Table of contents

An algorithm for the simulation of quantum–classical dynamics is presented. Quantum–classical evolution is effected by a propagator exp (i t) involving the quantum classical Liouville operator that describes the evolution of a quantum subsystem coupled to a classical bath. Such a mixed description provides a means to study the dynamics of complex many-body systems where certain degrees of freedom are treated quantum mechanically. The algorithm is constructed by decomposing the time interval t into small segments of length Δt and successively applying the propagator in the short time segments to obtain the evolution for long times. The algorithm is shown to be a discretization of the iterated Dyson form of the propagator whose direct solution is vexatious. The sequential short-time propagation algorithm is applied to the spin-boson model for a range of values of the Kondo parameter and shown to be effective.

We report an application of the general formalism of density functional theory (DFT) for quantum fluids at finite temperature to the case of helium. Using this approach, we compute the liquid-vapour coexistence curve and the surface tension of helium at low temperatures. We observe that the range of the interface is much larger than the usual 10-90 surface thickness, and we find that the DFT reproduces the T^7/3 temperature dependence of the surface tension. This implies that capillary-wave effects are, at least partially, accounted for by the density functional.

In this paper we shall discuss the viscosity of hydrogen as a prototype of a molecular fluid subjected to dissociation and ionization. In the dissociated phase we shall show that the dependence of the viscosity on temperature exhibits a crossover between an atomic and a screened plasma behaviour, as revealed by recent ab initio simulations. If this transition between molecular, atomic and plasma phase is well identified at low density (0.3 g cm⁻³), at higher density (0.75 g cm⁻³) the transition is more abrupt and no atomic phase can be identified.

In quantum solids composed of fermion particles, such as helium-3 and electrons, the low-temperature physics is governed by spin exchanges, according to the Thouless theory. We present path integral Monte Carlo calculations of ring exchange energies on 'clean' two-dimensional crystals of both helium-3 and electrons. We see a remarkable similarity of the results for these two 'opposite' systems. They are both ferromagnetic in the semi-classical limit (strong coupling) and antiferromagnetic near the melting transition where the relative exchange energies become equivalent. We focus here on the importance of long-ring exchanges near the melting transition. The total energy associated to exchanges may diverge, leading to a possible mechanism for the melting transition.

A density functional theory (DFT) for a two-component system of classical ions and degenerate electrons is presented. The theory is based on an 'orbital-free' free energy of the ion–electron plasma, which includes a square-gradient correction to the Thomas–Fermi kinetic energy of the degenerate electrons. Pair correlations in the metallic phase of hydrogen are calculated and compared to 'ab initio' DFT-MD simulation data. The freezing transition of a pressure-ionized hydrogen plasma and the plasma–insulator transition of spin-polarized fluid hydrogen are considered.

After a brief review of previous work, two exactly solvable two-dimensional models of a finite Coulomb fluid in a disc are studied. The charge correlation function near the boundary circle is computed. When the disc radius is large compared to the bulk correlation length, a correlation function of the surface charge density can be defined. It is checked, for the solvable models, that this correlation function does have the generic long-range behaviour, decaying as the inverse square distance, predicted by macroscopic electrostatics. In the case of a two-component plasma (a Coulomb fluid made of two species of particles of opposite charges), the density correlation function on the boundary circle itself is conjectured to have a temperature-independent behaviour, decaying as the −4 power of the distance.

We briefly examine the properties of dense plasmas characteristic of the atmospheres of neutron stars and of the interior of massive white dwarfs. These astrophysical bodies are natural laboratories for studying respectively the problem of pressure ionization of hydrogen in a strong magnetic field and the crystallization of the quantum one-component plasma at finite temperature.

Non-crystalline solids often emerge from melts with at least three atomic constituents. The study of packing aspects of melts that form glasses or quasi-crystals by investigating effective interactions in multi-component hard-sphere liquids is made possible by the geometrically based fundamental-measure density functional theory. It provides analytical approximations for the partial structure factors of the general m-component hard-sphere mixture (e.g. the Percus-Yevick approximation), and an accurate solution of the inverse scattering problem for obtaining the effective interactions. The fundamental-measure theory also enables one to extend such studies to more general (soft) interactions.

