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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

It is shown that the effect of substrate heating on the photo conversion efficiency in vacuum-deposited small molecule organic solar cells is closely related to the improved free charge generation in ordered C60 regions. The formation of these ordered regions strongly depends on the deposition sequence in the device and differs therefore between inverted and noninverted cells. Substrate-induced local fullerene ordering is found in small molecule:C60 bulk heterojunctions (BHJs) deposited on pristine C60 at elevated temperatures. This does not occur for BHJs deposited under identical conditions on pristine donor molecule layers, despite similar degrees of phase separation in both cases. These findings point to a hitherto unidentified advantage of inverted over noninverted solar cells that manifests itself in a higher charge separation efficiency.

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

It has been questioned whether students notice, act upon and, ultimately, learn from feedback if feedback about a task is received in conjunction with grades. If grades undermine feedback, it could be argued that it is a waste of teachers’ time to add comments to students’ written work if the students also receive grades. With reference to SLA (interactionist perspectives) and motivational psychology (achievement goal theory), we viewed the combination of grades and corrective feedback on L2 writing as a ‘multiple goal message’ and investigated its effect on performance.Three groups of adult learners of German took part in the experiment (N = 226). Participants produced three texts. Text 1 was written as a draft, text 2 was a revision of the draft and text 3 was an entirely new text on a different topic. The first group received corrective feedback (CF) on all texts (CF-only group), while the second group received grades in addition to the feedback (CF-and-grades group). The third group did not receive CF...

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.

This article investigates the effect of explicit individual corrective feedback (ICF) on L2 pronunciation at the micro-level in order to determine whether ICF needs to complement listening only interventions. To this purpose, the authors carried out a study which investigated the immediate effect of feedback on comprehensibility of controlled speech production by L2 learners. 169 adult learners of German were assigned to two groups, one exposed to listening only activities (listening to their own recorded pronunciation and listening to teachers' model pronunciation) and the other receiving ICF in addition to the listening activities. Immediately before and after the respective interventions, the participants read a text, and two experienced judges rated in a blind and randomized rating task whether they could determine differences between the comprehensibility of the pre-test and post-test samples. The results show that ICF was more effective than listening only interventions in improving L2 comprehensibility. The study thus concludes that ICF is a significantly more powerful teaching tool than listening only activities.

It is shown that chirality is common in bimetallic clusters. Specifically, a detailed computational study of two copper clusters, Cun+ (n = 9,11), demonstrates that exchange of one copper atom with another metal atom (Ni, Zn, Ag, or Au) at various locations, leads, in most cases, to chirality in the a priori achiral cluster (n = 9) and always preserves it in the a priori chiral one (n = 11). Chirality was evaluated on a quantitative level, employing the Continuous Chirality Measure methodology, in two versions: a purely geometric structure analysis, and an analysis which takes into account the different nature of the atoms. Physical aspects of chirality were demonstrated by emergence of vibrational circular dichroism signals and by the emergence of parity violation (PV) energy difference, which is calculated by employing a quasi-relativistic approach. In the case of AgCu10+(p9), the PV energy splitting value is about ∼10–15 Hartree, bringing this nanoalloy close to the range of systems that have been disc...

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.

It is generally assumed that second language (L2) learners find it difficult to self-assess their pronunciation skills. In view of the benefits of self-assessment for the language learning process and the need to monitor one’s pronunciation in independent learning environments, we investigated the reliability of self-assessments of pronunciation skills and set out to better understand the causes of difficulties. In our study, 46 advanced learners of German assessed their own articulation of different speech sounds in comparison with the sounds produced by a native speaker. In 85% of all cases the assessments of the raters and the self-assessments were identical. However, the learners only identified half of the number of speech sounds which the raters believed to be inaccurate. The study therefore confirms that even experienced L2 learners seem to find it difficult to self-assess correctly their pronunciation skills. In this paper we have explored a number of reasons for these difficulties in order to identify ways of further improving the self-assessment of L2 pronunciation.

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.

The organic cation and its interplay with the inorganic lattice underlie the exceptional optoelectronic properties of organo-metallic halide perovskites. Herein we report high-quality infrared spectroscopic measurements of methylammonium lead halide perovskite (CH3NH3Pb(I/Br/Cl)3) films and single crystals at room temperature, from which the dielectric function in the investigated spectral range is derived. Comparison with electronic structure calculations in vacuum of the free methylammonium cation allows for a detailed peak assignment. We analyze the shifts of the vibrational peak positions between the different halides and infer the extent of interaction between organic moiety and the surrounding inorganic cage. The positions of the NH3(+) stretching vibrations point to significant hydrogen bonding between the methylammonium and the halides for all three perovskites.

This study investigates the effect of background knowledge in languages for specific academic purposes (LSAP) tests. Following the observation of previous studies that the effect of background knowledge varies according to the level of language proficiency, the study applied the theory of linguistic thresholds to LSAP reading tests. The research question was whether students would be able to draw on their background knowledge only at certain levels of second language (L2) proficiency. International students in Germany took part in a study based on two LSAP reading tests from different subject areas. The texts were subject specific but did not assume previous knowledge. Language proficiency was assessed by C-tests; background knowledge by three different variables. The effect of background knowledge on reading test performance was strong. Whilst the effect of background knowledge did vary somewhat according to the level of language proficiency, the findings were inconclusive in relation to possible thresholds. In the case of the employed LSAP tests, which were not highly specific, they were fuzzy or non-existent and the concept seems inappropriate in relation to language tests for academic purposes.

