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Deep eutectic solvents as sustainable and new-generation solvents show potential in the field of cellulose dissolution. Although these novel materials are tested for numerous industrial, environmental, and medical applications, little is known about the structural features of cellulose interacting with deep eutectic solvents. In this work, the interplay of cellulose is studied in two deep eutectic solvents: choline acetate mixed with urea and choline chloride mixed with urea using classical molecular dynamics simulations. Dissolution of cellulose in the studied liquids was not observed to be in agreement with experimental work from the literature. However, a slight swelling in the chloride, as compared to the acetate-based solvent, is apparent. A possible rationale might be found in the stronger hydrogen bonding of the chloride anion compared to the acetate anion with the hydrogen atoms of the cellulose. Moreover, chloride approaches the outer glucose units comparatively more, which could be interpreted as the onset of entering and thus dissolving the cellulose as was previously observed. Specific hydrogen bonds between all units are analyzed and discussed in detail. [ABSTRACT FROM AUTHOR]

Chirality transfer from the chiral molecule (R)‐1,2‐propylene oxide to the achiral anion of the 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid is observed. The chiral probe selectively affects one part of the binary ionic liquid, i. e., it has previously been shown experimentally and theoretically that this particular imidazolium cation can be affected by chirality transfer, but in the present system chirality is almost exclusively transferred to the anion and not to both parts of the solvent (anion and cation). This observation is of high relevance because of its selectivity and because anion effects are usually much more important in ionic liquid research than cation effects. From ab initio molecular dynamics simulations, a conformational analysis and dissected vibrational circular dichroism spectra are obtained to study the chirality transfer. While in the neat ionic liquid two mirror imaged trans conformers of the anion occur almost equally, we observe an excess of one of these conformers in the presence of the chiral solute, causing optical activity of the anion. Although the cis conformers are not tremendously affected by the chirality transfer, they gain in total population when (R)‐1,2‐propylene oxide is dissolved in the ionic liquid. [ABSTRACT FROM AUTHOR]

Deep eutectic solvents show great potential as CO2 absorbents, which is highly desirable for the sustainable development of CO2 reduction and prevention of global climate changes. Ab initio molecular dynamics simulations in the isothermal–isobaric ensemble at pressures of 1 MPa and 5 MPa and at the corresponding experimental density are carried out to investigate the CO2 absorption in choline chloride: ethylene glycol deep eutectic solvent. Based on the structural analysis, there is a strong anion and hydrogen bond donor effect and a minor cation effect on CO2 solvation in the solvent. Instead of cooperation, a competition between the anion and the hydrogen bond donor (ethylene glycol) for the interaction with CO2 is indicated. While at a lower pressure, the ethylene glycol–CO2 interaction dominates, at a higher pressure, it is the chloride–CO2 interaction. Thus, it is possible to use the same advantages within the deep eutectic solvent as the CO2 absorbent as in ionic liquids, but in the hydrogen bond, a donor can be exploited. [ABSTRACT FROM AUTHOR]

Ionic liquids raise interesting but complicated questions for theoretical investigations due to the fact that a number of different inter-molecular interactions, e.g., hydrogen bonding, long-range Coulomb interactions, and dispersion interactions, need to be described properly. Here, we present a detailed study on the ionic liquids ethylammonium nitrate and 1-ethyl-3-methylimidazolium acetate, in which we compare different dispersion corrected density functional approximations to accurate local coupled cluster data in static calculations on ionic liquid clusters. The efficient new composite method B97-3c is tested and has been implemented in CP2K for future studies. Furthermore, tight-binding based approaches which may be used in large scale simulations are assessed. Subsequently, ab initio as well as classical molecular dynamics simulations are conducted and structural analyses are presented in order to shed light on the different short- and long-range structural patterns depending on the method and the system size considered in the simulation. Our results indicate the presence of strong hydrogen bonds in ionic liquids as well as the aggregation of alkyl side chains due to dispersion interactions. [ABSTRACT FROM AUTHOR]

In this study, we aim at understanding the influence of dispersion correction on the ab initio molecular dynamics simulations of ionic liquid (IL) systems. We investigated a large bulk system of the 1-butyl-3-methylimidazolium triflate IL and a small cluster system of ethylamine in ethylammonium nitrate both under periodic boundary conditions. The large system displays several changes upon neglect of dispersion correction, the most striking one is the surprising decrease of the well-known microheterogeneity which is accompanied by an increase of side chain hydrogen atom-anion interplay. For the diffusion coefficient, we observe a correction towards experimental behavior in terms of the cation becoming faster than the anion with dispersion correction. Changes in the electronic structure upon dispersion correction are reflected in larger/smaller dipole moments for anions/cations also seen in the calculated IR spectrum. The energetics of different ion pair dimer subsystems (polar and non-polar) are in accordance with the analysis of the trajectories: A detailed balance in the ionic liquid system determines its particular behavior. While the overall interaction terms for dispersion-corrected calculations are higher, the decrease in microheterogeneity upon inclusion of dispersion interaction becomes obvious due to the relation between all contributions to polar-polar terms. For the small system, we clearly observe the well known behavior that the hybrid functionals show higher reaction barriers than the pure generalized gradient approximation (GGA) functionals. The correction of dispersion reduces the discrepancies in some cases. Accounting for the number of jumps, we observe that dispersion correction reduces the discrepancies from 50% to less than 10%. [ABSTRACT FROM AUTHOR]