It has become clear that the self-consistent Ornstein–Zernike approximation (SCOZA) is a microscopic liquid-state theory that is able to predict the location of the critical point and of the liquid–vapour coexistence line of a simple fluid with high accuracy. However, applications of the SCOZA to continuum systems have been restricted up to now to liquids where the interatomic potentials consist of a hard-core part with an attractive two-Yukawa-tail part. We present here a reformulation of the SCOZA that is based on the Wertheim–Baxter formalism for solving the mean-spherical approximation for a hard-core–multi-Yukawa-tail fluid. This SCOZA version offers more flexibility and opens access to systems where the interactions can be represented by a suitable linear combination of Yukawa tails. We demonstrate the power of this generalized SCOZA for a model system of fullerenes; furthermore, we study the critical behaviour of a system with an explicitly density-dependent interaction where the phenomenon of double criticality is observed. Finally, we extend our SCOZA version to the case of a binary symmetric mixture and present and discuss results for phase diagrams.

A survey of the structural properties of a quasi-two-dimensional dipolar fluid is given with emphasis on the low-density regime where particles self-assemble into clusters. The internal energy, conformational properties and equilibrium length distributions of the clusters are measured by means of Monte Carlo simulation and compared with equilibrium polymer theory. The scaling forms of the length distribution functions predicted by theory are found to describe the simulation results adequately. The existence and mechanisms of phase transitions in dilute dipolar fluids are discussed.

Density (or state) dependent pair potentials arise naturally from coarse-graining procedures in many areas of condensed matter science. However, correctly using them to calculate physical properties of interest is subtle and cannot be uncoupled from the route by which they were derived. Furthermore, there is usually no unique way to coarse-grain to an effective pair potential. Even for simple systems like liquid argon, the pair potential that correctly reproduces the pair structure will not generate the right virial pressure. Ignoring these issues in naive applications of density dependent pair potentials can lead to an apparent dependence of thermodynamic properties on the ensemble within which they are calculated, as well as other inconsistencies. These concepts are illustrated by several pedagogical examples, including effective pair potentials for systems with many-body interactions, and the mapping of charged (Debye–Hückel) and uncharged (Asakura–Oosawa) two-component systems onto effective one-component ones. The differences between the problems of transferability and representability for effective potentials are also discussed.

Two examples of charged media in water are studied by numerical simulations: aqueous solutions of highly asymmetrical electrolytes (large and highly charged spherical particles surrounded by small and slightly charged counterions) and a swelling clay (charged plane sheets surrounded by small counterions). In the former example, Brownian dynamics (BD) showed that the mean number of counterions in the vicinity of polyions nearly balances the charge of the macroion and that the turnover of the small ions in this region is important. The effect of hydrodynamic interactions on the dynamics is weak for small ions but is great for macroions. On the other hand, the relative decrease of the macroion self-diffusion coefficients is more important than that of counterions. Moreover, the small ions retain a relatively high self-diffusion coefficient at the highest concentration, a concentration at which the macroions freeze. BD simulation was also used to obtain the distribution of counterions Na⁺ between the sheets of a fairly hydrated montmorillonite. The obtained profile was very similar to those we obtained by atomic simulations (Monte Carlo and molecular dynamics) and by a Poisson–Boltzmann treatment. It justifies the description of the solvent as a continuum as soon as the system is hydrated enough. However, for less hydrated states of the clay (mono-or bi-layer of water), only atomic simulations can bring exploitable information. We showed that, according to whether the counterion is Na⁺ and/or Cs⁺, the behaviours in the bihydrated clay are very different: although Na⁺ is easily hydrated and is located in the middle of the pores, Cs⁺ remains close to the negative surfaces of the sheets and its preferential paths along the surface sites can be underscored from obtained trajectories.

Considering the example of interacting Brownian particles we present a linear response derivation of the boundary condition for the corresponding hydrodynamic description (the diffusion equation). This requires us to identify a non-analytic structure in a microscopic relaxation kernel connected to the frequency-dependent penetration length familiar for diffusive processes, and leads to a microscopic definition of the position where the hydrodynamic boundary condition has to be applied. Corrections to the hydrodynamic limit are obtained and we derive general amplitudes of spatially and temporally long-ranged fluctuations in the diffusive system considered.

