Ab initio molecular dynamics simulations have been performed for the first time on the room-temperature organic ionic liquid dimethyl imidazolium chloride [DMIM][Cl] using density functional theory. The aim is to compare the local liquid structure with both that obtained from two different classical force fields and from neutron scattering experiments. The local structure around the cation shows significant differences compared to both the classical calculations and the neutron results. In particular, and unlike in the gas-phase ion pair, chloride ions tend to be located near a ring C-H proton in a position suggesting hydrogen bonding. The results are used to suggest ways in which the classical potentials may be improved.

The behavior of a model ionic liquid (IL) confined between two flat parallel walls was studied at various interwall distances using computer simulations. The results focus both on structural and dynamical properties. Mass and charge density along the confinement axis reveal a structure of layers parallel to the walls that leads to an oscillatory profile in the electrostatic potential. Orientational correlation functions indicate that cations at the interface orient tilted with respect to the surface and that any other orientational order is lost thereafter. The diffusion coefficients of the ions exhibit a maximum as a function of the confinement distance, a behavior that results from a combination of the structure of the liquid as a whole and a faster molecular motion in the vicinity of the walls. We discuss the relevance of the present results and elaborate on topics that need further attention regarding the effects of ILs in the functioning of IL-based dye-sensitized solar cells.

Electronic structure problems are studied in condensed matter physics and theoretical chemistry to provide important insights into the properties of matter. This 2006 graduate textbook describes the main theoretical approaches and computational techniques, from the simplest approximations to the most sophisticated methods. It starts with a detailed description of the various theoretical approaches to calculating the electronic structure of solids and molecules, including density-functional theory and chemical methods based on Hartree-Fock theory. The basic approximations are thoroughly discussed, and an in-depth overview of recent advances and alternative approaches in DFT is given. The second part discusses the different practical methods used to solve the electronic structure problem computationally, for both DFT and Hartree-Fock approaches. Adopting a unique and open approach, this textbook is aimed at graduate students in physics and chemistry, and is intended to improve communication between these communities. It also serves as a reference for researchers entering the field.

We have been using atomistic simulation for the last 10 years to study properties of imidazolium-based ionic liquids. Studies of dissolved molecules show the importance of electrostatic interactions in both aromatic and hydrogen-bonding solutes. However, the local structure strongly depends upon ion-ion and solute-solvent interactions. We find interesting local alignments of cations at the gas-liquid and solid-liquid interfaces, which give a potential drop through the surface. If the solid interface is charged, this charge is strongly screened over distances of a few nanometres and this screening decays on a fast time scale. We have studied the sensitivity of the liquid structure to force-field parameters and show that results from ab initio simulations can be used in the development of force fields.

CO oxidation on TiO2 supported Au has been studied using density functional theory calculations. Important catalytic roles of the oxide have been identified: (i) CO oxidation occurs at the interface between Au and the oxide with a very small barrier; and (ii) O2 adsorption at the interface is the key step in the reaction. The physical origin of the oxide promotion effect has been further investigated: The oxide enhances electron transfer from the Au to the antibonding states of O2, giving rise to (i) strong ionic bonding between the adsorbed O2, Au, and the Ti cation; and (ii) a significant activation of O2 towards CO oxidation.

Articles you may be interested inCommunication: Regularizing binding energy distributions and thermodynamics of hydration: Theory and application to water modeled with classical and ab initio simulations Communication: Thermodynamics of water modeled using ab initio simulations Ab initio chemical potentials of solid and liquid solutions and the chemistry of the Earth's core We present a practical scheme for performing ab initio supercell calculations of charged slabs at constant electron chemical potential , rather than at constant number of electrons N e . To this end, we define the chemical potential relative to a plane ͑or ''reference electrode''͒ at a finite distance from the slab ͑the distance should reflect the particular geometry of the situation being modeled͒. To avoid a net charge in the supercell, and thus make possible a standard supercell calculation, we restore the electroneutrality of the periodically repeated unit by means of a compensating charge, whose contribution to the total energy and potential is subtracted afterwards. The ''constant '' mode enables one to perform supercell calculation on slabs, where the slab is kept at a fixed potential relative to the reference electrode. We expect this to be useful in modeling many experimental situations, especially in electro-chemistry.

The response of a room temperature molten salt to an external electric field when it is confined to a nanoslit is studied by molecular dynamics simulations. The fluid is confined between two parallel and oppositely charged walls, emulating two electrified solid-liquid interfaces. Attention is focused on structural, electrostatic, and dynamical properties, which are compared with those of the nonpolarized fluid. It is found that the relaxation of the electrostatic potential, after switching the electric field off, occurs in two stages. A first, subpicosecond process accounts for 80% of the decay and is followed by a second subdiffusive process with a time constant of 8 ps. Diffusion is not involved in the relaxation, which is mostly driven by small anion translations. The relaxation of the polarization in the confined system is discussed in terms of the spectrum of charge density fluctuations in the bulk.

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