Search Results

This section is still under development. A list of all publications until 2021 can be found here.

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 A3: Coarse-graining frequency-dependent phenomena and memory in colloidal systems The purpose of this project is to develop numerical strategies for dynamic coarse-graining in situations where the separation of time scales is incomplete and memory effects are important. This entails the reconstruction of coarse-grained dynamical equations that include memory (generalized Langevin equations, GLE), the efficient simulation of coarse-grained models with memory and the application to colloidal dispersions at equilibrium and non-equilibrium. This project is complementary to project A2, where related problems are addressed in the context of dynamic coarse-graining of molecular liquids. In the second funding period, we have extended our previous work on iterative memory reconstruction for single colloids (first funding period) to systems containing multiple colloids, where pair memory effects must be taken into account. A benchmark simulation of 125 colloids in solution showed that a speedup of at least three orders of magnitude can be obtained by […]

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 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 […]

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 […]

Projects B: Particle based coarse-graining and mixed resolution schemes • B1: Inverse problems in coarse-grained particle simulations • B2: Many-body effects and optimized mapping schemes for systematic coarse-graining • B3: Coarse-graining of solvent effects in force-probe molecular dynamics simulations • B4: Equilibrium and non-equilibrium processes in open systems via adaptive resolution simulations • B5: Multi-resolution methods including quantum chemistry, force fields, and hybrid particle-field schemes • B6: Topological validation of coarse-grained polymer models • B7: Machine learning for multiscale simulations • B8 (N): Hydrodynamic Simulation of Passive and Active Janus Particles