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International audience; In a preliminary study [Phys. Chem. Chem. Phys., 2017, 19, 15247], we have recently documented an elusive mechanism underlying the cluster formation in model fluids with microscopic competing interactions (hard-sphere two-Yukawa). This mechanism consists in a tiny rearrangement of a distant correlation peak in the local density profile. For weak attractions, this peak contributes to the shallow, long-wave oscillation typical of such fluids; as the attraction strengthens, such a portion progressively disengages from the long-range behaviour, and moving backwards takes on the character of a new shell of neighbours, falling beyond the existing ones at shorter distances. This “reversal of trend” – despite its tiny size, in comparison with the overall aspect of the density profile – is shown to precisely occur at the onset of clustering. The scope of the present study is twofold. In the first instance, we positively assess our preliminary finding. To this aim we have studied by Monte Carlo simulations different families of two-Yukawa fluids, under the same conditions investigated in the original paper, namely fixed temperature, high fluid-density and increasingly attractive strength. Apparently, the reversal of trend in spatial correlations sets as a sensitive criterion to identify the clustering threshold, complementing other common indicators, based on the modifications undergone by the low-wavevector peak in the structure factor. Secondly, we document the accuracy of the Hypernetted Chain theory in predicting the spatial rearrangement under scrutiny. This evidence paves the way to an extended investigation of the observed phenomenology by the complementary use of theoretical and simulation tools.

When liquids are cooled below their melting temperature Tm, sometimes they do not solidify immediately but remain in supercooled state up to temperatures far below the melting point. Under certain conditions, they can solidify into the form of amorphous solids without crystallizing. A supercooled liquid and a amorphous solid are metastable phases, which are not completely understood in terms of structural arrangement and thermodynamic behaviour. But by far the most interesting feature is the glass transition which is the manifestation of a true thermodynamic transition and a dynamic event since a dramatic dynamic arrest intervenes. A unified theory of supercooled liquids and glass transition does not yet exist and, more specifically, the link between the sharp increase of the relaxation time and the correlation length is a question still largely open. This article presents in the most elementary manner a brief overview of this delicate issue.

International audience; We study the correlation and structural functions of symmetric amphiphilic systems. The systems are modelled by a double Kac potential and their structure is analyzed analytically in the random phase approximation (RPA) of the liquid state theory combined with the hard-sphere (HS) reference system. The microscopic approximation applied to the model yields a theory consistent with the phenomenological Landau-Ginzburg theory of microemulsions. When the amount of surfactant in the microemulsion is increasing, the behaviour of the total correlation function changes from an exponential decreasing to a damped oscillatory decaying, and the peak emerging in the structure factor of amphiphilic systems grows up in agreement with the small-angle neutron scattering experiments. The Lifshitz line – at which the peak in the structure factor is no longer at the zero wave vector – could be reached with specific values for the parameters characterizing the structure of the model.

International audience; This review seeks to describe, from first principles, the nature of the interaction forces in atomic and ionic liquids. The atoms and molecules made up of dipoles and multipoles interact with van der Waals forces, while the ionic systems are viewed as pseudoions interacting through effective forces depending on the electronic structure and the physical ionic arrangement. The interplay between these two aspects of materials is quite complex and forms the main subject of this review. As it will be shown, the two-component system of interacting electrons and ions can be reduced, in second order perturbation theory, to an effective one-component system made up of pseudoions acting under the influence of two-body, central, screened potentials. These potentials result from a weak interaction between the electrons and the ions, deduced from the pseudopotential theory. Once the interatomic forces are known, the atomic structure and the electronic transport properties can be determined by methods of classical mechanics and quantum mechanics. Besides, a large volume-dependent term in the free energy, independent of the ionic positions, which distinguishes the conducting liquids from the simple isolator liquids like argon, is indispensable for explaining the thermodynamical properties.

