CECAM - Simulations of hard bodiesSimulations of hard bodies

It is currently possible in an efficient way to calculate the distance between two hard convex objects with a generic shape and to predict their collision [ED4HB]. The first application of such algorithms has been tested on the molecular dynamics of a systems of classical hard ellipsoids of revolution [DeMicheleHE06]. The same methods allows to simulate shaped step interactions[DeMichelSticky06]. The recent introduction of an algorithm for the rotation of objects with a generic inertia tensor completes such approach [vanZonCondMat]. Moreover,following the lines of [BD4HS], it seems to be possible to extend classical Molecular Dynamics simulation to the Brownian Dynamics simulation of interest in the field of colloids and suspensions. A renewed interest for assemblies of hard shaped objects stems from the field of colloidal science; nevertheless,simulations of the dynamics of hard objects [Allen89,Allen93] needs to be revived and theoretical investigations on the dynamics of shaped objects reconsidered. Besides, we believe that there is a potential interest in several cross-disciplinary scientific and technological fields. Such belief stems from an analysis of the current investigations in several fields: * theory of molecular liquids: while hard-spheres are widely understood and form the reference system for many theories of the dynamics and the statics, there no such understanding for shaped objects [GrayGubbinsBook] * granular fluids: simulations of shaped particles are practically limited to hard needles * geo-mechanics: soil rheology employs mostly models and simulations where grains are spherical or, in the most sophisticated cases, ellipsoidal [Ouadfel99,Ouadfel01]. The new rheology introduced by switching from spheres to elongated objects should induce to take account of shape as a must, not as an optional. * powders: same situation than in geo-mechanics [Ouadfel99,Antony04]. * fruit & vegetables: damages due to processing, transportation and handling are studied via simulations of spheres that represent potatoes, tomatoes, apples [LoodtsMSTh]. Damages are predicted looking at the collision points on the spheres; from our experience on ellipsoids, we believe that at least the collision frequency and the magnitude of the impact is deeply influenced even by a little elongation of the objects. Moreover, experiments for the mechanical characterizations require at least a description in terms of an ellipsoidal object [Cherng05]. * colloids and nanoassembly: despite the possibility of controlling the shape of the particles [vanDillen2004], hard spheres remain the main reference system. * lyotropic liquid crystals: several overlap criteria [Allen93,Het99,Blaak99] allow the simulation of specific hard objects and point out the importance of the shape on the appearance of new liquid-crystal phases. No general method to investigate and quantify such effect exists for at least convex objects. * coarse-grained proteins: from experimental data, at least Human Serum Albumin can be modeled as an hard ellipsoid with a repulsive stepwise potential [Sjoberg97]. * go-models [Go83] for folding: rigid sub-sequences of a protein could be modelled by a single shaped unit speeding up the simulations. * computer science, computer graphics, game design, robotics, virtual reality: distance calculations and collision prediction are the core for the realization of virtual environments and robotic manipulations; again, most algorithm are specific and not shape-independent [Ju01,Eberly01]. In conclusion, we believe that it is timely to promote a cross-disciplinary meeting on the subject in order to create an enlarged community sharing the same interests on simulating hard bodies

Simulations of hard bodies

Location: CECAM 46 allée d'Italie 69007 Lyon France

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