We use molecular dynamics computer simulations to study the relaxation dynamics of Na₂O–2(SiO₂) in its molten, highly viscous state. We find that at low temperatures the incoherent intermediate-scattering function for Na relaxes about 100 times faster than the one of the Si and O atoms. In contrast to this, all coherent functions relax on the same timescale if the wavevector is around 1 Å⁻¹. This anomalous relaxation dynamics is traced back to the channel-like structure for the Na atoms that have been found for this system. We find that the relaxation dynamics for Si and O as well as the time dependence of the coherent functions for Na can be rationalized well by means of mode-coupling theory. In particular, we show that the diffusion constants as well as the α-relaxation times follow the power law predicted by the theory and that in the β-relaxation regime the correlators obey the factorization property with a master curve that is described well by a von Schweidler law. The value of the von Schweidler exponent b is compatible with the one found for the above-mentioned power law of the relaxation times/diffusion constants. Finally, we study the wavevector dependence of f_s(q) and f(q), the coherent and incoherent non-ergodicity parameters. For the Si and O atoms these functions look qualitatively similar to the ones found for simple liquids and pure silica, in that the coherent function oscillates (in phase with the static structure factor) around the incoherent one and in that the latter is approximated well by a Gaussian function. In contrast to this, f(q) for Na–Na is always smaller than f_s(q) for Na and the latter can be approximated by a Gaussian only for relatively large q.

Most colloids usually exhibit one or several polydispersities. A natural framework for the theoretical description of polydisperse systems is provided by the extension of density functional theory to 'continuous' mixtures. This will be illustrated here by the study of both the bulk and interfacial properties of a simple van der Waals model for a polydisperse colloidal fluid.

The stochastic motion of a wall of mass M separating two semi-infinite cylindrical volumes filled with non-interacting point particles of mass m is studied. The initial equilibrium states on both sides are characterized by the same pressure but by different temperatures and densities. Frictionless motion of the wall is entirely due to collisions. In the scaling limit where the mass M grows as the surface area of the wall M ∼ L², L → ∞ and = 2m/(m + M) ∼ L⁻², the Ornstein–Uhlenbeck process is shown to govern the stochastic dynamics. In an inhomogeneous environment the wall behaves like a Brownian particle with an effective temperature determined by the ratio of the energy and particle fluxes. The global particle flux defines the dynamic friction coefficient. A comparison with predictions of Boltzmann's theory is presented, bringing in the subtle problem of the drift velocity.

A surface force balance has been used to investigate the viscosity of salt-free (conductivity) water confined between hydrophilic and between hydrophobic surfaces. We examine the process of jump-in, across the last few nanometres of thin water films, to adhesive contact between the surfaces. We analyse the flow of water out of the gap under slip and no-slip boundary conditions at the confining surfaces. In both cases we find that the effective viscosity of water remains comparable to its bulk value even when it is confined to sub-nanometre thin films.

The storage capacities of porous materials made up of carbon nanotubes are estimated by Monte Carlo simulations for the specific case of hydrogen in the pressure domain from 0.1 to 20 MPa at temperatures of 293, 150 and 77 K. The use of these materials in devices for hydrogen storage is discussed on the basis of the simulation results.

We present a theoretical study of capillary condensation of fluids adsorbed in mesoporous disordered media. Combining mean-field density functional theory with a coarse-grained description in terms of a lattice-gas model allows us to investigate both the out-of-equilibrium (hysteresis) and the equilibrium behaviour. We show that the main features of capillary condensation in disordered solids result from the appearance of a complex free-energy landscape with a large number of metastable states. We detail the numerical procedures for finding these states, and the presence or absence of transitions in the thermodynamic limit is determined by careful finite-size studies.

Two different levels of the free-volume approximation for the calculation of the phase diagram of a asymmetric hard-sphere mixture are compared to direct simulations of the phase behaviour. The mean-field-level free-volume approach, where only the statistically pre-averaged free volume is accounted for, is already in satisfactory agreement with the simulation results. Taking correlations into account within the free-volume approach improves the agreement with the solid branch of the phase diagram but, remarkably, this version performs somewhat worse for the fluid branch.

The highly asymmetrical primitive model of colloid–counterion mixtures is solved using the advanced integral equation proposed by Barrat et al(Barrat J L, Hansen J P and Pastore G 1988 Mol. Phys.63 747–67). The approximate bridge functions are expressed in terms of three-particle direct correlation functions, themselves derived from a factorization ansatz and thermodynamical relations. Comparisons with the bare HNC and previous improved closures as well as with recent Monte Carlo simulation data illustrate the efficiency of this equation for the precise determination of the structural and equilibrium properties of highly charged colloidal systems.