The scaling behavior of ab initio molecular dynamics simulations for the different size bulk systems of liquid methanol is presented and thereby the characteristics of every system performing on either a local compute cluster or a supercomputer are analyzed. Additionally, the influence of different parameters on the quality of the infrared and Raman spectra is investigated using different simulation frameworks, including time step, convergence criteria, density functional approximation, and basis set. Both the maximally localized Wannier functions and the radical Voronoi tessellation approaches are employed to evaluate vibrational spectra from the trajectories. The results of infrared and Raman spectra are classified in two frequency regions, 500 to 1600 cm−1 and 2500 to 4000 cm−1, in order to compare and discuss the experimental spectra and the results derived from ab initio molecular dynamics simulations comprehensively. The outcome of this study guides future experimental and theoretical researchers in order to acquire a profound perception into vibrational spectra, which evolves the way of elucidating molecular structure. [ABSTRACT FROM AUTHOR]

The large electrochemical and cycling stability of "water‐in‐salt" systems have rendered promising prospective electrolytes for batteries. The impact of addition of water on the properties of ionic liquids has already been addressed in several publications. In this contribution, we focus on the changes in the state of water. Therefore, we investigated the protic ionic liquid N‐butyl‐pyrrolidinium bis(trifluoromethanesulfonyl)imide with varying water content at different temperatures with the aid of molecular dynamics simulations. It is revealed that at very low concentrations, the water is well dispersed and best characterized as shared solvent molecules. At higher concentrations, the water forms larger aggregates and is increasingly approaching a bulk‐like state. While the librational and rotational dynamics of the water molecules become faster with increasing concentration, the translational dynamics are found to become slower. Further, all dynamics are found to be faster if the temperature increases. The trends of these findings are well in line with the experimental measured conductivities. [ABSTRACT FROM AUTHOR]

The vibrational spectra of the ionic liquid 1-ethyl-3-methylimidazolium acetate and its mixtures with water and carbon dioxide are calculated using ab initio molecular dynamics simulations, and the results are compared to experimental data. The new implementation of a normal coordinate analysis in the trajectory analyzer TRAVIS is used to assign the experimentally observed bands to specific molecular vibrations. The applied computational approaches prove to be particularly suitable for the modeling of bulk phase effects on vibrational spectra, which are highly important for the discussion of the microscopic structure in systems with a strong dynamic network of intermolecular interactions, such as ionic liquids. [ABSTRACT FROM AUTHOR]

By means of classical molecular dynamics simulation the interfacial properties of methanol and n‐dodecane, which are two potential candidate solvents for use in non‐aqueous liquid–liquid extraction, were assessed. The question of how the interface changes depending on the concentration of extractant (tri‐n‐butyl phosphate) and salt (LiCl) is addressed. Two different models to represent systems were used to evaluate how LiCl and tri‐n‐butyl phosphate affect mutual miscibility, and how the last‐named behaves depending on the chemical environment. Tri‐n‐butyl phosphate increases the mutual solubility of the solvents, whereas LiCl counteracts it. The extractant was found to be mostly adsorbed on the interface between the solvents, and therefore the structural features of the adsorption were investigated. Adsorption of tri‐n‐butyl phosphate changes depending on its concentration and the presence of LiCl. It exhibits a preferential orientation in which the butyl chains point at the n‐dodecane phase and the phosphate group points at the methanol phase. For high concentrations of tri‐n‐butyl phosphate, its molecular orientation is preserved by diffusion of the excess molecules into both the methanol and n‐dodecane phases. However, LiCl hinders the diffusion into the methanol phase, and thus increases the concentration of tri‐n‐butyl phosphate at the interface and forces a rearrangement with subsequent loss of orientation. [ABSTRACT FROM AUTHOR]

We present a comprehensive molecular dynamics simulation study on 1-butyl-3-methylimidazolium ionic liquids and their fluorinated analogs. The work focused on the effect of fluorination at varying anions. The main findings are that the fluorination of the cations side chain increases overall structuring, especially the aggregation of cation side chain. Furthermore, large and weakly coordinating anions tend to occupy on-top positions of the cation and decrease the aggregation of cation side chains, most likely due to enhanced alkyl-anion interaction. [ABSTRACT FROM AUTHOR]

