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 the first and second funding periods, we have made significant progress both in the development of methodologies for addressing dynamical consistency during model construction and also in gaining physical intuition into the time mappings of representative molecular liquids. We identified dynamical inconsistencies in a model azobenzene-based LC system (8AB8) that can be largely linked to the sampling of distinct translocation mechanisms in the smectic phase. We then developed methods to systematically identify and correct such deficiencies, by combining Markov-state-modelling techniques with traditional structure-based coarse-graining. We also performed detailed investigations into the dynamical properties of model imidazolium-based IL systems. We characterized time mappings for a range of CG models, and identified relationships between short and long times scale motions that can be used to construct dynamically-consistent CG models for ILs.

In the third funding period, we will merge our LC and IL activities and increase the structural and dynamical complexity of the studied systems to scrutinize and improve existing coarse-graining strategies and to approach situations closer to applications. By selecting “base” IL cations and anions and then making systematic chemical variations of these compounds via, e.g., changes in side chain length or polymerization of cations, we will strive for detailed insights into the relationship between molecular features and material properties. Explicitly, we will study IL-based LCs, polymerized ILs, and ILs mixed with small guest molecules. Common to all these systems is a prominent dynamical asymmetry, i.e., a coexistence of fast and slow constituents, which constitutes a serious challenge for CG models. In addition to equilibrium situations, we will consider non-equilibrium conditions. In particular, our goal is to develop efficient CG models of IL-based complex materials, which have predictive dynamical capabilities under shear flow. These methodical developments will pave the way for investigations of the role of their non-Newtonian nature under processing conditions.

Dynamical properties across different coarse-grained models for ionic liquids
Joseph F Rudzinski, Sebastian Kloth, Svenja Wörner, Tamisra Pal, Kurt Kremer, Tristan Bereau, Michael Vogel
Journal of Physics: Condensed Matter 33 (22), 224001 (2021)
see publication

Coarse-grained model of a nanoscale-segregated ionic liquid for simulations of low-temperature structure and dynamics
Joseph F. Rudzinski and Tristan Bereau
Journal of Chemical Physics 153, 214110 (2020)
see publication

Direct route to reproducing pair distribution functions with coarse-grained models via transformed atomistic cross correlations
Svenja J. Wörner, Tristan Bereau, Kurt Kremer, Joseph F. Rudzinski
The Journal of Chemical Physics 151 (24), 244110 (2019)
see publication

Automated detection of many-particle solvation states for accurate characterizations of diffusion kinetics
Joseph F. Rudzinski, Marc Radu, Tristan Bereau
The Journal of Chemical Physics 150 (2), 024102 (2019)
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On the relevance of electrostatic interactions for the structural relaxation of ionic liquids: A molecular dynamics simulation study
Tamisra Pal, Michael Vogel
The Journal of Chemical Physics 150 (12), 124501 (2019)
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Accurate Structure-Based Coarse Graining Leads to Consistent Barrier-Crossing Dynamics
Tristan Bereau, Joseph F. Rudzinski
Physical Review Letters 121 (25), (2018)
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Effects of Silica Surfaces on the Structure and Dynamics of Room-Temperature Ionic Liquids: A Molecular Dynamics Simulation Study
Tamisra Pal, Constantin Beck, Dominik Lessnich, Michael Vogel
The Journal of Physical Chemistry C122 (1), 624-634 (2017)
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Single molecule translocation in smectics illustrates the challenge for time-mapping in simulations on multiple scales
Biswaroop Mukherjee, Christine Peter, Kurt Kremer
The Journal of Chemical Physics 147 (11), 114501 (2017)
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Role of Dynamic Heterogeneities in Ionic Liquids: Insights from All-Atom and Coarse-Grained Molecular Dynamics Simulation Studies
Tamisra Pal, Michael Vogel
ChemPhysChem 18 (16), 2233-2242 (2017)
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Computational materials discovery in soft matter
T. Bereau, D. Andrienko, K. Kremer
APL Materials 4, 053101 (2016)
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Concurrent parametrization against static and kinetic information leads to more robust coarse-grained force fields
J.F. Rudzinski, T. Bereau
The European Physical Journal Special Topics 225 (8-9), 1373-1389 (2016)
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Communication: Consistent interpretation of molecular simulation kinetics using Markov state models biased with external information
Joseph F. Rudzinski, Kurt Kremer, Tristan Bereau
The Journal of Chemical Physics 144 (5), 051102 (2016)
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A molecular dynamics simulations study on the relations between dynamical heterogeneity, structural relaxation, and self-diffusion in viscous liquids
Patrick Henritzi, André Bormuth, Felix Klameth, Michael Vogel
The Journal of Chemical Physics 143 (16), 164502 (2015)
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