Since the early observation of nematic phases of disc-like clay colloids by Langmuir in 1938, the phase behaviour of such systems has resisted theoretical understanding. The main reason is that there is no satisfactory generalization for charged discs of the isotropic DLVO (Derjaguin, Landau, Verwey and Overbeek) potential describing the effective interactions between a pair of spherical colloids in an electrolyte. In this paper, we show how to construct such a pair potential, incorporating approximately both the non-linear effects of counter-ion condensation (charge renormalization) and the anisotropy of the charged platelets. We discuss the consequences for the phase behaviour of laponite dispersions (thin discs of 30 nm diameter and 1 nm thickness), and we present an investigation into the mesostructure via Monte Carlo simulations.

We describe a density functional theory for mixtures of hard sphere (HS) colloids and ideal polymers, the Asakura–Oosawa model. The geometry-based fundamental measures approach which is used to construct the functional ensures the correct behaviour in the limit of low density of both species and in the zero-dimensional limit of a cavity which can contain at most one HS. Dimensional crossover is discussed in detail. Emphasis is placed on the properties of homogeneous (bulk) fluid phases. We show that the present functional yields the same free energy and, therefore, the same fluid–fluid demixing transition as that given by a different approach, namely the free-volume theory. The pair direct correlation functions c_ij⁽²⁾(r) of the bulk mixture are given analytically. We investigate the partial structure factors S_ij(k) and the asymptotic decay, r → ∞, of the total pair correlation functions h_ij(r) obtained from the Ornstein–Zernike route. The locus in the phase diagram of the crossover from monotonic to oscillatory decay of correlations is calculated for several size ratios q = R_p/R_c, where R_p is the radius of the polymer sphere and R_c that of the colloid. We determine the (mean-field) behaviour of the partial structure factors on approaching the fluid–fluid critical (consolute) point.

The influence of an external field acting differently on the two constituents of a binary colloidal mixture performing Brownian dynamics is investigated by computer simulations and a simple theory. In our model, half of the particles (A particles) are pulled by an external force ^(A) while the other half (B particles) are pulled by an external force ^(B). If ^(A) and ^(B) are parallel and the field-free state is a mixed fluid, previous simulations (Dzubiella J et al 2002 Phys. Rev. E 65 021402) have shown a nonequilibrium pattern formation involving lanes of A or B particles only, which are sliding against each other in the direction of the external forces. In this paper, we generalize the situation both to nonparallel external forces and to field-free crystalline states. For nonparallel forces, lane formation is also observed but with an orientation tilted with respect to the external forces. If the field-free state is crystalline, a continuous increase of the parallel external forces yields a novel re-entrant freezing behaviour: the crystal first melts mechanically via the external force and then recrystallizes into demixed crystalline lanes sliding against each other.

We report new results on drainage and coarsening of aqueous foams. We show that these two effects can strongly interfere, enhancing the drainage velocity. Without coarsening, we have performed free-drainage experiments, in which local drainage rates are measured by electrical conductivity and by light scattering techniques. We have investigated the roles of the bubble size, of the surface and bulk rheology and of the liquid fraction. The results show that changing these foam parameters can induce transitions between different drainage regimes. The results are analysed in terms of two dimensionless numbers describing the balance between surface and bulk dissipation.

Understanding how macroscopic properties depend on intermolecular interactions for complex fluid systems is an enormous challenge in statistical mechanics. This issue is of particular importance for designing optimal industrial fluid formulations such as responsive oilfield fluids, based on viscoelastic surfactant solutions. We have carried out extensive molecular dynamics simulations, resolving the full chemical details in order to study how the structure of the lamellar phase of viscoelastic surfactant solutions depends on the head group (HG) chemistry of the surfactant. In particular, we consider anionic carboxylate and quaternary ammonium HGs with erucyl tails in aqueous solutions together with their sodium and chloride counterions at room temperature. We find a strong HG dependence of the lamellar structure as characterized by suitable pair correlation functions and density distributions. The depth of penetration of water into the bilayer membrane, the nature of counterion condensation on the HGs and even the order and correlation of the tails in the lamellae depend sensitively on the chemical details of the HG. We also determine the compressibility of the lamellar system as a first step to using atom-resolved molecular dynamics in order to link the molecular and macroscopic scales of length and time. The results give important insight into the links between molecular details and surfactant phase structure which is being exploited to develop more systematic procedures for the molecular design and formulation of industrial systems.

