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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]

We applied the binary Quantum Cluster Equilibrium (bQCE) method to a number of alkylammonium-based protic ionic liquids in order to predict boiling points, vaporization enthalpies, and proton activities. The theory combines statistical thermodynamics of van-der-Waals-type clusters with ab initio quantum chemistry and yields the partition functions (and associated thermodynamic potentials) of binary mixtures over a wide range of thermodynamic phase points. Unlike conventional cluster approaches that are limited to the prediction of thermodynamic properties, dissociation reactions can be effortlessly included into the bQCE formalism, giving access to ionicities, as well. The method is open to quantum chemical methods at any level of theory, but combination with low-cost composite density functional theory methods and the proposed systematic approach to generate cluster sets provides a computationally inexpensive and mostly parameter-free way to predict such properties at good-to-excellent accuracy. Boiling points can be predicted within an accuracy of 50 K, reaching excellent accuracy for ethylammonium nitrate. Vaporization enthalpies are predicted within an accuracy of 20 kJ mol−1 and can be systematically interpreted on a molecular level. We present the first theoretical approach to predict proton activities in protic ionic liquids, with results fitting well into the experimentally observed correlation. Furthermore, enthalpies of vaporization were measured experimentally for some alkylammonium nitrates and an excellent linear correlation with vaporization enthalpies of their respective parent amines is observed. [ABSTRACT FROM AUTHOR]

Car-Parinello molecular dynamics (CPMD) simulations of the liquid imidazolium chloride/Al[Cl.sub.3] by inserting one pair of [[C.sub.2][C.sub.1]im] into liquid Al[Cl.sub.3] forming an acidic mixture is described. Large anions within the equilibrium phase are found for both simulations and these large anion species are formed to account for the lack of electrons present in the acidic melt.

A vibrational analysis of 2-fold hydrogen bonds between an isophthalic amide donor and different acceptors is described. The results have indicated that the pronounced blue shift of the C-H stretch mode is basically caused by the fact that the acceptor is fixed directly above this group due to the 2-fold hydrogen bond.

The idea of detecting a hydrogen bond solely on one single quantum chemically determined descriptor is extended. It is demonstrated that a classification according to acceptor atoms of the hydrogen-bonded complexes can give more accurate results.

The quantum cluster equilibrium method is applied to model binary systems of molecular solvents. We minimize the computational effort as well as the experimental input and present the results obtained for the completely miscible acetonitrile/acetone, benzene/acetone, and water/acetone systems, as well as for the hardly misciblewater/benzene system. Only clusters of sizes up to n = 3 are applied and these are optimized employing the low-cost functional PBEh-3c. The thermodynamic functions of the pure liquids are in reasonable agreement with experiments. For both non-water containing binary systems, the Gibbs energy of mixing can be reproduced with an accuracy of ≈0.25 kJ/mol. Water containing systems are not sufficiently described by small clusters. The empirical mean-field parameter amf and exclusion volume scaling parameter bxv which depend on the experimental input are approximated by linear interpolation between their neat liquids' reference values. This makes the approach independent from the experimental data of the binary system. Despite the roughness of the approximation as well as the small size of the cluster sets, the approach is able to correctly predict the mixing behavior of all acetone systems. The benzene/water system is correctly predicted to be non-miscible at most mole fractions. A small range at high benzene concentrations (x > 0.8) is falsely predicted to be miscible. [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]

Chiral, enantiopure metallo-supramolecular rhombs self-assemble in solution through coordination of bis-pyridyl-substituted ligands with (en)M(NO3)2. Characterization by nuclear magnetic resonance (NMR) and circular dichroism (CD) spectroscopy in solution and by electospray ionization Fourier transform ion cyclotron resonance (ESI-FT-ICR) mass spectrometry in the gas phase suggests that an equilibrium exists in water/methanol of a major 2:2 complex and a minor 3:3 complex of ligands and metal corners.

Vertical and adiabatic excitations of the s-tetrazine molecule, small clusters with water molecules and a single s-tetrazine molecule within 60 water molecules using periodic boundary conditions is studied. They achieved a consistent description of s-tetrazine from the isolated molecule to full solvation in water.

The way in which the standard population analysis can be utilized for a semiquantitative analysis of intermolecular interactions is presented. The report stated that the ability to extract additional information on the system from its electronic structure was offered by increasing availability of wave functions for large many-atom systems in molecular dynamics simulations-either in CPMD simulations or in single-point calculations on MD snapshots.

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 deuteron quadrupole coupling constant of water together with dimethyl sulfoxide was studied using computer simulations.