The dynamics of the protic ionic liquid monomethylammonium nitrate is investigated by Car–Parrinello molecular dynamics simulations. On average, 1.8 of 3 possible hydrogen bond contacts are formed. Therefore, one hydrogen bond acceptor and one donor site in each ion pair of monomethylammonium nitrate remains free, which is similar to water. Furthermore, like water, monomethylammonium nitrate exhibits a fast fluctuating hydrogen bond network. The comparable hydrogen bond network and dynamics of both liquids might explain the similar impact on reactivity and selectivity found for chemical reactions. However, the hydrogen bond network of monomethylammonium nitrate and water show some structural differences. While the hydrogen bonds in water arrange in parallel fashion, the hydrogen bonds of monomethylammonium nitrate prefer angles of 0°, 90°, and 180°. The ion dynamics of monomethylammonium nitrate indicate that at about 85% of the ion pairs are still connected after 14.5 ps. A closer inspection of the first solvation shell dynamics of one cation reveals that after 11 ps the current ion pair conformation is independent of the initial ion pair conformation because the ion pairs lose their information of the initial ion pair conformation much faster than the time needed to escape from their solvent cage. The ion dynamics of monomethylammonium nitrate can be described by the following model: There are ions rattling in long living cages which are formed by long living ion pairs. [ABSTRACT FROM AUTHOR]

The scalar-relativistic Douglas–Kroll–Hess method is implemented in the Born–Oppenheimer molecular dynamics simulation package CP2K. Using relativistic densities in a nonrelativistic gradient routine is found to be a valid approximation of relativistic gradients. An excellent agreement between optimized structures and geometries obtained from numerical gradients is observed with an error smaller than 0.02 pm. Hydrogen halide dimers [(HX)2, with X=F, Cl, Br, I] serve as small test systems for first-principles molecular dynamics simulations. Relativistic effects are observed. That is, the amplitude of motion is larger, the frequency of motion is smaller, and the distances are larger in the relativistic picture. Several localization schemes are evaluated for different interatomic and intermolecular distances. The errors of these localization schemes are small for geometries which are similar to the equilibrium structure. They become larger for smaller distances, introducing a slight bias toward closed packed configurations. [ABSTRACT FROM AUTHOR]

In the present study, we employ quantum cluster equilibrium calculations on a small water cluster set in order to derive thermochemical equilibrium properties of the liquid phase as well as the liquid-vapor phase transition. The focus is set on the calculation of liquid phase entropies, from which entropies of vaporization at the normal boiling point of water are derived. Different electronic structure methods are compared and the influences of basis set size and of cooperative effects are discussed. In line with a previous study on the subject [B. Kirchner, J. Chem. Phys. 123, 204116 (2005)], we find that the neglect of cooperativity leads to large errors in the equilibrium cluster populations as well as in the obtained entropy values. In contrast, a correct treatment of the intermolecular many-body interaction yields liquid phase entropies and phase transition entropies being in very good agreement with the experimental reference, thus demonstrating that the quantum cluster equilibrium partition function intrinsically accounts for the shortcomings of the ideal gas partition function often employed in first principles entropy calculations. Comparing the calculated vaporization entropies to the value predicted by Trouton’s rule, it is observed that for entropy calculations the consideration of intracluster cooperative effects is more important than the explicit treatment of the intercluster association even in a highly associated liquid such as water. The decomposition of entropy into contributions due to different degrees of freedom implies the need for the accurate treatment of particle indistinguishability and free volume of translation, whereas minor influences should be expected from the vibrational and rotational degrees of freedom and none from the electronic degrees of freedom. [ABSTRACT FROM AUTHOR]

We present an efficient implementation for the calculation of maximally localized Wannier functions (MLWFs) during parallel Car-Parrinello molecular dynamics simulations. The implementation is based on a block Jacobi method. The calculation of MLWFs results in only a moderate (10%–20%) increase in computer time. Consequently it is possible to calculate MLWFs routinely during Car-Parrinello simulations. The Wannier functions are then applied to derive molecular dipole moments of dimethyl sulfoxide (DMSO) in gas phase and aqueous solution. We observe a large increase of the local dipole moment from 3.97 to 7.39 D. This large solvent effect is caused by strong hydrogen bonding at the DMSO oxygen atom and methyl groups. Decomposing the dipole moment into local contributions from the S-O bond and the methyl groups is used to understand the electrostatic response of DMSO in aqueous solution. A scheme is given to derive charges on individual atoms from the MLWFs using the D-RESP methodology. The charges also display large solvent effects and give insight into the transferability of recent force field models for DMSO. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this work, the properties of "water‐in‐PIL" (PIL=protic ionic liquid) electrolytes are reported based on 1‐butylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PyrH4TFSI). Taking advantage of experimental and theoretical investigations, it is shown that the amount of water inside the electrolyte has a dramatic effect on the viscosity, conductivity, density, cation–anion interplay, and electrochemical stability of PyrH4TFSI. The impact of water on the properties of this ionic liquid also affects its use as an electrolyte for electrochemical double‐layer capacitors (EDLCs). It is shown that the presence of water improves the transport properties of PyrH4TFSI, with a beneficial effect on the capacitance retention of the devices in which these electrolytes are used. However, at the same time, water reduces the operative voltage of EDLCs containing this PIL as the electrolyte and, furthermore, it has a strong impact on the inactive components of these systems. To suppress this latter problem, and to realize EDLCs with high stability, the use of inactive components stable in aqueous environment appears necessary. [ABSTRACT FROM AUTHOR]