Molecular dynamics simulations using a coarse-grained (CG) model for dimyristoyl-phosphatidyl-choline and water molecules have been carried out to follow the self-assembly process of a Langmuir monolayer. We expand on a previous study of the characteristics of the CG model where we compare the rotational and translational constants of the present model to those of an all-atom (AA) model, and find that the rotational and translational timescales are up to two orders of magnitude faster than in an AA model. We then apply the model to the self-assembly of a Langmuir monolayer. The initial randomly distributed system, which consists of 80 lipids and 5000 water sites, quickly self-assembles into two Langmuir monolayers and a micelle in the bulk water region. The micelle slowly diffuses towards and fuses with one of the interfacial monolayers, leaving the final equilibrated state with a Langmuir monolayer at each of the two air/water interfaces. The effective speed-up gained from the CG approach gives access to timescales and spatial scales that are much larger than those currently accessible with AA models.

We present an overview of the recent progress that has been made in understanding the origin of hydrophobic interactions. We discuss the different character of the solvation behaviour of apolar solutes at small and large length scales. We emphasize that the crossover in the solvation behaviour arises from a collective effect, which means that implicit solvent models should be used with care. We then discuss a recently developed explicit solvent model, in which the solvent is not described at the atomic level, but rather at the level of a density field. The model is based upon a lattice-gas model, which describes density fluctuations in the solvent at large length scales, and a Gaussian model, which describes density fluctuations at smaller length scales. By integrating out the small-length-scale field, a Hamiltonian is obtained, which is a function of the binary, large-length-scale field only. This makes it possible to simulate much larger systems than was hitherto possible as demonstrated by the application of the model to the collapse of an ideal hydrophobic polymer. The results show that the collapse is dominated by the dynamics of the solvent, in particular the formation of a vapour bubble of critical size. Implications of these findings for the understanding of pressure denaturation of proteins are discussed.

This special issue of JPCM, devoted to liquid state theory, from white dwarfs to colloids reflects the scientific program of the conference that took place at the physics centre in Les Houches (France) in April 2002. This conference, as well as this special issue, had two purposes. The first one was to give a state-of-the-art picture of the current progress in the field of statistical physics of liquids, with its many applications. The second was to celebrate with Jean-Pierre Hansen the occasion of his 60th birthday.

In a standard textbook picture, the liquid phase occupies only a small portion of the phase diagram. Its importance in nature and in practical applications, is however, much greater than this simplistic view would suggest. The liquid state is of utmost importance to a number of physical, chemical, and of course biological phenomena. To give only a few examples, chemical reactions very often take place in solution, water is the universal biological solvent, soft condensed matter generally involves mixtures of liquids, surfactants and macromolecules. In a more speculative range, the behaviour of granular matter can also be reminescent of that of fluids.

Historically, a coherent picture of the liquid state developed much later than for solids or dilute gases. To quote V Weisskopf [1] `. . . theoretical physicists . . . probably would predict the existence of atoms, of molecules, of solid crystals, . . . but most likely not the existence of liquids'. The liquid state is a disordered and condensed state, for which systematically controlled perturbative approach are, in general, unsuccessful. Developing a theory for the liquid state generally involves bold, and not always controlled, approximations. Hence it is essential that the theory can be tested against `exact' results obtained for perfectly well controlled models. This specific feature explains the essential role that has been played in liquid state physics by computer simulation. In fact, the development of simulation methods is in itself an important theoretical activity, which in turn opens the way to new applications. Liquid state theory has developed, along the years, a distinctive way of combining theoretical and numerical approaches to understand the behaviour of more and more complex systems.

Theory of soft condensed matter is often approached from a different viewpoint, with emphasis on scaling ideas and coarse-grained descriptions. In many cases, however, a quantitative description will necessitate a mapping between these coarse grained approaches and a more microscopic description. Again an appropriate use of computer simulations and methods derived from the theory of liquids (integral equations, density functional theories) becomes relevant here.

The aim of the workshop was therefore be to bring together theoreticians working in various fields in which methods from the theory of liquids have been successfully applied. In spite of their common origin, these methods have undergone different developments, depending on the specific field of application. A good example of the cross-fertilization that can arise in such a context is density functional theory. In this field, ideas for simulating complex fluids have been borrowed from the electronic structure case and successfully used to model complex fluids [2].

