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Hierarchical Methods for Dynamics in Complex Molecular Systems


Generating and analyzing the dynamics of molecular systems is a true challenge to molecular simulation. It includes processes that happen on the femtosecond scale, such as photoinduced nonadiabatic (bio)chemical reactions, and touches the range of seconds, being e.g. relevant to cellular processes or crack propagation. Thus, many orders of magnitude in time need to be covered either one by one or concurrently. In the latest edition of this series of Winter Schools we addressed the topic of Multiscale Simulation Methods in Molecular Sciences in 2009 with a strong focus on dealing with a wide range of length scales. Now, instead, the key issue is to dwell on hierarchical methods for dynamics having primarily in mind systems described in terms of many atoms or molecules. One end of relevant time scales certainly is nonadiabatic quantum dynamics methods, which operate on the subfemtosecond time scale but influence dynamical events that are orders of magnitude slower. Examples for such phenomena might be photoinduced switching of individual molecules, which results into large-amplitude relaxation in liquids or photodriven phase transitions of liquid crystals. The other end of the relevant time scales are methods to investigate and understand the non-equilibrium dynamics of complex fluids, with typical time scales in the range from microseconds to seconds. Examples are the flow of polymer solutions, or the flow of blood through microvessels.

This Winter School has a daily stratification pattern starting with dynamics within the realm of Materials Science with a focus on slow processes which nevertheless require most detailed input at the level of electronic structure and interatomic potentials. In Biomolecular Science one challenge is the concurrent handling of an electronic structure based description of a 'hot spot' within an enzyme with a computationally efficient treatment of the protein environment in terms of parameterized interactions. Accelerated sampling is a key issue whenever both slow and fast motion is relevant such as metadynamics, force probe molecular dynamics or nonequilibrium dynamics using fluctuation theorems. Finally, getting rid of atoms and molecules but still keeping a particle perspective is achieved by coarse-graining procedures. In Soft Matter and Life Science, the dynamics is often governed by the hydrodynamics of the solvent. A particular challenge is here to bridge the large length- and time-scale gap between the small solvent molecules and the embedded macromolecules or macromolecular assemblies (polymers, colloids, vesicles, cells). Therefore, several mesoscale simulation approaches have been developed recently, which rely on a strong simplification of the microscopic dynamics with a simultaneous implementation of conservation laws on mass, momentum and energy. Here, Lattice Boltzmann, Dissipative Particle Dynamics and Multi-Particle Collision Dynamics are most prominent.

Last but not least most efficient implementation on current-day hardware is a must, which requires facing parallel computing issues when designing de novo software and porting well-established numerical codes like DUNE (Distributed and Unified Numerics Environment) or numerical methods like the multigrid method onto new architectures. In addition to lectures and poster sessions this Winter School will offer an introductory course to parallel computing with practical sessions.