Hydrogen is often regarded as fuel of the future, and there is an increasing demand for the development of anhydrous proton-conducting electrolytes to enable fuel-cell operation at elevated temperatures exceeding 120°C. Much attention has been directed at protic ionic liquids as promising candidates, but in the search for highly conductive systems the possibility of designing Grotthuss diffusion-enabled protic ionic liquids has been widely overlooked. Herein, the mechanics of protontransfer mechanism in the equimolar mixture of N-methylimidazole and acetic acid was explored using ab initio molecular dynamics simulations. The ionicity of the system is approximated with good agreement to experiments. This system consists mostly of neutral species but exhibits a high ionic conductivity through Grotthuss-like proton conduction. Chains of aceticacid molecules and other species participating in the protontransfer mechanisms resembling Grotthuss diffusion could be directly observed. Furthermore, based on these findings, a series of static quantum chemical calculations was conducted to investigate the effect of substituting the anion and cation with different functional groups. We predict whether a given combination of cation and anion will be a true ionic liquid or a molecular mixture and propose some systems as candidates for Grotthuss diffusion-enabled protic ionic liquids. [ABSTRACT FROM AUTHOR]

Material synthesis in ionic liquids, at or near room temperature, is currently a subject of immense academic interest. In order to illuminate molecular-level details and the underlying chemistry, we carried out molecular simulations of a single Te4Br2 molecule dissolved in the ionic liquid 1-ethyl-3-methylimidazolium chloride, as well as in the ionic liquid mixed with aluminum chloride. Although the ethyl side chain is much too short to show detailed microheterogeneity, significant structuring with the small chloride anions is seen in case of the pure ionic liquid. In the case of the mixture, formation of larger anionic clusters is distinctly observed and analyzed. Due to the tendency of ionic liquids to dissociate, there is a pronounced shift to elongated Te-Br distances in both investigated solvents. However, only in the AlCl3-containing liquid, we observe the reaction of the open chain-like Te4Br2 molecule to a closed square-like Te4Br+ and AlCl3Br- ion. The molecular arrangement of the [Te4]2+ unit shows negligible deviation from that in the experimental crystal structure. [ABSTRACT FROM AUTHOR]

We carried out ab initio molecular dynamics simulations for the three cyano-based ionic liquids, 1-ethyl-3-methylimidazolium tetracyanoborate ([C2C1Im][B(CN)4]), 1-ethyl-3-methyl-imidazolium dicyanamide ([C2C1Im][N(CN)2]), and 1-ethyl-3-methylimidazolium thiocyanate ([C2C1Im][SCN]). We found that the [SCN]-based ionic liquid is much more prone to π-π stacking interactions as opposed to the other two ionic liquids, contrary to the fact that all liquids bear the same cation. Hydrogen bonding is strong in the dicyanamide- and the thiocyanate-based ionic liquids and it is almost absent in the tetracyanoborate liquid. The anion prefers to stay on-top of the imidazolium ring with the highest priority for the [N(CN)2]- anion followed by the [B(CN)4]- anion. We find that experimental viscosity trends cannot be correlated to the hydrogen bond dynamics which is fastest for [B(CN)4]- followed by [SCN]- and [N(CN)2]-. For the dynamics of the cation on-top of itself, we find the order of [B(CN)4]- followed by [N(CN)2]- and finally by [SCN]-. Interestingly, this trend correlates well with the viscosity, suggesting a relation between the cation-cation dynamics and the viscosity at least for these cyano-based ionic liquids. These findings, especially the apparent correlation between cation-cation dynamics and the viscosity, might be useful for the suggestion of better ionic liquids in electrolyte applications. [ABSTRACT FROM AUTHOR]

An increasing lack of single ion cation-anion associations (ion pairing) in ionic liquids suggests a structural motif that stands in contradiction to the single ion pair structure of their vapor phase, which was evidenced by different experimental and theoretical studies. Therefore, a structural rearrangement has to occur en route from the liquid to the vapor. In this study, we propose a detailed four-step evaporation mechanism for ionic liquids, providing a refined perspective on the theory of this process based on the connection between ion pairing and volatility. The process involves diffusion of ions from the bulk to the surface, where they float around until a well-defined ion pair is formed with a counterion, leading to the departure from the surface into the vacuum. To assess the validity of this scheme, we performed a series of classical and ab initio molecular dynamics simulations based on the most sophisticated methods and force fields available for ionic liquids. [ABSTRACT FROM AUTHOR]