Charge transfer (CT) mechanisms are crucial for device performance in organic electronics, but they are still not understood on a fundamental level. Here we want to show that in situ IR spectroscopy is very well suited to investigate CT effects in organic semiconductors in a qualitative and quantitative way. We study the ambipolar transport material 4,4´-bis(N-carbazolyl)-1,1´-biphenyl (CBP) as matrix and cesium carbonate (Cs2CO3) as n-dopant. To achieve doped layers, both materials were evaporated simultaneously. The system is one of the rare ones for n-doping of organic layers. In the spectra of the doped layers, additional absorption bands appear in the mid IR range. These can be assigned to the negatively charged matrix molecules that indicate electron transfer. The charged molecules exhibit these different absorption bands, as the charge transfer leads to a change in bond length and bond strength of the molecules. Our results very well agree with density functional theory calculations of the vibrational spectra of both, charged and non-charged molecules. By fitting the spectra of the doped layers as a superposition of the vibrational oscillators of neutral and charged species, we were able to quantify the amount of charged matrix molecules and to determine the doping efficiency of the investigated systems. For CBP n-doped with Cs2CO3 a hindrance of the CT due to air exposure could be observed.

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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.

The molecular polarization in a 1,3-dimethylimidazolium chloride ([DMIM][Cl]) ionic liquid is analyzed for a bulk liquid via the Car-Parrinello approach. The analysis reveals that the electric dipole moments of cations and anions are characterized by large fluctuations, however these are primarily due to the molecules in the immediate surroundings. These results on one hand shed light on some basic physical and chemical features of this liquid, and on the other represent a fundamental handle for the development of accurate classical force fields; this aspect is extensively discussed and some suggestions are made.

The influences of two different commonly employed force fields on statical and dynamical properties of ionic liquids are investigated for [EMIM][BF(4)]. The force fields compared in this work are the one of Canongia Lopes and Padua [J. Phys. Chem. B 110, 19586 (2006)] and that of Liu et al. [J. Phys. Chem. B 108, 12978 (2004)]. Differences in the strengths of hydrogen bonds are found, which are also reflected in the static ion distributions around the cation. Moreover, due to the stronger hydrogen bonding in the force field of Liu et al., the diffusive motions of cations and anions and the rotational behavior of the cations are slower compared with those obtained with the force field of Canongia Lopes and Padua. Both force fields underestimate the zero-field electrical conductivity, while the experimental dielectric constant can be reproduced within the expected statistical error boundaries.

The 1,3-dimethyl imidazolium chloride [MMIM]Cl is an example of ionic liquid and frequently studied in literature. In this article [MMIM]Cl is studied using an ab initio method [second order Moller-Plesset perturbation theory (MP2), density functional theory (DFT)] and classical force field approach with the aim of looking at some properties on different scales. Selected properties are studied with the different methods and compared to each other. The comparison between the results obtained with MP2 and the DFT approach allows us to comment on the validity of this latter and thus on its employment in larger systems. On the other hand, the comparison between the DFT results and those of the classical approach allows us to test the reproducibility of electrostatic properties by this latter approach. As the results show the used DFT setup is rather satisfactory, while the classical force fields are describing the electrostatic properties in an insufficient way. A revision (improvement) of the classical force fields is at this stage necessary in order to capture the electrostatic properties in a proper way.

It is commonly accepted that the water molecules in the first solvation shell of a positive ion are strongly polarized because of an elongation of the oxygen lone pair orbitals along the ion-oxygen direction and this is commonly considered the dominant effect. Recent experimental and theoretical works have instead suggested that this is not the dominant aspect and that the problem is by far more complicated. Consistent with the picture given above, here we show that, in particular, an equally important role into the polarization process is played by the bonding pair electrons located along the internal oxygen-hydrogen bond. We also provide some arguments which suggest that the main reason of such a behavior is due to the distortion of the molecular orbitals caused by the interaction between non-hydrogen-bonded water molecules in the first solvation shell of the ion.

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 performed first principles density functional calculations to study the effect of monovalent ions M+ (M = Li,Na,K) and A- (A = F,Cl,Br) in water with the aim of characterizing the local molecular properties of hydration. For this reason, several ion-water clusters, up to five or six water molecules were considered; such structures were optimized, and the Wannier analysis was then applied to determine the average molecular dipole moment of water. We found that with an increasing number of water molecules, the molecular polarization is determined by the water-water interaction rather than the water-ion interaction, as one would intuitively expect. These results are consistent with those obtained in previous density functional calculations and with other results obtained by employing classical polarizable water models. The main message of this work is that as one increases the number of molecules the average dipole moment of all water molecules and the ones in the first shell tends to the same value as the average of a similar sized cluster of pure water. This supports the use of nonpolarizable classical models of water in classical atomistic simulations.

Making use of the coupled cluster variant CCSD(T) and the aug-cc-pVQZ basis set a six-dimensional (6D) potential energy surface has been calculated for HCO2−, a fundamental organic anion. Therefrom, a variety of vibrational term energies and wavefunctions has been obtained by means of the discrete variable representation in an approach termed DVR(6). Calculated wavenumbers of the fundamentals of HCO2− and DCO2− agree with recent experimental values from neon matrix isolation IR spectroscopy within 15 cm−1. The out-of-plane bending vibrations v4 are predicted at 1030 and 894 cm−1. Moderately strong Fermi resonance interaction is calculated between vibrational states v1 and 2v4 of DCO2−. Excellent agreement with experiment (differences less than 0.7 cm−1) is observed for the 13C and 18O isotopic shifts. Accurate ground-state rotational constants are predicted for eight different isotopomers of the formate ion and the dissociation process HCO2− → H− + CO2 is investigated in some detail, with the dissociation energy D0 predicted to be 216 kJ mol−1.

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