We study theoretically a prototype hard-sphere two-Yukawa model with competing interactions, under thermodynamic conditions associated with the formation of clusters. We adopt the analytically solvable random phase approximation and show that this theory predicts reasonably well the structure of the fluid—in comparison with exact Monte Carlo results—within a unique parameterization of the direct correlation function inside the hard core of particles. In particular, the theory follows correctly the development, in the structure factor, of a local peak at low wavevectors, as peculiarly associated with the onset of aggregation. We then model the direct correlation function in the same wavevector regime by a Gaussian function, so as to systematically investigate, in a “reverse” scheme, how varying the properties of the local peak modifies the original underlying competing interaction. We show that large variations in the height of the peak are generally associated with comparatively smaller variations in the height of the microscopic repulsive barrier; moreover, the shrinking and shifting towards lower wavevectors of the peak may be interpreted in terms of the displacement of the barrier, producing a substantial enlargement of the range of both the attractive and repulsive contributions to the interaction potential. Finally, we document the way the repulsive barrier tends to vanish as the two-Yukawa fluid approaches a “simple fluid” behavior, heralding the onset of a liquid-vapor phase separation.We study theoretically a prototype hard-sphere two-Yukawa model with competing interactions, under thermodynamic conditions associated with the formation of clusters. We adopt the analytically solvable random phase approximation and show that this theory predicts reasonably well the structure of the fluid—in comparison with exact Monte Carlo results—within a unique parameterization of the direct correlation function inside the hard core of particles. In particular, the theory follows correctly the development, in the structure factor, of a local peak at low wavevectors, as peculiarly associated with the onset of aggregation. We then model the direct correlation function in the same wavevector regime by a Gaussian function, so as to systematically investigate, in a “reverse” scheme, how varying the properties of the local peak modifies the original underlying competing interaction. We show that large variations in the height of the peak are generally associated with comparatively smaller variations in the ...

Two scaling laws are investigated, which are devoted to link the diffusion coefficient to the thermodynamic properties for the athermal hard-sphere system, over the wide range of packing fraction covering the stable and metastable regimes. It is found that the most relevant control parameter is not the excess entropy, but the compressibility factor, i.e. the logarithm derivative of the excess entropy with respect to the packing fraction.

We use Monte Carlo simulations to carry out a thorough analysis of structural correlations arising in a relatively dense fluid of rigid spherical particles with prototype competing interactions (short-range attractive and long-range repulsive two-Yukawa model). As the attraction strength increases, we show that the local density of the fluid displays a tiny reversal of trend within specific ranges of interparticle distances, whereupon it decreases first and increases afterwards, passing through a local minimum. Particles involved in this trend display, accordingly, distinct behaviours: for a sufficiently weak attraction, they seem to contribute to the long-wave oscillations typically heralding the formation of patterns in such fluids; for a stronger attraction, after the reversal of the local density has occurred, they form an outer shell of neighbours stabilizing the existing aggregation seeds. Following the increment of attraction, precisely in correspondence of the local density reversal, the local peak developed in the structure factor at small wavevectors markedly rises, signalling—in agreement with recent structural criteria—the onset of a clustered state. A detailed cluster analysis of microscopic configurations fully validates this picture.

A set of three different scaling laws is investigated, which are devoted to link the transport properties, i.e. diffusion coefficient, shear viscosity, bulk viscosity and thermal conductivity, to the thermodynamic properties for the athermal hard-sphere system, over the wider range of packing fraction covering the stable and metastable regimes. Except for the thermal conductivity, the Rosenfeld (1999) [15] relation is found to be applicable to the stable states while the Adam and Gibbs (1965) [24] relation holds well for the metastable states. In contrast, the modified Cohen and Turnbull (1959) [25] relation proposed here gives sound support for a universal scaling law connecting the dynamic and thermodynamic properties, over the domain of packing fraction including the stable and metastable states. In particular, it is found that the most relevant control parameter is not the excess entropy, but the logarithm derivative of the excess entropy with respect to the packing fraction. In the same context, the Stokes–Einstein relation between the diffusion coefficient and the shear viscosity is also examined. The possible violation of the Stokes–Einstein relation is investigated over a large domain of packing fractions.

The investigation of the thermodynamic properties of the Lennard–Jones (LJ) fluid is made by means of a system of particles interacting with a potential of hard-core plus attractive Yukawa tail (HCY). Due to the similarity between the LJ potential and the HCY potential in its overall form, it is worthwhile seeking to approximate the LJ potential in much the same way that the hard-sphere reference potential has been so used. The study consists in describing the thermodynamics of the LJ fluid in terms of the equivalent HCY system, whose the properties are known accurately, by means of mapping the thermodynamic quantities for the HCY potential parameters. The method is feasible owing to a convenient analytical expression of the Helmholtz free energy from the mean-spherical approximation expanded in power of the inverse temperature. Two different procedures are used to determine the parameters of the HCY potential as a function of the thermodynamic states: one is based on the simultaneous fits of pressure and internal energy of the LJ system and the other uses the concept of collision frequency. The reasonable homogeneity of the results in both procedures of mapping makes that the HCY potential is a very good reference system, whose the proposed theoretical expressions can be used confidently to predict the thermodynamic properties of more realistic potentials.