We have carried out an ab initio molecular dynamics study on the sulfur dioxide (SO) solvation in 1-ethyl-3-methylimidazolium thiocyanate for which we have observed that both cations and anions play an essential role in the solvation of SO. Whereas, the anions tend to form a thiocyanate- and much less often an isothiocyanate-SO adduct, the cations create a 'cage' around SO with those groups of atoms that donate weak interactions like the alkyl hydrogen atoms as well as the heavy atoms of the $$\pi $$ -system. Despite these similarities between the solvation of SO and CO in ionic liquids, an essential difference was observed with respect to the acidic protons. Whereas CO avoids accepting hydrogen bonds form the acidic hydrogen atoms of the cations, SO can from O(SO)-H(cation) hydrogen bonds and thus together with the strong anion-adduct it actively integrates in the hydrogen bond network of this particular ionic liquid. The fact that SO acts in this way was termed a linker effect by us, because the SO can be situated between cation and anion operating as a linker between them. The particular contacts are the H(cation) $$\cdots $$ O(SO) hydrogen bond and a S(anion)-S(SO) sulfur bridge. Clearly, this observation provides a possible explanation for the question of why the SO solubility in these ionic liquids is so high. [ABSTRACT FROM AUTHOR]

Ionic liquids-which are special solvents composed entirely of ions-are difficult albeit interesting to study for several reasons. Owing to the many possible cation and anion combinations that form ionic liquids, common properties are hard to classify for them, which makes the theoretical investigation crucial for ionic liquids. The system size, the amount of possible isomers including cation-anion orientation and coordination, as well as the rotation of the side chain(s) prevent the use of high-level electronic structure methods, and density functional theory is the method of choice. Dispersion forces-although they are small compared to electrostatics-play a major role in ionic liquids; therefore, methods that describe such kind of interplay are preferred. Between the cation and the anion, there is a sizable charge transfer, which has important consequences for molecular dynamics simulations and force field development. Already based on the first generation of force fields important discoveries were made, namely that ionic liquids are nanostructured. Moreover, it was possible to predict that their distillation is possible. Throughout the construction of these force fields, transferability was taken into account which allowed them to describe homologous series. For studying reactions in ionic liquid ( IL) media, continuum models were found to improve the results. Ab initio molecular dynamics ( AIMD) and quantum mechanics ( QM)/molecular mechanics ( MM) approaches are well suited for spontaneous events. In case of very large systems, such as cellulose in ionic liquids, coarse-grained methods are providing insight and are applied more frequently. This makes ionic liquids real multiscalar systems. WIREs Comput Mol Sci 2015, 5:202-214. doi: 10.1002/wcms.1212 Conflict of interest: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the . [ABSTRACT FROM AUTHOR]

In the reaction of 1-ethyl-3-methylimidazolium acetate [C2C1Im][OAc] ionic liquid with carbon dioxide at 125 °C and 10 MPa, not only the known N-heterocyclic carbene (NHC)-CO2 adduct I, but also isomeric aNHC-CO2 adducts II and III were obtained. The abnormal NHC-CO2 adducts are stabilized by the presence of the polarizing basic acetate anion, according to static DFT calculations and ab initio molecular dynamics studies. A further possible reaction pathway is facilitated by the high basicity of the system, deprotonating the initially formed NHC-CO2 adduct I, which can then be converted in the presence of the excess of CO2 to the more stable 2-deprotonated anionic abnormal NHC-CO2 adduct via the anionic imidazolium-2,4-dicarboxylate according to DFT calculations on model compounds. This suggests a generalizable pathway to abnormal NHC complex formation. [ABSTRACT FROM AUTHOR]

The solvation of the carbene 1-ethyl-3-methylimidazole-2-ylidene in the ionic liquid 1-ethyl-3-methylimidazolium acetate was investigated by ab initio molecular dynamics simulations in order to reveal the interaction between these two highly important classes of materials: N-heterocyclic carbenes with superb catalytic activity and ionic liquids with advantageous properties as solvents and reaction media. In contrast to previously published data on analogous systems, no hydrogen bond is observed between the hypovalent carbon atom and the most acidic ring hydrogen atoms, as these interaction sites of the imidazolium ring are predominantly occupied by the acetate ions. Keeping the carbene away from the ring hydrogen atoms prevents stabilization of this reactive species, and hence any retarding effect on subsequent reactions, which explains the observed high reactivity of the carbene in acetate-based ionic liquids. Instead, the carbene exhibits a weaker interaction with the methyl group of the imidazolium cation by forming a hitherto unprecedented kind of C⋅⋅⋅HC hydrogen bond. This unexpected finding not only indicates a novel kind of hydrogen bond for carbenes, but also shows that such interaction sites of the imidazolium cation are not limited to the ring hydrogen atoms. Thus, the results give the solute-solvent interactions within ionic liquids a new perspective, and provide a further, albeit weak, site of interaction to tune in order to achieve the desired environment for any dissolved active ingredient. [ABSTRACT FROM AUTHOR]