As was mentioned above, the workshop and this special issue were also an opportunity to acknowledge the essential contributions made by Jean-Pierre Hansen to the theory of liquids. J-P Hansen has contributed to all aspects of the field, with applications to many different areas of physics. Examples include his work to the theory of charged fluids and plasmas, with results still widely used in astrophysical applications. His formulation of self-consistent integral equations allowed extension of these methods to strongly coupled fluids. Some of the first simulations of dynamical properties of supercooled fluids, that contributed to a better understanding of the glass transition. More recently, J-P Hansen extended his interests to the fields of complex fluids and granular matter. Another fundamental aspect of his contribution is of course on the pedagogical side, with the two successive editions of the book Theory of Simple Liquids with Ian McDonald, still the classical reference in the field.

As can be expected from the above introduction, a wide range of liquid-state topics were covered during the conference. The list of topics included

• Quantum fluids, plasmas, and astrophysical applications

• Structure of simple and complex fluids, integral equations

• Density functional theory and inhomogeneous systems

• Electrolytes and polyelectrolytes

• Transport coefficients, generalized hydrodynamics, kinetic theory

• Glasses

• Soft condensed matter: colloids, polymers, interfaces

• Complex molecules, biological liquids

• Granular systems

• Reactions in solutions

While no workshop can give a comprehensive view of the field, we hope that the contributions to this volume will provide a state-of-the-art survey of current theoretical concepts that relate to the physics and chemistry of the liquid state of matter. Despite the very broad scope covered, we hope it will also be an illustration of the underlying unity of the field, to which Jean-Pierre Hansen, through his scientific activity and personal leadership, has contributed a great deal.

Finally, we would like to thank the Les Houches conference sponsors (Commissariat a l'energie atomique, Centre National de la Recherche Scientifique, Ecole Normale Superieure de Lyon, Schlumberger Research, Unilever) and Richard Palmer from IOP Publishing who accepted our proposal to publish this special issue.

