraction of nearly icosahedral configurations in liquids.     

Proton Transport in Hydrogen-Bonded Chains in the Presence of an External Field

The motion of a kink pair consisting of kink soliton in different sublattices in hydrogen-bonded chains in the presence of an external force and damping is discussed based on a new soliton model. The scattering cross-section of a kink pair for an electromagnetic wave and the mobility of a kink pair are found.     

Partial chlorine-chlorine intermolecular scattering functions for XCl4 liquids (X = C,Si, Ge,V, Ti,Sn) from neutron diffraction and the RISM

Combining neutron diffraction intermolecular scattering functions with RISM partial scattering function for X-X and X-Cl atom paris the Cl-Cl partial scattering functions are obtained. The systematic trends in Cl-Cl partial scattering functions and radial distribution functions in six different tetrachloride liquids have been investigated. The intermolecular nearest neighbour Cl-Cl distance of 0·377(14) nm corresponds well with the value of 0·34 nm adopted for the chlorine hard sphere diameter in the RISM calculations.     

Shear induced anisotropy in two-dimensional liquids

The behavior of a dense two-dimensional soft disc liquid under shear is studied via nonequilibrium molecular dynamics. The structure factor for the liquid at a given shear rate is evaluated directly by plotting the particle positions, taken at random from the NEMD simulation at that shear, onto photographic film and using light scattering to obtain a diffraction pattern. The pair correlation function of this system is also extracted directly by histogramming the particle positions with respect to a given central particle as a function of separation and angle. The pair correlation function is compared to that approximated by a Fourier series expansion to rank ten. Results are reported as a function of shear rate from a shear rate of 0.1 (when the fluid is essentially Newtonian) to 10 (when the fluid can display a string phase). The appearance of the string phase is discussed and shown to be a consequence of the definition of temperature in the simulation algorithm. A modification of the algorithm is proposed. Comparisons between this work and previous work with three-dimensional liquids are given. The two-dimensional structure factor is compared with that obtained from a real colloidal suspension via light scattering.     

Dynamic structural correlations and Van Hove's correlation function for liquids

The stochastic model for liquids, developed previously and applied to the evaluation of static correlations, is extended to the evaluation of the dynamic pair correlation function. This extension can be achieved by a generalization of the width function W, characterizing the spread in the distribution of correlated local structures, from a piecewise linear function of r to a piecewise linear function in the (r, t) plane.     

Metallic liquids and glasses: atomic order and global packing

In this Letter, we have revealed the common structural behavior of metallic glasses through scrutinizing the evolution of pair distribution functions from metallic liquids to glasses and statistically analyzing pair distribution functions of 64 metallic glasses. It is found that the complex atomic configuration in metallic glasses can be interpreted globally as a combination of the spherical-periodic order and local translational symmetry. The implications of our study suggest that the glass transition could be visualized mainly as a process involving in local translational symmetry increased from the liquid to glassy states.     

Structure correlations of water molecules in a concentrated aqueous solution of ethanol

Monte Carlo calculation results for water–ethanol mixtures calculated in the isothermal and isobaric ensemble at T=300 K are presented. The analysis of the radial distribution functions for hydrogen bonding between ethanol molecule and water molecules was done. The concentrations of ethanol 0.75 show characteristics features of hydrogen-bonded liquids. The influence of the polar solvent molecule on water local structure and the hydrogen bond nets ware analyzed. Radial distribution functions for water–water interactions calculated in pure water and water–ethanol system are compared.     

Ultrasound scattering and the study of vortex correlations in disordered flows

In an idealized way, some turbulent flows can be pictured by assemblies of many vortices characterized by a set of particle distribution functions. Ultrasound provides a useful, nonintrusive, tool to study the spatial structure of vorticity in flows. This is analogous to the use of elastic neutron scattering to determine liquid structure. We express the dispersion relation, as well as the scattering cross section, of sound waves propagating in a "liquid" of identical vortices as a function of vortex pair correlation functions. In two dimensions, formal analogies with ionic liquids are pointed out.     

