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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 A4 (Completed): Understanding Water Relaxation Dynamics at Interfaces The aim of the project is to develop multiscale approaches to understand the mechanisms of vibrational energy relaxation in water at interfaces and in confined environment. In the first funding period, we have developed an efficient method to describe molecular vibrational relaxation based on single molecule excitations and the use of new descriptors. In the second funding period, we plan to include nuclear quantum effects (NQEs), which may be important in water. We aim to develop a multi resolution scheme where the electronic structure is included with an effective force field, which accurately reproduces high-level ab initio calculations, while the NQEs are explicitly addressed with the path integral formalism. This project has ended in June 2022.

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 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 […]

Project A9: Coarse grained non-equilibrium dynamics of active soft matter Active colloids can self-propel in an unbiased solvent and provide a paradigmatic example of non-equilibrium soft matter. They have received enormous attention in recent years, partly for their rich ability to form dynamic structures such as living crystals, self-organized super-rotor assemblies, and travelling wave patterns. To a large extent, these dynamic structures are now known to hinge on the unusual hydrodynamic interactions among active colloids as well as on the phoretic cross-interactions which hinge on the action of a phoretic field (concentration, temperature) gradient due to a certain colloid on other colloids in the system. These interactions are in general long-ranged, confinement-dependent, non-reciprocal, non-instantaneous and non-pair-wise. However, despite their importance in generic experiments with active colloids, many key aspects of these interactions are still not well understood. To improve our corresponding understanding, the overarching goal of the present project is […]

Project B1: Inverse problems in coarse-grained particle simulations Coarse-graining (CG) methods are an indispensable tool in computational materials science, but the associated upscaling and downscaling processes have to be designed with great care to allow for a proper interpretation of the computed results. Each of these interscale transfers comes along with important inverse problems to be resolved, most of which are ill-posed, or ill-conditioned at the very least. The purpose of this project is to apply rigorous techniques from the mathematical field of inverse and ill-posed problems to attack these fundamental problems in the multiscale simulation of soft matter, and to provide a mathematically rigorous foundation of existing and/or new upscaling processes. n the first two funding phases we have developed the mathematical foundation for a rigorous analysis of iterative methods that are currently being used for the computation of effective pair potentials of sophisticated CG models. We have used […]

Integrated research training group (IRTG) The integrated research training group (IRTG) of the TRR 146 provides a joint structured graduate education in the area of Computational Materials Science for the graduate students and young postdocs in the TRR 146 as well as other interested candidates working in related areas. The goals of the IRTG are threefold: 1) to provide students with the interdisciplinary background required for the research activities in the TRR 146, and to prepare them for a possible career in the area of theoretical Materials Sciences 2) to ensure common standards in the education of all graduate students in the TRR 146 by means of a well structured supervision and management program, 3) to establish and strengthen links within the TRR 146 already at the level of graduate students and young postdoctoral researchers. Special emphasis is placed on promoting exchange between groups within and outside of the TRR […]