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Dr. Florian Müller-Plathe
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Multiscaling and Transport in Polymer Science
The problem of multiscaling or coarse-graining is particularly difficult for polymers, as chain connectivity prevents the system from conveniently and naturally separating into building blocks. Nonetheless, there has been some success in recent years to connect the atomistic (building block: 1 atom) to the mesoscopic scale (building block: ~1 monomer), in addition to bridging other levels [1]. Such mesoscopic models can be derived from preceding atomistic simulations in a such way that the mesoscale model retains much of the chemical identity of the parent atomistic model [2]. In other words, the mesoscale model is specific for every real polymer and for every situation (melt, solution, etc.); it is not a generic polymer model. The scheme has been automated in much the same spirit as earlier methods for generating atomistic force field parameters from experimental information [3]. The use of multiscale modelling in polymers is two-fold: Firstly, we want to predict macroscopic materials properties from a fundamental theory. Secondly, we use mesoscopic models together with remapping as equilibration highways for generating well relaxed atomistic structures. A number of applications will be presented.The second part of the lectures reviews non-equilibrium methods for calculating transport coefficients, with emphasis on the reverse non-equilibrium molecular dynamics method. It has fundamental and technical advantages over previous equilibrium and non-equilibrium techniques. For example, it applies the perturbation in a microcanonical way (no thermostat needed) and its raw data are well defined and robust gradients, rather than, fluxes which are often difficult to define and to calculate with sufficient accuracy. The method has so far been applied to the calculation of viscosities [4], thermal conductivities [5] and Soret coefficients [6].
[1] J. Baschnagel, K. Binder, P. Doruker, A.A.Gusev, O. Hahn, K. Kremer, W.L. Mattice,
F. Müller-Plathe, M. Murat, W. Paul, S. Santos, U.W. Suter and V. Tries, Adv. Polym.
Sci. 152, 41-156 (2000).
[2] H. Meyer, O. Biermann, R. Faller, D. Reith and F. Müller-Plathe, J. Chem. Phys.
113, 6265-6275 (2000); D. Reith, H. Meyer, and F. Müller-Plathe, Macromolecules 34,
2235-2245 (2001); R. Faller and F. Müller-Plathe, Polymer 43, 621-628 (2002).
[3] R. Faller, H. Schmitz, O. Biermann and F. Müller-Plathe, J. Comput. Chem. 20,
1009-1017 (1999).
[4] F. Müller-Plathe, Phys. Rev. E 59, 4894-4899 (1999).
[5] F. Müller-Plathe, J. Chem. Phys. 106, 6082-6085 (1997).
[6] D. Reith and F. Müller-Plathe, J. Chem. Phys. 112, 2436-2443 (2000); P. Bordat, D.
Reith and F. Müller-Plathe, J. Chem. Phys. 115, 8978-8982 (2001).