Universität Stuttgart

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Author: search.filters.author.Hansen, NielsSubject: search.filters.subject.660

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    Predicting and rationalizing the Soret coefficient of binary Lennard‐Jones mixtures in the liquid state
    (2022) Zimmermann, Nils E. R.; Guevara‐Carrion, Gabriela; Vrabec, Jadran; Hansen, Niels
    The thermodiffusion behavior of binary Lennard‐Jones mixtures in the liquid state is investigated by combining the individual strengths of non‐equilibrium molecular dynamics (NEMD) and equilibrium molecular dynamics (EMD) simulations. On the one hand, boundary‐driven NEMD simulations are useful to quickly predict Soret coefficients because they are easy to set up and straightforward to analyze. However, careful interpolation is required because the mean temperature in the measurement region does not exactly reach the target temperature. On the other hand, EMD simulations attain the target temperature precisely and yield a multitude of properties that clarify the microscopic origins of Soret coefficient trends. An analysis of the Soret coefficient suggests a straightforward dependence on the thermodynamic properties, whereas its dependence on dynamic properties is far more complex. Furthermore, a limit of applicability of a popular theoretical model, which mainly relies on thermodynamic data, was identified by virtue of an uncertainty analysis in conjunction with efficient empirical Soret coefficient predictions, which rely on model parameters instead of simulation output. Finally, the present study underscores that a combination of predictive models and EMD and NEMD simulations is a powerful approach to shed light onto the thermodiffusion behavior of liquid mixtures.
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    An atomistic view on the uptake of aromatic compounds by cyclodextrin immobilized on mesoporous silica
    (2022) Kraus, Hamzeh; Hansen, Niels
    The effect of immobilized β-cyclodextrin (bCD) molecules inside a mesoporous silica support on the uptake of benzene and p -nitrophenol from aqueous solution was investigated using all-atom molecular dynamics (MD) simulations. The calculated adsorption isotherms are discussed with respect to the free energies of binding for a 1:1 complex of bCD and the aromatic guest molecule. The adsorption capacity of the bCD-containing material significantly exceeds the amount corresponding to a 1:1 binding scenario, in agreement with experimental observations. Beside the formation of 1:2 and, to a lesser extent, 1:3 host:guest complexes, also host-host interactions on the surface as well as more unspecific host-guest interactions govern the adsorption process. The demonstrated feasibility of classical all-atom MD simulations to calculate liquid phase adsorption isotherms paves the way to a molecular interpretation of experimental data that are too complex to be described by empirical models.