We report a study of structural and thermodynamic properties of liquid aluminium, thallium, and lead by molecular dynamics (MD) simulations as well as integral equation (IE) theory. As an input, we consider an effective pair potential constructed within the framework of the second-order pseudopotential perturbation theory using a model potential initially designed for the solid state. Comparing our MD results of thermodynamic melting temperature and static structure with experimental data, we show that the pseudopotential used is transferable to the liquid state near the melting point for Tl and Pb, and to a lesser extent for Al. From a theoretical point of view, we find that an IE method of the hypernetted-chain-type gives reasonable results for the structure factor and isothermal compressibility for these elements whose interactions have a marked ionic character.

We propose a novel approach to calculate the thermodynamic phase diagrams. Differing from the conventional method in which the boundaries of the coexisting phases are the ultimate goal, the present work crosshatches the domains of the homogeneous phase and also the phases in coexistence. This was done by treating the separated phases as a composite system whose Helmholtz free energy density is expressed as the sum average of the constituent free energy densities which are weighed by their respective volume proportions. As a result, both the domains of the coexisting phases and the homogeneous single phase can be determined in addition to locating the phase boundaries, customarily obtained by imposing the thermodynamic equilibrium conditions of equal pressure and equal chemical potential. We illustrate the elegance of the theory by studying a thermally responsive microgel system.

The thermophysical properties of expanded liquid mercury have been investigated along the liquid-vapor coexistence curve by using Monte Carlo and Molecular Dynamic simulations. For the purpose, an empirical state dependent interatomic potential for the region of dense metallic liquid is used, while the state dependence is not necessary near the critical point. In order to test the validity of this potential, we determine the surface layering and the sound velocity, two properties very sensitive to the choice of the potential. Our results are in quite good agreement with other theoretical results and to the experimental data available in the literature.

The standard integral equation approach is used to extract the bridge function and other correlation functions of hard spheres fluid. To achieve this, we first use a recent consistent closure relation proposed by Bomont et al. [J. Chem. Phys. 119, 2188 (2003)] that has already proven to be accurate to describe the Lennard-Jones fluid properties. Second, we take advantage of the coherent scheme derived by Bomont [J. Chem. Phys. 119, 11484 (2003)] to calculate the excess chemical potential, the entropy and some relative transport properties. Very good agreement is obtained for structural quantities and thermodynamic properties as compared to exact data at densities ranging from 0.1 to 0.9.

The integral equation theory is used to investigate the structural and thermodynamic properties of the Lennard-Jones fluid with a new approximate bridge function, which is based on the modification of its expansion in powers of the thermal potential. The thermodynamic consistency is achieved via the virial and compressibility routes. The problem of the renormalization of the indirect correlation function is also considered with an original prescription for partitioning the pair potential. The bridge function as well as the excess chemical potential and the excess entropy, which are calculated by means of standard formulas of statistical mechanics, are compared to simulation data. The thermodynamic properties of the supercritical Lennard-Jones fluid calculated with the present closure relation are in excellent agreement with those obtained from computer simulation.

Understanding the interatomic interactions in noble gases remains one of the fundamental problems not completely solved to date. From small-angle neutron scattering experiments it is well-known that three-body forces exist and cannot be neglected. On the theoretical side, semi-analytic and simulation methods have been used to reveal the nature of these many-body interactions. The purpose of the present work is to provide an overview of the different three-body contributions to the interactions and their relative importance in describing the structural and thermodynamic properties for noble gases by means of the integral equation theory and molecular dynamics simulations. We examine the relevance of the effective state-dependent pair potential in this framework, as well as the self-consistency problem that we are faced with in the integral equation theory.

A new approximate bridge function is proposed as an expansion in powers of the thermal potential, which ensures the thermodynamic consistency with the classical pressure-compressibility condition. The bridge function compares very well the simulation data at large separation as well as in the most important region of the core. The thermodynamic properties of the supercritical Lennard-Jones fluid calculated by means of standard formulas of statistical mechanics involving correlation functions and bridge function are in excellent agreement with those obtained from computer simulation.

