D. Levesque

Bio: D. Levesque is an academic researcher. The author has contributed to research in topics: Dynamic Monte Carlo method & Hybrid Monte Carlo. The author has an hindex of 1, co-authored 1 publications receiving 250 citations.

Perturbation theory for mixtures of simple liquids

Abstract: The perturbation approach developed by Weeks, Chandler, and Andersen (WCA) and by Verlet and Weis (VW) for pure systems is here generalized to the case of mixtures. We study binary mixtures of molecules interacting with the 12–6 Lennard-Jones potential, for which Monte Carlo simulations are available for comparison. The work is divided into two parts: The first part presents results of Monte Carlo calculations on mixtures of hard spheres of 864 and 1000 particles. The radial distribution functions generated are used to test the VW representation for the correlation functions of hard-sphere mixtures. This representation is found to work satisfactorily within the expected error limits. The second part deals with the two-step perturbation procedure for calculating the thermodynamic quantities of the Lennard-Jones system. The Lennard-Jones potential is divided into a reference potential, which is strictly repulsive, and an attractive part. The system of the reference potential is represented by a system of ha...

Structures of hard-sphere fluids from a modified fundamental-measure theory

Abstract: We reformulate Rosenfeld’s fundamental-measure theory using the excess Helmholtz energy density from the Boublik–Mansoori–Carnahan–Starling–Leland equation of state instead of that from the scaled-particle theory. The new density functional theory yields improved density distributions, especially the contact densities, of inhomogeneous hard-sphere fluids as well as more accurate direct and pair correlation functions of homogeneous hard spheres including those of highly asymmetric mixtures. This new density functional theory will provide an accurate reference for the further development of a statistical-thermodynamic theory of complex fluids at uniform and at inhomogeneous conditions.

Segregation and immiscibility in liquid binary alloys

Abstract: An overview of the thermophysical properties of segregating and demixing liquid binary alloys is presented encompassing the simple approaches that are commonly used by physicists, chemists and metallurgists in general. The various experimental and theoretical information available for such systems are put together to establish a respectable understanding between the experimental results, theoretical approaches and the empirical models. The key to understanding is the deviation that the properties exhibit from Raoult's law and the marked change in the liquid phase as a function of composition, temperature and pressure. The characteristic behaviour is ascribed to an outcome of the interplay of the energetic and structural re-adjustment of the constituent elements on mixing. After summarizing the experimental technique and some results, a comprehensive microscopic approach, based on statistical, electronic and hard sphere-like theory, is undertaken to further the understanding of the origin of the intriguing processes that are associated with the immiscible and phase-separating liquid alloys. We conclude by providing a brief account of the kinetic aspects of phase separation with some intended industrial applications.

Monte Carlo study of a phase‐separating liquid mixture by umbrella sampling

Abstract: Recently developed nonphysical sampling methods—umbrella sampling—have been used to obtain the free energy and other properties of a binary liquid mixture exhibiting phase separation with an upper critical solution point. The system is a mixture of two identical Lennard‐Jones liquids in which the interactions between the components are characterized by a range parameter σ12 obeying the Lorentz rule, but an energy parameter e12= (1−α) (e11e22)1/2 violating the Berthelot rule. The sampling methods enable one to cover wide ranges of temperature and composition with few Monte Carlo experiments, successfully sampling the metastable regions and obtaining the coexistence curve. The case α=0.25 is studied in detail, and compared with some theoretical predictions. An estimate is made of the minimum value of α required for phase separation at low pressures.

Additive and non-additive hard sphere mixtures

Abstract: Binary mixtures of additive (d 12 = (d 1 + d 2)/2) and non-additive (d 12 ≠ (d 1 + d 2)/2) hard spheres have been studied with new integral equations. Accurate Monte Carlo results for some non-additive cases have been generated and tables of radial distribution functions are explicitly given. Comparison of structural and thermodynamic results demonstrates that an approximate integral equation recently proposed by Martynov and Sarkisov for one-component hard spheres significantly improves on the Percus-Yevick approximation also in the mixture case, without introducing free parameters. A simple further generalization gives a very good parameterization of the computer experiment results. An analytical fit of the equation of state for symmetric non-additive systems is also given.