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The simulation of open molecular systems requires explicit or implicit reservoirs of energy and particles. Whereas full atomistic resolution is desired in the region of interest, there is some freedom in the implementation of the reservoirs. Here, we construct a combined, explicit reservoir by interfacing the atomistic region with regions of point-like, non-interacting particles (tracers) embedded in a thermodynamic mean field. The tracer molecules acquire atomistic resolution upon entering the atomistic region and equilibrate with this environment, while atomistic molecules become tracers governed by an effective mean-field potential after crossing the atomistic boundary. The approach is extensively tested on thermodynamic, structural, and dynamic properties of liquid water. Conceptual and numerical advantages of the procedure as well as new perspectives are highlighted and discussed., accepted as communication in Advanced Theory and Simulations

We investigate the role of the thermodynamic (TD) force, as an essential and sufficient technical ingredient for an efficient and accurate adaptive resolution algorithm. Such a force applied in the coupling region of an adaptive resolution Molecular Dynamics (MD) set-up, assures thermodynamic equilibrium between atomistically resolved and coarse-grained regions, allowing the proper exchange of molecules. We numerically prove that indeed for systems as relevant as liquid water and 1,3-dimethylimidazolium chloride ionic liquid, the combined action of the TD force and thermostat allows for computationally efficient and numerically accurate simulations, beyond the current capabilities of adaptive resolution set-ups, which employ switching functions in the coupling region., Accepted in Journal of Chemical Physics

We employ the Grand Canonical Adaptive Resolution Molecular Dynamics Technique (GC-AdResS) to test the spatial locality of the 1-ethyl 3-methyl imidazolium chloride liquid. In GC-AdResS atomistic details are kept only in an open sub-region of the system while the environment is treated at coarse-grained level, thus if spatial quantities calculated in such a sub-region agree with the equivalent quantities calculated in a full atomistic simulation then the atomistic degrees of freedom outside the sub-region play a negligible role. The size of the sub-region fixes the degree of spatial locality of a certain quantity. We show that even for sub-regions whose radius corresponds to the size of a few molecules, spatial properties are reasonably {reproduced} thus suggesting a higher degree of spatial locality, a hypothesis put forward also by other {researchers} and that seems to play an important role for the characterization of fundamental properties of a large class of ionic liquids., Comment: 25 pages, 18 figures

Zusammenfassung Für ausländische Studierende gehört es zur sprachlichen Studierfähigkeit, wissenschaftliche Texte in der Fremdsprache zu verfassen. Dabei kommt es häufig zu Schwierigkeiten, die nicht zuletzt mit dem Gebrauch von Quellen zusammenhängen: Viele Studierende sind unsicher, wie sie Quellen verwenden und dabei Plagiate vermeiden können. Hinzu kommt, dass die Übernahme von Sprachbausteinen eine geeignete Schreibstrategie darstellt, bei der allerdings die Grenze zum Plagiat leicht überschritten wird. Ausländische Studierende sehen sich daher häufig mit dem Vorwurf des Plagiats konfrontiert. Besonders bei Studierenden aus asiatischen Ländern wird zudem vermutet, dass es eine Kausalbeziehung gibt zwischen kultureller Prägung und der Übernahme fremder Formulierungen und/oder Inhalte ohne Verweis auf die Quelle. Der »Kultur-Plagiat-Hypothese« wurde auch in empirischen Untersuchungen nachgegangen. Eine Sichtung der Studien zur Kultur-Plagiat-Hypothese zeigt: Die methodischen Herausforderungen, auf die man bei Untersuchungen trifft, sind groß, die Ergebnisse uneinheitlich. Aus den Studien lassen sich dennoch interessante Beobachtungen gewinnen z. B. zum wissenschaftlichen Schreiben und zu Forschungsmethoden.

When integrating task-based learning into LSP courses, assessment procedures have to reflect the communicative goals of such tasks. However, performances on authentic and complex tasks are often difficult to score, because they involve not only specific language ability but also field specific knowledge. Moreover, the emphasis of tasks on meaning suggests that the communicative outcome should be regarded as the main criterion of success. This paper focuses on task design and scoring. It is argued that tasks have to be adapted to assessment purposes. However, to avoid a misalignment between teaching/learning and assessment, they should comprise the main features of LSP tasks in the sense of task-based language learning.

