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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 […]

Admission and Qualification Admission Students funded directly by the TRR146 are automatically admitted to the IRTG. External students can apply for admission by presenting a CV and a one-page project plan to the TRR146 Office where they explain how their project fits TRR146 topics. The application will be evaluated by the PIs of the IRTG. We anticipate that workshop and conference travel funding for admitted external students will be limited and accessible only upon application. Qualification plan The most important training element of the IRTG is the research on the project, assisted by efficient supervision . In addition, the integrated training group serves as a mean to provide students and young postdoctoral researchers with the training required for working within the CRC-TR. The training is made necessary by the interdisciplinary nature of the CRC-TR, where chemistry, physics, mathematics and computer science are intertwined in a non-standard combination, which is usually […]

IRTG – Activities The IRTG fosters its objectives through a series of activities (see items below), which the members can attend/exploit in relation to their needs. Participation to the activities of the IRTG should not require more than 15% of a student’s working time. The activities are coordinated by the coordination office of the CRC-TR together with the elected student/postdoc speakers.

IRTG Organization Currently, the student/postdoc speakers are • Rebecca Steiner (further information) • Fabio Frommer (further information) • Moritz Mathes (further information) • Maarten Brems (further information)

Project A2: Dynamically consistent coarse-grained models The aim of this project is to develop methods that endow chemically-specific coarse-grained (CG) simulation models with consistent dynamical properties. To this end, CG models with conservative and dissipative interactions are derived from a higher-resolution model using bottom-up coarse-graining methods that retain a highmlevel of chemical specificity. In the first two funding phases, we have developed methods for deriving Markovian and non-Markovian CG models that successfully represent the dynamics of molecular liquids, polymer solutions, and star-polymer melts on diffusive time scales. The Markovian method uses a dissipative particle dynamics (DPD) thermostat that is parameterised by means of a bottom-up approach using the microscopic dynamics. While successful in CG simulations of molecular liquids where only the friction due to the relaxation of atomic vibrations needs to be accounted for, it fails to describe the dynamics of polymer melts and the dynamics of small molecules in […]

Project A5 (Completed): Heat transfer in polymer nanocomposites A multiscale approach to heat transfer in soft matter will be developed. In particular, coarse-grained models of polymer nanocomposites including graphite flakes will be built and employed to obtain and characterize relaxed structures of such materials. Atomistic details will be reinserted in these structures and heat transfer will be characterized at this level of description to obtain reference data. Then, the question will be addressed how the coarse-grained models have to be modified in order to characterize heat transport in the nanocomposites directly at the coarsened level of description. This project has ended in June 2018.

Project A6: Coarse-grained models for dynamically asymmetric liquid mixtures under non-equilibrium conditions he main goal of this project is to gain better insight into the mapping of time-dependent properties of complex molecular systems, when studied using multiscale simulations. While the mapping of length scales is inherently defined by the coarse-graining procedure, the mapping of dynamic processes involves a complex combination of factors due to both the removal of degrees of freedom as well as approximations made in determining the coarse-grained (CG) interactions based on a reference all-atom (AA) model. As a consequence, the development of dynamically-consistent CG models is particularly challenging when various dynamic processes on different time scales coexist. To investigate these issues, we have focused on two important classes of systems, liquid crystals (LCs) and ionic liquids (ILs), which pair technological relevance with appropriate dynamics, and still show well defined modes of motion despite their significant complexity. In […]

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. […]

Project A8: Roberto – Improved dynamics in hybrid particle-field molecular dynamics simulations of polymers We pursue one of the approaches to generate coarse-grained polymer models with correct dynamical properties. If such models can be made predictive for, say, polymer melt viscosities and other rheological characteristics they will make their important contribution toward, e.g., energy-efficient plastics processing or mechanical recycling of plastics waste. In funding period 2 (FP2), we have developed and implemented the Roberto method, a combination of hybrid-particle-field (hPF) molecular dynamics and slip-springs. The hPF method by itself is computationally fast, yet it allows coarse-grained or even atomistic accuracy for the base models. It performs excellent for static polymer properties, but provides a qualitatively wrong molecular mobility. As the field treatment of intermolecular interactions makes them effectively soft-core, atoms can superpose, and polymer chains can cut through one another. The artificial dynamics is remedied by the slip-springs, which restore […]