An analysis of the entropy dependence of the diffusion coefficient is presented in terms of the positional correlations in a fluid of hard spheres, with the objective to investigate the scaling law relating the diffusion coefficient and the excess entropy proposed many years ago and established empirically by the simulations. It is found that the exponential behavior between the reduced diffusion coefficient and the excess entropy is observable over a restricted range of densities, where the hydrodynamic behavior of the hard-sphere fluid is readily describable by a nearly exponential velocity autocorrelation function as prescribed by the Enskog theory. From this analysis, a semiempirical expression for the diffusion coefficient of the dense fluids is proposed in terms of the pair correlation function.

The structural properties and the atomic dynamics of liquid and supercooled silicon are investigated by a molecular dynamics simulation, using the empirical Stillinger–Weber (SW) potential. The description of the structure factor is in good agreement with very recent X-ray diffraction experiments, provided that the SW model is modified by taking into account new experimental results of the density in the stable liquid near the melting point. The features of the velocity autocorrelation function and the corresponding spectral density are examined. The SW potential appears to be well-designed for studying disordered phases of silicon. In particular, it allows us to investigate the process giving rise to the supercooled states, which are associated to a gradual increase of the density as confirmed by recent experiments.

The dynamic correlations of Cs are investigated along the liquid–vapour coexistence curve in terms of the velocity autocorrelation function (VACF). First, the microscopic theory of liquid metals is used to generate the interionic pair potential, u(r), and then molecular dynamics (MD) are used to calculate the corresponding pair correlation function, g(r), the VACF, ψ(t), and the self-diffusion coefficient, D. In addition, the evolution of ψ(t) and D with density is predicted using a simple analytical model based on single-particle motion. The results are found to be in good agreement with our MD simulation data.

The diffusion of atoms in liquid Li, Na, K, Rb, and Cs is investigated near the melting point. The pair interactions are described with the pseudopotential of Fiolhais et al. [Phys. Rev. B 51 (1995) 14001; 53 (1996) 13193(E)] and the properties of the alkali elements are calculated by molecular dynamics simulation. The static structure, the velocity autocorrelation function, its spectral density, as well as its memory function are computed. It is found that the diffusion coefficients extracted from these functions are in good agreement with the experimental data. Besides, the existence of a scalable behaviour for these properties is discussed.

The standard integral equation approach is used to extract the bridge function and other correlation functions of simple fluids. To do this, we firstly use the hybridized mean spherical approximation (HMSA), which involves a renormalization of the indirect correlation function. Secondly, we propose a new division scheme for the pair potential founded on the merging process of a test particle into the system. Thirdly, we take advantage of the thermodynamic consistent condition put forward in the HMSA to optimize the depth of the long-range part of the pair potential inside the core, making the procedure autonomous and state dependent. The method is tested on the pure Lennard-Jones fluid in supercritical conditions. Very good agreement is obtained for structural quantities and thermodynamic properties as compared to the Monte Carlo (MC) results for the bridge function and to the molecular dynamics (MD) results for the thermodynamic properties.

A new division scheme for the pair potential into long-range and short-range parts is presented, which takes account of the dependence on the density and makes possible the extraction of the bridge function B(r) in the core region. The calculation of the correlation functions is carried out with the hybridized mean spherical approximation (HMSA). As attested by the comparison with the simulation results, HMSA used with this potential separation is suitable to produce accurate bridge function and pair correlation function for the Lennard-Jones fluid.

Molecular dynamics simulations are used to study the static structure, the thermodynamics, and the dynamic correlations in liquid alkaline-earth metals from beryllium to barium near the melting point. The properties like structure factor, binding energy, specific heat at constant volume, velocity autocorrelation function, its spectral density, and self-diffusion coefficient are calculated with a pair potential obtained from a pseudopotential originally developed for the solid state. Good agreement with the experiment is observed for the stucture factor and the binding energy, and the computed velocity autocorrelation functions compare favorably with the results obtained by other theoretical calculations, showing the transferability of the pseudopotential used from solid to liquid environment in the case of alkaline-earth metals.

