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Project A10 (New): Population control of multiple walker simulations via a birth/death process Conventional Molecular Dynamics (MD) simulations are generally unable to access the long-timescale phenomena that are common in nature. This timescale problem comes from the fact that a typical free energy landscape consists of many metastable states separated by high free energy barriers. If the barriers are much higher than the thermal energy, the system is kinetically trapped in some metastable state and barrier crossings will be rare events on the time scales that we can simulate. One strategy to alleviate this time scale problem is to employ collective variable (CV) based enhanced sampling methods such as metadynamics. A common way to improve the performance of CV-based methods is to employ multiple walkers that share a bias potential and collaboratively sample the free energy landscape. In this way, one reduces the wall-clock time for convergence and makes better […]

Prof. Dr. Thomas Speck Institut für Physik Universität Mainz Staudingerweg 9 D-55128 Mainz Tel: +49 6131 39 26915 Fax: +49 6131 39 20496 Mail: thomas.speck@uni-mainz.de Further information

Prof. Dr. Omar Valsson Department of Chemistry University of North Texas 1155 Union Circle #305070 Denton, Texas 76203 Tel: +1 940 369 7593 Mail: omar.valsson@unt.edu Further information

Project C7: Dense active suspensions in the chaotic regime Active matter has become a quickly evolving field spanning from biology and physics to chemistry and engineering. Its defining property is the directed motion—translational, rotational, or both—of its constituents. This directed motion requires the steady input of free energy. Freed from the constraints of thermal equilibrium, active matter exhibits a wide range of novel phenomena; on the level of its single constituents up to emergent many-body collective and dynamic behavior. Extensively studied have been the aggregation of active particles into clusters, swarms, and other highly collective and dynamics states; but also spontaneous flow states where sufficiently high activity triggers the transition from a quiescent to a flowing fluid. At high densities, chaotic behavior has been reported in suspensions of bacteria and in numerical simulations. The aim of this project is to develop a comprehensive multiscale framework that bridges the properties of […]

Project C8: Numerical approximation of high-dimensional Fokker-Planck equations Stochastic processes driven by Brownian motion, which play a fundamental role in soft matter physics, can also be described by associated deterministic Fokker-Planck equations for probability distributions, where the dimensionality of the space on which this equation is posed increases linearly with respect to the number of particles. The aim of this project is to develop numerical solution methods for such high-dimensional problems that allow for the efficient extraction of quantities of interest, which typically take the form of certain integrals with respect to the computed distributions. In the high-dimensional case, beyond the basic numerical feasibility, a central issue is to ensure the accuracy of the computed solutions by suitable a posteriori error control. The initial focus of the project, which started during the second funding period, was on the development of numerical methods. On the one hand, we considered adaptive low-rank […]

Project A7: Dynamical coarse-graining for non-equilibrium steady states with stochastic dynamics Preserving dynamic information such as diffusion coefficients and transition rates in coarse-grained models is a persistent challenge in multi-scale simulations. This task becomes even more daunting when the original microscopic dynamics breaks detailed balance, corresponding to the system being driven away from thermal equilibrium. The aim of this project is to develop a comprehensive computational method to coarse-grain models from atomistic resolution to a few discrete states while preserving the statistics of the energetic exchange with their environment. In complex macro and biomolecules, these discrete states are identified with long-lived molecular conformations. In the second funding period, we are addressing the question how to model transitions that go beyond simple conformational transitions and involve a chemical transformation. To this end, we study a molecular rotor that is driven by light and performs asymmetric photoisomerization steps to achieve directional rotation. […]