Diagrammatic analysis of correlations in polymer fluids: Cluster diagrams via Edwards’ field theory

Edwards’ functional integral approach to the statistical mechanics of polymer liquids is amenable to a diagrammatic analysis in which free energies and correlation functions are expanded as infinite sums of Feynman diagrams. This analysis is shown to lead naturally to a perturbative cluster expansion that is closely related to the Mayer cluster expansion developed for molecular liquids by Chandler and co-workers. Expansion of the functional integral representation of the grand-canonical partition function yields a perturbation theory in which all quantities of interest are expressed as functionals of a monomer-monomer pair potential, as functionals of intramolecular correlation functions of non-interacting molecules, and as functions of molecular activities. In different variants of the theory, the pair potential may be either a bare or a screened potential. A series of topological reductions yields a renormalized diagrammatic expansion in which collective correlation functions are instead expressed diagrammatically as functionals of the true single-molecule correlation functions in the interacting fluid, and as functions of molecular number density. Similar renormalized expansions are also obtained for a collective Ornstein-Zernicke direct correlation function, and for intramolecular correlation functions. A concise discussion is given of the corresponding Mayer cluster expansion, and of the relationship between the Mayer and perturbative cluster expansions for liquids of flexible molecules. The application of the perturbative cluster expansion to coarse-grained models of dense multi-component polymer liquids is discussed, and a justification is given for the use of a loop expansion. As an example, the formalism is used to derive a new expression for the wave-number dependent direct correlation function and recover known expressions for the intramolecular two-point correlation function to first-order in a renormalized loop expansion for coarse-grained models of binary homopolymer blends and diblock copolymer melts.     

Nuclear-magnetic-resonance measurements reveal the origin of the Debye process in monohydroxy alcohols

Monohydroxy alcohols show a structural relaxation and at longer time scales a Debye-type dielectric peak. From spin-lattice relaxation experiments using different nuclear probes, an intermediate, slower-than-structural dynamics is identified for n-butanol. Based on these findings and on translational diffusion measurements, a model of self-restructuring, transient chains is proposed. The model is demonstrated to explain consistently the so-far puzzling observations made for this class of hydrogen-bonded glass forming liquids.     

流体静态和动态平衡性质的分子动力学模拟

基于LJ势能模型和soft-sphere势能模型对不同状态下氩流体的径向分布函数、速度相关函数、横向粒子流相 关函数和中间散射函数进行模拟,重点讨论了LJ势能分子间吸引力和软心势能“软度”对流体静态和动态平衡性质的影 响,结果发现软心势能的影响比分子间吸引力的影响更显著,而且动态平衡性质中出现的振荡现象也是由软心势能所致。     

Cu-Ni合金结构的分子动力学模拟

采用EAM作用势对Cu Ni合金的结构特性进行了MD模拟研究 .通过FZ结构因子可发现 ,Cu含量的变化对结构因子的波动影响很小 ,键取向序参数和键对也表现出相似的变化规律 ,这表明液态Cu Ni合金对成份变化不敏感 ,体系中的化学序较弱 .将Cu70 Ni3 0 合金熔体的FZ结构因子与Waseda的实验结果进行对比 ,发现二者吻合得较好 ,表明EAM势可以很好地描绘Cu Ni合金的结构特性 .在快速冷却过程中 ,除了Cu2 0 Ni80 合金外 ,其他合金成份的双体分布函数的第二峰都发生了劈裂 ,标志着体系最终形成了非晶结构 ,而Cu2 0 Ni80 合金的双体分布函数却表现出晶体峰的特征 .通过对键取向序参数、键型指数以及铜镍原子的有效扩散系数的分析表明 ,在快速冷却过程中 ,Cu2 0 Ni80 合金最终形成了hcp晶体结构