The self-consistent integral equation method is applied to calculate the structure and the thermodynamic properties of supercritical argon considered in a recent neutron-scattering experiment by Pfleiderer et al. [J. Chem. Phys. 111, 2641 (1999)]. Two kinds of potentials, different in nature, are used for the calculations. One is an empirical standard potential and the other is founded upon ab initio quantum chemical calculations. The small discrepancies between the two approaches are discussed, and the results are compared to the recent measurements for structure and experimental thermodynamic properties as well.

The asymptotic dependence of the local-field correction function, G ( q ), is investigated in determining the structure of simple liquid metals. We compare two variants of G ( q ), the well-known one of Ichimaru and Utsumi, and the more recent one proposed by Farid and co-workers. As the wavevector q tends to zero, both functions coincide exactly, while as q tends to infinity the former has a horizontal asymptote and the latter has a parabolic dependence. After computing the pair potential, u ( r ), for Na and Al with both local-field functions, we deduce the structure factor, S ( q ), and the pair distribution function, g ( r ), in the framework of the soft-core mean spherical approximation. It is shown that u ( r ), g ( r ), and S ( q ) are very sensitive to the low- q ( q k F ) behaviour of G ( q ), but quite not to its large- q one.

The static and dynamic structure factors of liquid lithium near the melting point are calculated with the electron–ion potential of Fiolhais and co-workers, which was originally developed for the solid state. After computing the effective pair potential u ( r ), we deduce the structure factor and the pair correlation function in the framework of the soft-core mean spherical approximation. Then, we calculate the dynamic structure factor S ( q , ω ) within the viscoelastic model. The influence of the local-field correction is discussed by comparing the results with experimental measurements and the transferability of the model potential from solid to liquid environment is shown.

The formalism of the hybridized mean spherical approximation integral equation is extended to calculate the pair correlation function for krypton, beyond the critical isotherm, by using the two- and three-body contributions to the interatomic potential. The calculations are intended to examine the change of the pair correlation function caused by the inclusion of the Axilrod-Teller triple-dipole potential. It is seen that the three-body interaction cannot be ignored and that their effects become more significant for intermediate densities. In addition, a good agreement is found with the recent small-angle neutron-scattering experiments of Formisano et al. [Phys. Rev. Lett. 79, 221 (1997)].

The structural and thermodynamic properties of liquid alkali metals near the melting point are presented. For this purpose, we use the thermodynamically self-consistent integral equation of the liquid state theory, called the hybridized mean-spherical approximation (HMSA). The effective interionic potential is derived via the second-order pseudopotential-perturbation method, in which the very recent pseudopotential of Fiolhais et al. [Phys. Rev. B 51, 14001 (1995)], designed for the solid state, is combined with our semianalytical local-field function [J. L. Bretonnet and M. Boulahbak, Phys. Rev. B 53, 6859 (1996)]. We show that this pseudopotential is transferable to the disordered environment characteristic of the liquid state and, if used with our local-field function, predicts the structural and thermodynamic properties of the liquid alkali metals with a reasonable accuracy.

A new modified hypernetted-chain integral equation for simple fluids is proposed in order to extract the bridge function by means of an iterative and self-consistent process based on the renormalization of the indirect correlation function. We have tested the method for pure Lennard-Jones potential, and our results are compared to those obtained with classical parametrized bridge functions as well as Monte Carlo simulation. It is a matter of fact that the role of the renormalization of the indirect correlation function is to improve the behavior of the bridge function all over the range of distances. Many states near the triple point and under supercritical conditions have been investigated: at high densities, very good agreement is found for structural quantities and thermodynamic properties as compared to other accurate constructions, whereas at low densities our results reduce to those of the standard integral equations.

The ionic and electron - ion structures of liquid Ga are investigated. The ionic pair potential is calculated using Shaw's optimized model potential and three different local-field corrections: Vashishta and Singwi's, Ichimaru and Utsumi's, and the very recent Ortiz and Ballone one. This latter, unlike both of the others, gives pair potentials that predict very well the experimental structure factor of liquid Ga. Investigation of the electron - ion structure factor and the pair distribution function shows an anomalous behaviour that is discussed.

The liquid structure and thermodynamics of the 3d-transition metals are calculated self-consistently via the hybridized mean spherical approximation (HMSA) integral equation. A local form factor, including the s-d mixing through an inverse scattering approach, is used to deduce effective pair potentials suitable for transition metals. The internal energy, which follows from the second-order pseudopotential perturbation method, contains in addition a d-band contribution expressed by the Friedel rectangular model for the density of d-states. It is found that the pair-correlation functions calculated with the HMSA and the molecular dynamics agree quite well with experiment except for the elements at the beginning of the 3d-series. The resulting thermodynamic quantities, necessary to achieve thermodynamic self-consistency, compare reason- ably well to our previous calculations using the Gibbs-Bogoliubov variational scheme.