We present Car-Parrinello molecular dynamics simulations of the liquid imidazolium chloride/AlCl3 by inserting one pair of [C2C1im]Cl into liquid AICI3, forming an acidic mixture. Two different starting conditions lead to two trajectories from which we harvest structural data. For both simulations, we find large anions within the equilibrium phase: In both trajectories at longer simulation time, the anion size converges to four monomer units, i.e., to Al4Cl13-. The cluster size fluctuations indicate that Grotthus diffusion must play a role. We discuss one possible mechanism of such a reaction changing the anionic species. This process involves many steps of chlorine rattling, bond breaking, and bond forming. With the aid of the electron localization function, a probable rationale for the formation of larger anions is determined: Large anionic species are formed simply to account for the "lack of electrons" present in the acidic melt. [ABSTRACT FROM AUTHOR]

Abstract: It is the aim of this work to elucidate the usefulness and feasibility of the first-principles approach and to extend it to the regime of liquid molecular substances of complex structure. Physical and thermodynamic properties of complicated liquids are investigated by means of Car–Parrinello molecular dynamics (CPMD) and also with static quantum chemical methods. The connection between the dynamic and static approach is given by the quantum cluster equilibrium (QCE) theory. Since the QCE theory is not yet well established, a new implementation in the MD post-processing program PEACEMAKER is presented. It can be shown that it is by far more important to include cooperative effects rather than to concentrate the effort on the inclusion of weak dispersion forces not present in current density functionals. Traditionally, investigations of complicated liquids were also undertaken with the tools of simple liquids, because for some problems the size of the system does not allow for a more accurate description. Although linear-scaling techniques are simplifications from the point of view of quantum chemistry, they might be severe improvements when compared to traditional molecular dynamics simulations. For the interpretation of the liquid state the introduction of local properties is inevitable. New methods are presented for the calculation of local dipole moments and for the estimation of hydrogen bond energies in quantum mechanically nondecomposable systems. The latter also allows for the detection of hydrogen bonds in simulations through a wavefunction-based criterion instead of one which is solely grounded on the geometric structure of the atomic nuclei involved. The article then discusses prominent liquids which show properties that are not yet understood. Another part of the work analyzes the effect of solvent molecules on solutes and their reactions in the solvent. Finaly, neoteric solvents, such as ionic liquids are discussed. [Copyright &y& Elsevier]

Abstract: We introduce a density functional based embedding method for the study of molecular systems in condensed phase. Molecular subunits are treated using a standard Kohn–Sham method together with an embedding potential derived from orbital-free density functional theory, by using kinetic energy functionals. The method leads to a linear scaling electronic structure approach that maps naturally onto massively parallel computers. The application of the method for a molecular dynamics simulation of water at ambient conditions results in a liquid with unstructured second solvation shell. [Copyright &y& Elsevier]

Molecular dynamics simulations are performed with ab initio calculated potentials and electric field gradient curves on different levels of approximation, to study their influence on the relaxation time and diffusion coefficient of fluid 21Ne. Additional properties, such as quadrupole couplings, effective electric field gradient correlation times, and diffusion correlation times, are studied to get a better understanding of the underlying mechanisms. Semiquantitative models for the total, self and cross correlation functions of the electric field gradient are developed. [ABSTRACT FROM AUTHOR]

To gain a deeper understanding of the TiCl 4 solvation effects in multi-component ionic liquids, we performed ab initio molecular dynamics simulations of 1-butyl-3-methylimidazolium [C 4 C 1 Im] + , tetrafluoroborate [BF 4 ] − , chloride [Cl] − both with and without water and titanium tetrachloride TiCl 4 . Complex interactions between cations and anions are observed in all investigated systems. By further addition of water and TiCl 4 this complex interaction network is extended. Observations of the radial distribution functions and number integrals show that water and TiCl 4 not only compete with each other to interact mainly with [Cl] − , which strongly influences the cation-[BF 4 ] − interaction, but also interact with each other, which leads to the fact that in certain systems the cation-anion interaction is enhanced. Further investigations of the Voronoi polyhedra analysis have demonstrated that water has a greater impact on the nanosegregated system than TiCl 4 which is also due to the fact of the shear amount of water relative to all other components and its higher mobility compared to TiCl 4 . Overall, the polar network of the IL mixture collapses by including water and TiCl 4 . In the case of [Cl] − chloride enters the water continuum, while [BF 4 ] − remains largely unaffected, which deeply affects the interaction of the ionic liquid (IL) network. [ABSTRACT FROM AUTHOR]

