Théorie et Simulation

« Chemically constrained systems : New perspectives from nanothermodynamics »

Présenté par Jean-Marc SIMON
Laboratoire Interdisciplinaire Carnot de Bourgogne,
Université de Bourgogne Franche Comté
Small systems cannot be described by classical thermodynamics. One reason is that the surface area becomes important, in contrast to the case for systems in the thermodynamic limit. The increased experimental interest in nanosized systems, has created a demand on the theoretical side. Our aim has been to find a systematic description of the thermodynamic properties of small systems; their size and shape-dependence in particular. Thereby we hope to improve the understanding and modeling ability of such systems. The thermodynamics of small systems (also called nanothermodynamics) was first developed by T. L. Hill [1] in the sixties. It gives a general background to systematically express thermodynamic properties in terms of system size [2]. During the last 5 years we applied this approach to the analysis of molecular dynamics simulations and we developed new efficient tools to compute thermodynamic properties like partial molar quantities that can be hardly accessible by other methods. The method was tested on different system types: Lennard-Jones mixtures, ternary molecular systems, reactive mixtures (2H=H2), CO adsorbed on graphite, … These results validate the use of the thermodynamics of small systems for molecular systems and clearly show that they are consistent both with the Kirkwood-Buff approach [3, 4] and Gibbs’ thermodynamics for a surface. Beyond the application to molecular simulated data, this new approach opens new ways to study systems were the individual particle sizes are large compared to the system size. During the presentation I will present the way we applied nanothermodynamics for the benefit of the analysis of molecular simulations, and I will put a focus on the analysis of chemically constrained systems. [1] T. L. Hill. Thermodynamics of small systems. Part 1, Benjamin, New York, 1963