This chapter is an introduction to the thermodynamics of systems, based on the correlation function formalism, which has been established to determine the thermodynamic properties of simple liquids. The article begins with a preamble describing few general aspects of the liquid state, among others the connection between the phase diagram and the pair potential u(r), on one hand, and between the structure and the pair correlation function g(r), on the other hand. The pair correlation function is of major importance in the theory of liquids at equilibrium, because it is required for performing the calculation of the thermodynamic properties of systems modeled by a given pair potential. Then, the article is devoted to the expressions useful for calculating the thermodynamic properties of liquids, in relation with the most relevant features of the potential, and provides a presentation of the perturbation theory developed in the four last decades. The thermodynamic perturbation theory is founded on a judicious separation of the pair potential into two parts. Specifically, one of the greatest successes of the microscopic theory has been the recognition of the quite distinct roles played by the repulsive and attractive parts of the pair potential in predicting many properties of liquids. Much attention has been paid to the hard-sphere potential, which has proved very efficient as natural reference system because it describes fairly well the local order in liquids. As an example, the Yukawa attractive potential is also mentioned.

We investigate the temperature threshold whereupon two-Yukawa systems with microscopic competing interactions transform from normal fluids to ‘cluster fluids’. Specifically, we apply two refined, thermodynamically self-consistent integral equation theories of the liquid state to study a family of two-Yukawa models having the same interaction strength, independent of the choice of potential parameters. We find, over the range of potential parameters and fluid densities investigated, an almost linear scaling between the temperature threshold for the cluster formation and the height of repulsive interactions, with higher barriers stabilizing the cluster fluid at higher temperatures. Cluster–cluster correlation lengths seem instead to be influenced by the long-range features of the interactions.

The structure factors of liquid Rb and Cs are calculated along the liquid-vapour coexistence curve from the triple point to the critical point. The calculations are performed within the soft-core mean spherical approximation and using an effective pair potential derived from pseudopotential theory. The results are in reasonable agreement with experiments. In particular, they give useful information about the limitation of the pseudopotential theory when the metal-non-metal transition is approached.

The results of calculations of the static structure factors, S(q), for liquid 3d transition metals are presented. These have been studied using effective interionic pair potentials derived from a local approach that combines the empty-core model to describe the nearly free electron sp band with a d-band contribution deduced from an inverse scattering method. The liquid structure is calculated using the variational hypernetted chain theory. The resulting S(q)s agree reasonably well with the experimental X-ray diffraction data.

An accurate thermodynamically self-consistent integral equation theory of the liquid state is used to investigate model fluids with competing attractive interaction at short distances and long-range repulsion, focusing on thermodynamic states where the formation of clusters is expected to occur. We find a remarkable accuracy of theoretical predictions, through a detailed assessment against results of Monte Carlo simulations. The behavior of theoretical radial distribution functions and structure factors faithfully follows the onset and growth of cluster aggregates in the homogeneous dense-vapor phase. The thermodynamic properties of the system sensitively depend on the ratio between the repulsive barrier and the attraction strength. We elucidate the role of accurate theoretical tools to investigate the properties of fluids with complex phase behaviors.

Oscillatory density profiles are a well-known feature occurring at the free surfaces of liquid metals. Recently, the thermophysical properties of expanded liquid mercury have been successfully investigated with an atypic isotropic effective interaction Bomont et al., J. Chem. Phys. 124, 054504 2006 . We use this model to investigate the liquid-vapor interface properties taking explicitly into account the density dependence of the potential related to the metal-nonmetal transition along the interface. Ionic and electronic density distributions along the normal of the interface display strong stratification and the calculated reflectivities compare well with experimental data.

The electrical resistivity ϱ and the thermoelectric power S have been measured for the liquid AlCu alloys, from the liquidus to 1300°C, in the whole phase diagram. The resistivity isotherms show one maximum at about 25 at. % Al, which is correctly interpreted by the t-matrix formalism, in the framework of the Faber-Ziman theory. The thermopower decreases abruptly in the range of 20 – 40 at. % Al, when Al is added, but this variation cannot be explained by the nearly free electron model.