[Display omitted] • Stilbazolium chromophores and small to medium-size anions form aggregates. • The methylpyridinium group of the cations is the most interactive region for the self-aggregation. • These aggregates adopt a preferential Λ-shape with contributions from head-to-head and stacked forms. • Classical molecular dynamics simulation is a reliable tool to evaluate the aggregation constants for non-symmetric aggregates. Molecular aggregation plays an important role on optical phenomena, and optimizing the latter requires understanding the aggregation behavior as a function of the molecular structures. The formation of molecular aggregates composed of stilbazolium chromophores and small to medium-size anions is studied by carrying out classical molecular dynamics (MD) simulations, shedding light on the dynamics of spontaneous self-aggregation of anion-cation (AC) pairs and estimating their equilibrium aggregation constants. First, analyses based on atom-atom distances and on contact mapping (Voronoi tessellation) highlight that the interactions occur at the level of the methylpyridinium groups of the cations, which enabled monitoring the clustering dynamics. Then, simulations show that clusters containing up to 5 AC pairs dominate the populations. Among the AC pairs, two of them (where the stilbazolium bears a strong donor substituent and when the anion is SCN- or pTS-) aggregate into small clusters even at high concentration, corroborating related experimental results [ChemPhysChem. 11 (2010) 495–507]. Still, these MD simulations do not reveal strict relationships between the aggregate size and the nature of the anion. Nevertheless, AC pairs bearing iodide anions require longer MD simulation times to reach an asymptotic equilibrium tendency of the average number of clusters. Finally, the aggregates are shown to adopt a preferential Λ-shape with contributions from head-to-head and stacked forms. Complementarily, the analyses of the isoperimetric quotient reinforce the AC pairs are not forming spherical aggregates even for clusters including more than 10 AC pairs. So, when the stilbazolium bears a strong donor substituent and when the anion is pTS-, stacked aggregates are formed, at both low and high concentrations, resulting in excellent agreement with the measured aggregation equilibrium constant. [ABSTRACT FROM AUTHOR]

• The simulated Fe-rich slag structure fits well with the experimental data. • Fe is predominately 4- and 5-fold coordinated with O. • The [FeO 4 ] units are connected by sharing corners while the [FeO 5 ] polyhedra share edges. • Fe and Ca seem to be randomly distributed throughout the silicate network. Non-ferrous metallurgy slags are gaining significant interest as a resource in the production of alternative low-energy cementitious materials. Their atomistic structures, however, are still not fully understood due to their glassy nature. In the work presented herein, a comprehensive description of the nano-structure of a CaO-FeO-SiO 2 slag was obtained by using molecular dynamic simulations in conjunction with previously obtained experimental data from X-ray and neutron pair distribution function studies. Iron was predominately 4- and 5-fold coordinated with oxygen, forming polyhedra in tetrahedral and pyramidal/triangular bipyramidal configuration. The [FeO x ] polyhedra were corner-shared to the silica tetrahedra, while the higher coordinated fractions (x = 5 or 6) seemed to prefer to be next to each other, sharing edges. Ca was mostly surrounded by 6 or 7 oxygens in polyhedra that are predominantly edge-sharing with other units. The obtained results fit the experimental data well and as such provide an accurate and realistic picture of the iron-rich slag structure. [ABSTRACT FROM AUTHOR]

Deep eutectic solvents (DESs) are mixtures of ionic compounds and molecular hydrogen bond donors. Due to the many components and their different interacting subgroups, they give rise to a plethora of many different interactions which can be studied by ab initio molecular dynamics simulations, because within this method all the forces are calculated on the fly and no parametrization prior to the calculation is necessary. Since DESs can be applied in gas capture, for example for SO 2 absorption, we performed ab initio molecular dynamics studies of both the pure choline chloride/glycerol DES and the same mixed with SO 2 . We identified the hydrogen bonding and other specific interactions between all components. With addition of SO 2 , we observed a decrease in the anion-OH group interplay, because the chloride anions form complexes with the SO 2 molecules. Furthermore, the SO 2 molecules are incorporated into the hydrophobic network and the interaction between the hydrogen bonds of all OH groups remain constant. This decrease of anion-OH interaction might be responsible for the more fluid state of the SO 2 -DESs mixture than the pure DES. [ABSTRACT FROM AUTHOR]

• α -amino amidines are in structure similar to their a-amino acid analogues. • Dipole moments are highly dependent on state and conformation of a molecule. • α -amino amidines in water are in an equilibrium between neutral and protonated state. • Amidine and carboxylic acid show significant differences in electronic structure. Among hypothetical alternative biochemistries, ammonia based life is one of the more promising ideas to investigate, due to the many similarities of water and ammonia as well as the existence of various ammonia based equivalents to prominent biomolecules. In this scenario α -amino amidines form the analogues to the α -amino acids, which can also be classified as the building blocks of life. Comparison of basic solvation behaviour between α -amino amidines and α -amino acids can provide insight into general chemical properties. To better understand the solvation of these compounds, we conducted ab initio molecular dynamics simulations for alanine, leucine, 2-aminopropionamidine and 2-amino-4-methylpentanamidine dissolved in 128 water molecules. We started simulations both from the neutral as well as from the zwitterionic form. For the α -amino amidines we observed protonation of the amidine group by water. Amino acids do not change spontaneously between the two states in our simulations. The molecular dipole moment is highly influenced by the state and conformation of the molecule and is a key property to trace in the course of the simulation. Structural analyses demonstrate the interactions of the compound with the surrounding solvent, solvation shells and hydrogen bonding. [ABSTRACT FROM AUTHOR]