Jean-Louis Barrat, Hartmut Löwen and Gilles Zerah

Guest Editors

References

[1] Weisskopf V F 1977 Trans. N. Y. Acad Sci.38 2202

[2] Lowen H, Madden P, Hansen J-P 1992 Phys. Rev. Lett.68 1081

Rafael Agra Universite Paris-Sud

Angel Alastuey ENS Lyon

Ali Alavi Cambridge University

Rosalind Allen Cambridge University

Jean-Louis Barrat Universite Claude Bernard-Lyon 1

Marc Baus Universite Libre de Bruxelles

Laure Bellier-Castella Universite Claude Bernard-Lyon 1

Luc Belloni CEA/SACLAY

Bernard Bernu Universite Pierre et Marie Curie, Paris

Thierry Biben Universite Joseph Fourier, Grenoble

Lyderic Bocquet ENS Lyon

Edo Boek Schlumberger Cambridge Research

Peter Bolhuis University of Amsterdam

Daniel Borgis Universite Pierre et Marie Curie, Paris

David Ceperley CECAM---ENS-Lyon

Gilles Chabrier ENS-Lyon

David Chandler University of California, Berkeley

David Chapot ENS Lyon

Elisabeth Charlaix UCBL, Villeurbanne

Giovanni Ciccotti Universite `La Sapienza', Rome

Sergio Ciliberto ENS Lyon

Jean Clerouin CEA/DIF, Bruyeres Le Chatel

Robert Eisenberg Rush Medical Center, Chicago

Gerald Faussurier CEA/DIF, Bruyeres Le Chatel

Guillaume Ferlat Universite Claude Bernard-Lyon 1

Reimar Finken Cambridge University

Daan Frenkel FOM Institute, Amsterdam

Matthias Fuchs Institut Charles Sadron, Strassbourg

Jean-Pierre Hansen Cambridge Univeristy

Bernard Jancovici Universite Paris-Sud

Jean-François Joanny Institut Curie, Paris

Gerhard Kahl TU Wien

Jacob Klein Oxford University

Michael L Klein University of Pennsylvania

Walter Kob Universite Montpellier II

Vincent Krakoviack Cambridge University

Dominique Langevin Universite Paris-Sud

Hendrik Lekkerkerker Van t'Hoff Laboratorium, Utrecht

Dominique Levesque Universite Paris-Sud

Hartmut Löwen Heinrich-Heine-Universitat Dusseldorf

Paul Loubeyre CEA/DIF, Bruyeres Le Chatel

Ard Louis Cambridge University

Paul Madden Oxford University

Geoffrey Colin Maitland Schlumberger Cambridge Research

Michel Mareschal CECAM ENS-Lyon

Ignacio Pagonabarraga Universitat de Barcelona

Michele Parrinello CSCS/ETH, Zurich

Giorgio Pastore Universita di Trieste

Gren Patey University of British Columbia, Vancouver

Jaroslaw Piasecki University of Warsaw

Roy Pollock LLNL, Livermore

Yaakov Rosenfeld Nuclear Research Center Negev, Beer-Sheva

Jean-Noel Roux Laboratoire des Materiaux et des Structures du Genie Civil

Richard Sear University of Surrey

Christian Simon University of Pennsylvania

Enrico Smargiassi Università di Trieste

Berend Smit University of Amsterdam

Gilles Tarjus Universite Pierre et Marie Curie, Paris

Pieter Rein Ten Wolde FOM Institute, Amsterdam

Emmanuel Trizac Universite Paris-Sud

Pierre Edouard Turq Universite Pierre et Marie Curie, Paris

Willem Vos University of Amsterdam

Rodolphe Vuilleumier Universite Pierre et Marie Curie, Paris

Patrick Warren Unilever Research Port Sunlight

Jean-Jacques Weis Universite Paris-Sud

Peter Wolynes University of California, San Diego

Hong Xu Universite Claude Bernard-Lyon 1

Gilles Zerah CEA/DIF, Bruyeres Le Chatel

Jean-Pierre Hansen was born on 10 May 1942 in Luxembourg, into a family of civil servants and engineers. He grew up in Differdange, close to the imposing steel-works, where his father was in charge of Europe's largest rolling mill. In the 50s he attended the Athénée Grand-Ducal de Luxembourg, and enjoyed massive injections of Latin and Mathematics. His early passions were Astronomy and History of Art, but he followed paternal advice and went up to the Université de Liège in Belgium to take a degree in Engineering. After two years, under the influence of the leading astrophysicist Paul Ledoux, he switched to Physics and graduated in July 1964 with highest honours. Despite an offer from Cambridge, JPH decided to move to Paris for his PhD. He went to the recently created Orsay Campus of the University of Paris to obtain a `Doctorat de Troisième Cycle' under the guidance of Bernard Jancovici and Dominique Levesque, with whom he wrote his first paper on a quantum Monte Carlo study of solid He³ and He⁴. He then became a student of Loup Verlet and prepared his PhD (Doctorat d'Etat) under Verlet's masterful guidance, and defended his thesis entitled Contribution à l'Etude des Systèmes de Lennard-Jones classiques et quantiques in June 1969; his thesis examination committee was presided over by Jacques Yvon. In 1967, JPH had been appointed attaché de recherche at the Centre National de la Recherche Scientifique (CNRS) and he was duly promoted to chargé de recherche upon obtaining his PhD. Philippe Nozières had been designated JPH's mentor (parrain) at CNRS, and was to have a lasting influence throughout the latter's career in France.

JPH spent the academic year 1970-71 as a postdoctoral research associate at Cornell University, where he interacted with Neil Ashcroft, Geoffrey Chester, Jim Krumhansl, Mark Nelkin, Roy Pollock and Ben Widom among others. He also learned the meaning of `Upper New York State winters'. Attending various conferences in the USA, including the 11th Statistical Mechanics Conference in Chicago and the Liquids Gordon Conference in New Hampshire, he met many of the founding fathers of modern liquid state theory including Lars Onsager, Berni Alder, Joel Lebowitz, Jerry Percus and Bob Zwanzig, as well as some of his contemporaries who shared similar interests and who were to become life-long friends, particularly David Chandler, Mike Klein, Roy Pollock and Eduardo Waisman.