New properties for the one particle bridge function B(1)(r), which are necessary to the calculation of the excess chemical potential betamue), are derived for the hard sphere fluid. The method, which only requires the knowledge of the bridge function B(2)(r), is based on an investigation of the correlation function dependence on the Kirkwood charging parameter. In this framework, the unavoidable question of topological homotopy is addressed. As far as B(2)(r) is considered as exact, this work provides useful information on B(1)(r) in the well identified dynamical regimes of the hard sphere fluid. Signatures of the transitions between these regimes are identified on the trends of B(1)(r). This approach provides self-consistent results for betamue) that agree very well with simulation data.

We report a Brownian isothermal molecular dynamics simulation study of bimetallic clusters. Beginning at their lowest energy structures which were obtained from a recently developed algorithm [P. J. Hsu and S. K. Lai, J. Chem. Phys. 124, 044711 (2006)], we investigate the effect of temperature on the thermal and geometric of ${\mathrm{Cu}}_{m}{\mathrm{Au}}_{n\ensuremath{-}m}$ at given nuclearity $n$. We study in particular the change in temperature of the relative root-mean-squared bond length fluctuation $\ensuremath{\delta}$ so-called Lindemann parameter and exploit the underlying mechanism that leads to its thermal variation. We then discuss the correlation of $\ensuremath{\delta}$ to the specific heat which is used generally to deduce the bulklike melting of bimetallic clusters. The mismatch quite often seen at the melting temperature between $\ensuremath{\delta}$ and specific heat can now be understood better.

Les metaux, qui sont d'excellents conducteurs d'electricite et de chaleur, occupent une place speciale dans l'etude des etats de la matiere. D'ailleurs, s'il fallait definir un corps metallique au moyen d'une propriete unique, la meilleure serait incontestablement son coefficient thermique de resistivite. En effet, l'etat metallique est caracterise par une resistance electrique faible qui augmente avec la temperature et qui double sensiblement a la fusion. L'etude, tant experimentale que theorique, des proprietes de transport electronique des metaux et alliages a l'etat liquide a subi un regain d'interet, dans les annees soixante, grâce aux travaux de Ziman et de ses collaborateurs [1]. Ces auteurs ont developpe une theorie de la resistivite et du pouvoir thermoelectrique, resultant de la conjugaison de la theorie electronique des metaux et de la theorie des fluides classiques. Neanmoins, pour une etude elementaire de la resistivite, on peut utiliser la theorie classique des electrons libres, elaboree par Drude au debut du siecle. Dans celle-ci on neglige les actions reciproques des ions avec les electrons de conduction et l'on admet que ces derniers sont entierement libres de se mouvoir au sein de l'echantillon. Le principal succes de cette theorie a ete la justification de la relation de Wiedemann et Franz entre les conductivites electrique et thermique, qui avait ete etablie experimentalement quelque temps auparavant. Cependant, meme dans le cas des metaux qui se rapprochent le plus du modele des electrons libres, tels que le sodium, le cuivre et l'argent, il n'est pas correct de negliger l'influence de l'attraction electrostatique des ions sur la distribution des charges electroniques, c'est pourquoi, en depit de ses succes, la theorie de Drude a rencontre de serieuses difficultes. Les plus importantes concernaient la chaleur massique, beaucoup plus elevee qu'elle ne l'est en realite, et la loi de variation de la resistivite avec la temperature en T 1/2 , qui varie, en fait, proportionnellement a la temperature. Cet article presente une selection des resultats experimentaux de la resistivite des metaux fondus. Neanmoins, une place est reservee a l'expose succinct de la theorie de la conduction dans les metaux ainsi qu'a la description des principales techniques de mesure de la resistivite des metaux liquides.

Molecular-dynamics simulation is used to compute the pair correlation function and the velocity autocorrelation function of Cs and Rb along the liquid-vapor coexistence curve, from which the excess entropy S(ex) and the diffusion coefficient D are deduced. The numerical results of both physical properties are correlated and a scaling law between the excess entropy and the reduced diffusion coefficient D(*)(=D/D(0)) is investigated for different expressions of the reduction parameter D(0). The choice of thermodynamic states along the liquid--vapor coexistence curve gives us the possibility to extend the investigation of the relation between the reduced diffusion coefficient and the excess entropy over a wide area and to test the adequacy of the scaling law confidently.