Search Results

2019 – Publications

Project B8 (N): Hydrodynamic Simulation of Passive and Active Janus Particles Janus particles are colloidal particles whose surface has been modified differently in different locations, creating so-called patches. The patches are designed in a way to generate directional interactions between the Janus particles. Janus particles, therefore, often self-assemble into ordered structures, commonly referred to as lattices or crystal structures, even though the system still is a colloidal solution. By variation of the chemical nature, size and location of the patches, a rich set of lattice structures is accessible. In our work so far, we have focused on triblock Janus particles, which carry attractive van-der-Waals patches on the poles and repulsive electrostatic charges around the equator. We developed a detailed dissipative-particle dynamics model for them, which includes surface chemistry and explicit solvent molecules. With this model and our newly devised adaptive metadynamics method, we could clarify their self-assembly into two-dimensional ordered […]

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. Burkhard Dünweg Max Planck-Institut für Polymerforschung Ackermannweg 10 D-55128 Mainz Tel: +49 6131 379198 Mail: duenweg@mpip-mainz.mpg.de Further information

Prof. Dr. Florian Müller-Plathe Institut für Physikalische Chemie Technische Universität Darmstadt Alarich-Weiss-Str. 8 D-64287 Darmstadt Tel: +49 6151 16-22621 Fax: +49 6151 16-22619 Mail: f.mueller-plathe@theo.chemie.tu-darmstadt.de Further information

Student initiatives The IRTG encourages doctoral students to pursue own ideas, take own initiatives, and to prepare and submit corresponding short proposals. This aims to foster student’s independence and scientific vision of their field of research, and also help them to gain first experiences with preparing proposals in order to obtain support for their research. Two specific sets of student initiatives described below are supported explicitly. Applications for research assistants The IRTG encourages the doctoral students to apply for undergraduate student research assistants. This will help them to develop their supervision skills. Applications to fund an undergraduate student research assistant in connection with a project are considered by the IRTG once per year. Groups of students and postdoctoral researchers need to prepare such projects on topics of shared interest. Each project will be presented to the assembly of students and discussed, e.g. after one of the students’ seminars. In addition […]

Project C3: Spinodal decomposition of polymer-solvent systems We consider the phase separation of dynamically asymmetric mixtures, in particular polymer solutions, after a sudden quench. Crucial aspects are (i) hydrodynamic momentum transport and (ii) the lack of time-scale separation between molecular relaxation and coarsening. This gives rise to complex dynamical processes such as the transient formation of network-like structures of the slow-component-rich phase, its volume shrinking, and lack of dynamic self-similarity, which are frequently summarized under the term viscoelastic phase separation. The relevant length and time scales of the physical phenomena are too large for microscopic (all atom) simulations. Alternative mesoscopic models based on a bead-spring description of polymer chains coupled to a hydrodynamic background, i.e., the Navier-Stokes equations for the solvent, allow to capture the basic physical principles but they are still computationally demanding. Therefore, macroscopic (two-fluid) models have been proposed in the literature which involve only averaged field quantities […]

Project G: Central soft matter simulation platform The goals of project G in the second funding phase of the TRR 146 have been the implementation of new methods of general interest into the molecular dynamics simulation environment ESPResSo++ Guzman et al. (2019), which can be used as foundation for research projects inside the TRR 146, and the optimization of ESPResSo++ to efficiently use modern HPC resources and therefore to become performance competitive with state-of-the-art MD environments like LAMMPS. Project G has been successful integrating new simulation methods by coupling ESPResSo++ with the ScaFaCos library Hofmann et al. (2018), Arnold et al. (2013) to provide fast parallelized long-range interaction algorithm (e.g. P3M / multipolar P3M), developing and implementing a new approach for Lees-Edwards boundary conditions to provide a fast parallel implementation of shear boundary conditions. The performance optimization of the ESPResSo++ environment included to change the memory layout to benefit from […]

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 […]