Upon returning to France, JPH turned his interest to high density (or strongly coupled) plasmas, with astrophysical applications. In 1973 he was appointed Professor of Physics at Université de Paris 6 (now Pierre et Marie Curie), where he joined the small Laboratoire de Physique Théorique des Liquides headed by Savo Bratos. They started the post-graduate course on liquids, which is now very popular with students from all over Paris. JPH ran a small but lively research group on liquids, attracting excellent students (the first two to obtain their PhD were Patrick Vieillefosse and Bernard Bernu) and eminent visitors (Mike Klein, Ian McDonald, Yasha Rosenfeld and Lennard Sjögren in the early days). He joined forces with Ian McDonald to produce two editions of Theory of Simple Liquids. JPH later spent a very successful sabbatical year 1980-81 with Philippe Nozière's theory group at the European neutron scattering facility ILL in Grenoble, where he met Herbert Capellman, Duncan Haldane, Alan Griffin, and John Hayter, who stimulated JPH's interest in colloidal systems. Upon returning to Paris he became scientific adviser at the Limeil Centre of the Commissariat à l'Energie Atomique, where he supervised the PhD work of Gilles Zerah and others, and had a long-lasting collaboration with Jean Clérouin, in a joint project with Philippe Choquard's group in Lausanne.

In the early 80s, JPH had his arm sufficiently twisted by Philippe Nozières and others to agree to move to Lyon and help create the new Ecole Normale Supérieure. In the French context, creating a major Grande Ecole outside Paris was considered a risky business, and volunteers from the `establishment' were in short supply. JPH moved to Lyon in 1987 with a handful of daring young scientists (Claude Laroche and JPH being the only senior members), including Jean-Louis Barrat and Stephan Fauve, to create the Laboratoire de Physique de l'Ecole Normale Supérieure de Lyon, now one of the most thriving Physics Departments in France. With Bernard Bigot, JPH also served for five years as Deputy to the first Director of the Ecole, Guy Aubert. The success of the Ecole has gone beyond the wildest expectations, and now regularly diverts some of the best science students in France from rival Schools in Paris. In a `conspiracy' with Giovanni Ciccotti and others, JPH helped in transferring CECAM from Paris to Lyon.

JPH's group at ENS-Lyon thrived, and enjoyed collaborations with numerous visitors, including David Chandler, Mike Klein, Hartmut Löwen, Paul Madden, Jarek Piasecki and Hiroo Totsuji, in work on the glass transition, Brownian motion, dense plasmas and colloidal dispersions.

In 1990 the First Liquid Matter Conference took place at ENS-Lyon, attracting an unexpected 600 participants (and requiring the hasty installation of large tents for parallel sessions). The same year JPH was awarded the Grand Prix de l'Etat of the Académie des Sciences, and in 1992 he was elected to the Institut Universitaire de France. During spring of 1991 he spent several fruitful and sunny weeks with David Chandler's group in Berkeley, where he had been appointed Miller Visiting Professor. In 1994-95 he spent a productive and pleasant sabbatical year at Oxford with Mark Child, David Logan, Paul Madden and John Rowlinson, on a Visiting Fellowship at Balliol College. This visit stimulated his interest both in clay dispersions, and in the Oxbridge Collegiate system.

Having served ten eventful years in Lyon, JPH decided that it was time to move on. In 1996 he was elected to the 1968 Chair of Chemistry at Cambridge, previously held by John Lennard-Jones, Christopher Longuet-Higgins and David Buckingham. He moved to Cambridge in 1997 as Head of the Theoretical Chemistry Sector of the Department. His own group started off with his first Cambridge student, David Goulding, and first postdoc, Ard Louis; it has grown to a respectable (but reasonable) size, including distinguished Schlumberger Visiting Fellows, working on Statistical Mechanics of complex fluids and biomolecular assemblies. The Société Française de Physique awarded him in 1998 the Prix Spécial, in recognition of the scientific work he carried out in France over a period of 33 years. JPH is a Fellow of one of Cambridge's oldest Colleges, Corpus Christi, and serves as Deputy Head of the Department of Chemistry. JPH considers the life of a Physicist in a Chemistry Department to be stimulating and pleasant, and March 2002 saw the inauguration by the Vice Chancellor of the Cambridge University Centre for Computational Chemistry, created by JPH and his Theoretical Chemistry colleagues. On 9 May 2002, one day prior to his 60th birthday, JPH was elected Fellow of The Royal Society.

Outside of science, JPH enjoys visiting art exhibitions and Italian architectural marvels with his wife Martine, swimming and cycling with their grandson Gregory at their sea-side retreat in Port-Navalo (Southern Britanny), as well as listening to music by Mozart, Purcell and other great composers.

Occasionally he returns to his native Luxembourg (of which he has faithfully remained a citizen) to visit his brother and admire one of Europe's most remarkable and little-known medieval cities.