Abstract: We present a short overview of our results which have been obtained from theoretical investigations during the period of the SPP-1191 priority program. The liquid state of imidazolium-based ionic liquids and protic ionic liquids has been studied intensively in our group not only mainly from ab initio molecular dynamics simulations, but also from classical molecular dynamics simulations. Hydrogen bonds and intermolecular forces have also been examined by quantum chemical methods, and their influence on molecular and macroscopic properties is reviewed here. We have extended our investigations to the gas phase which has been studied from both classical and ab initio molecular dynamics simulations. More insights into water(-impurities) ionic liquid interactions have been gained, and mixtures of ionic liquids have been explored. The mechanism of reactions in ionic liquids and solute ionic liquid relationships as well as cation and anion effects — which is reflected in either an active or a passive role of the ionic liquid — have been considered. [Copyright &y& Elsevier]

Using molecular dynamics simulations,we have studied the structureof three 1-butyl-1-methylpyrrolidinium ionic liquids whose anionsare triflate, bis(trifluoromethanesulfonyl)imide, and tris(pentafluoroethyl)trifluorophosphate.The structure of the bulk phase of the three ionic liquids has beeninterpreted using radial and spatial distribution functions and structurefactors that allows us to characterize the morphology of the polarand nonpolar domains present in this family of liquids. The size ofthe polar regions depends on the anion size, whereas the morphologyof the nonpolar domains is anion-independent. Furthermore, the surfaceordering properties of the ionic liquids and charge and density profileswere also studied using molecular simulations. The surface tensionof the liquid–vapor interfaces of these ionic liquids was alsopredicted from our molecular simulations. In addition, microscopicstructural analysis of orientational ordering at the interface anddensity profiles along the direction normal to the interface suggestthat the alkyl chains of the cation tend to protrude toward the vacuum,and the presence of the interface leads to a strong organization ofthe liquid phase in the region close to the interface. In the interfacialarea, the polar regions of the ionic liquids are more structured thanthose in the bulk phase, whereas the opposite behavior is observedfor the nonpolar regions. [ABSTRACT FROM AUTHOR]

Using molecular dynamics simulationswe have studied the structureof alkylsulfate-based ionic liquids: 1-ethyl-3-methylimidazolium n-alkylsulfate [C2C1im][CnSO4] (n= 2, 4, 6 and8). The structure of the different ionic liquids have been interpretedtaking into account radial and spatial distribution functions, andstructure factors, that allowed us to characterize the morphologyof the polar and nonpolar domains present in this family of liquids.The size of the nonpolar regions depends linearly on the anion alkylchain length. Furthermore, properties of the surface of ionic liquids,such as surface tension, ordering, and charge and density profiles,were studied using molecular simulation. We were able to reproducethe experimental values of the surface tension with a maximum deviationof 10%, and it was possible to relate the values of the surface tensionwith the structure of the liquid–vacuum interfaces. Microscopicstructural analysis of orientational ordering at the interface anddensity profiles along the direction normal to the interface suggestthat the alkyl chains of the anions tend to protrude toward the vacuum,and the presence of the interface leads to a strong organization ofthe liquid phase in the region close to the interface, stronger whenthe side-chain length of the anions increases. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations with an all-atom model were carried out to study the ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF6]. Analysis was carried out to characterize a number of structural and dynamic properties. It is found that the hydrogen bonds are weaker than expected, as indicated by their short lifetimes, which is due to the fast rotational motion of anions. Transport properties such as ion diffusion coefficients and ionic conductivity were also measured on the basis of long trajectories, and good agreement was obtained with experimental results. The phenomenon that electrical conductivity of ionic liquids deviates from the Nernst-Einstein relation was well reproduced in our work. On the basis of our analysis, we suggest that this deviation results from the correlated motion of cations and anions over time scales up to nanoseconds. In contrast, we find no evidence for long-lived ion-pairs migrating together. [ABSTRACT FROM AUTHOR]

• Molecular dipole moments of cationic and anionic dipoles. • Structure and dynamics. • IR spectra of an aqueous mixture of ionic liquids. In this study we compare the results of three different polarizable molecular dynamics force fields with an ab initio trajectory of the aqueous mixture of 1-butyl-3-methylimidazolium tetrafluoroborate and chloride, especially regarding their ability to describe static and dynamic phenomena. The discrepancies are discussed in terms of intra- and intermolecular force field parameters as well as the system size. We report significant differences in the derived diffusion coefficients and attribute them to system size, density and general discrepancies between ab initio and classical molecular dynamics simulations. In most cases, radial distribution functions show qualitative agreement; however, the overpolarization of chloride in the MD trajectories gives rises to unphysical results. Excellent agreement between dipolar distributions point out the importance of explicit polarizability in MD, while the comparison of computational and experimental IR spectra highlights the similarities between classical and ab initio dynamics in the low-wave number region and the differences around 1500 cm−1. [ABSTRACT FROM AUTHOR]