article i nfo In this paper a multiscale approach for the description of ionic liquids and first results according to this scheme are presented. The basic idea is to combine post-Hartree-Fock calculations (pHF), density functional theory (DFT) and classical all-atomistic molecular dynamics simulations to go from individual molecules to bulk properties in a setup that is able to bridge the large time and length scale gaps involved. The idea is initially applied to a very simple, but well studied ionic liquid compound, namely dimethylimidazolium chloride. Results obtained on the post-Hartree-Fock level for one ion pair are compared to Car-Parrinello density functional results. Subsequently density functional results for several ion pairs up to 30 ion pairs are determined, that are intended to approach bulk features. The DFT results are finally compared to molecular dynamics simulations. A crucial step in this multiscale scheme is the analysis of the electrostatic potentials. The Blochl approach employed herein on the DFT level allows us to obtain values for partial charges, that are considerably different from the ones used in the standard force fields. The results suggest that the total charge of the cation and the anion should be scaled down to a value of around ±0.6e to ±0.8e. The usage of these partial charges within a standard force field yields structural and dynamical results that approach the structural results of the density functional calculations. Although this appears promising, another refinement step of the force field parameters will be necessary, as the density of mass obtained deviates by 15% from the experimental results. Possible further refinements of the force fields are discussed.

Three different ionic liquids are investigated via atomistic molecular dynamics simulations using the force field of Lopes and PAdua (J. Phys. Chem. B 2006, 110, 19586). In particular, the 1-ethyl-3-methylimidazolium cation EMIM+ is studied in the presence of three different anions, namely, chloride Cl-, tetrafluoroborate BF(4)(-), and bis((trifluoromethyl)sulfonyly)imide TF2N-. In the focus of the present study are the static distributions of anions and cations around a cation as a function of anion size. It is found that the preferred positions of the anions change from being close to the imidazolium hydrogens to being above and below the imidazolium rings. Lifetimes of hydrogen bonds are calculated and found to be of the same order of magnitude as those of pure liquid water and of some small primary alcohols. Three kinds of short-range cation-cation orderings are studied, among which the offset stacking dominates in all of the investigated ionic liquids. The offset stacking becomes weaker from [EMIM][Cl] to [EMIM][BF4] to [EMIM][TF2N]. Further investigation of the dynamical behavior reveals that cations in [EMIM][TF2N] have a slower tumbling motion compared with those in [EMIM][Cl] and [EMIM][BF4] and that pure diffusive behavior can be observed after 1.5 ns for all three systems at temperatures 90 K above the corresponding melting temperatures.

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We present a detailed calculation of partial charges for the 1,3-dimethylimidazolium chloride ionic liquid. We first analyze MP2 electronic structure calculations and DFT results on isolated ion pairs with various methods of assigning partial charges to the atomic centers. In a second run we analyze the trajectory of a 25 ps long Car-Parrinello MD run of 30 ion pairs under bulk conditions using a charge fitting procedure due to Blöchl. Both, the single ion pair and the bulk system, provide us with a similar total ionic charge considerably less than unity. Especially the liquid state DFT results give convincing evidence for a reduced ionic charge on the ions. The similarity of both results suggest that the delocalization of the Cl charge is due only to local interactions. The relevance of our results is 2-fold; on the one hand they shed light on the basic property of the liquid and its reduced ionic character, and on the other hand, the ab initio derived partial charges provide a fundamental theoretical basis for the recent attempts to use the total ionic charge as an adjustable parameter. Furthermore, all our partial charges are subject to large fluctuations, hinting to the importance of polarization effects.

Local polarization effects, induced by monovalent and divalent positive ions in water, influence (and in turn are influenced by) the large-scale structural properties of the solvent. Experiments can only distinguish this process of interplay in a generic qualitative way. Instead, first-principles calculations can address the question at both the electronic and atomistic scale, accounting for electronic polarization as well as geometrical conformations. For this reason we study the extension of the scales' interconnection by means of first-principle Car?Parrinello molecular dynamics applied to systems of different size. In this way we identify the general aspects dominating the physics of the first solvation shell and their connection to the effects related to the formation of the outer shells and eventually the bulk. We show that while the influence of the ions is extended to the first shell only, the water?water interaction is instead playing a dominant role even within the first shell independently of the size or the charge of the ion.

We extend the use of the adaptive resolution method (AdResS) in its Grand Canonical-like version (GC-AdResS) to the molecular dynamics simulation of 1,3-dimethylimidazolium chloride. We show that the partitioning of the total system in a subsystem of interest with atomistic details and a reservoir of coarse-grained particles leads to satisfactory results. The challenging aspect of this study, compared to previous AdResS simulations, is the presence of charged particles and the necessity of addressing the question about the minimal physical input needed to model the coarse-grained particles in the reservoir. We propose two different approaches and show that in both cases they are sufficient to capture the decisive physical characteristics that allow a valid system-reservoir coupling. The technical satisfactory result paves the way for multiscale analysis of ionic liquids and for truly open boundary molecular simulations., Comment: published on: Phys. Chem. Chem. Phys., 2017,19, 4701-4709