Recent Publications

Jorge Kohanoff

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  1. Title: Solvation structure and transport of acidic protons in ionic liquids: A first-principles simulation study

    Author(s): Del Popolo M.G., Kohanoff J., Lynden-Bell R.M.

    Journal Of Physical Chemistry B, 110, No. 17, pp. 8798-8803 (MAY 4 2006)

    doi: 10.1021/jp0602326

    Ab initio simulations of a single molecule of HCl in liquid dimethyl imidazolium chloride [dmim][Cl] show that the acidic proton exists as a symmetric, linear ClHCl- species. Details of the solvation structure around this molecule are given. The proton-transfer process was investigated by applying a force along the antisymmetric stretch coordinate until the molecule broke. Changes in the free energy and local solvation structure during this process were investigated. In the reaction mechanism identified, a free chloride approaches the proton from the side. As the original ClHCl- distorts and the incoming chloride forms a new bond to the proton, one of the original chlorine atoms is expelled and a new linear molecule is formed.

  2. Title: Development of complex classical force fields through force matching to ab initio data: Application to a room-temperature ionic liquid

    Author(s): Youngs T.G.A., Del Popolo M.G., Kohanoff J.

    Journal Of Physical Chemistry B, 110, No. 11, pp. 5697-5707 (MAR 23 2006)

    doi: 10.1021/jp056931k

    Recent experimental neutron diffraction data and ab initio molecular dynamics simulation of the ionic liquid dimethylimidazolium chloride ([dmim]Cl) have provided a structural description of the system at the molecular level. However, partial radial distribution functions calculated front the latter, when compared to previous classical Simulation results, highlight some limitations in the structural description offered by force field-based simulations. With the availability of ab initio data it is possible to improve the classical description of [dmim]Cl by using the force matching approach, and the strategy for fitting complex force fields in their original functional form is discussed. A self-consistent optimization rnethod for the generation of classical potentials of general functional forill is presented and applied, and a force field that better reproduces the observed first principles forces is obtained. When used in Simulation, it predicts structural data which reproduces more faithfully that observed in the ab initio studies. Some possible refinements to the technique, its application, and the general Suitability of common potential energy functions used within many ionic liquid force fields are discussed.

  3. Title: Electronic structure calculations for solids and molecules: theory and computational methods

    Author(s): Kohanoff J.

    Cambridge University Press (JUN 2006)


    Full Text

    Electronic structure problems are studied in condensed matter physics and theoretical chemistry to provide important insights into the properties of matter. This 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.

  4. Title: Molecular electrostatic properties of ions in an ionic liquid

    Author(s): Prado C.E.R., Del Popolo M.G., Youngs T.G.A., Kohanoff J., Lynden-Bell R.M.

    Molecular Physics, 104, No. 15, pp. 2477-2483 (AUG 10 2006)

    doi: 10.1080/00268970600765748

    We have analysed the electronic wave functions from an ab initio simulation of the ionic liquid ( room temperature molten salt) dimethyl imidazolium chloride ([dmim][Cl] or [C(1)mim][CI]) using localized Wannier orbitals. This allows us to assign electron density to individual ions. The probability distributions of the ionic dipole moments for an isolated ion and for ions in solution are compared. The liquid environment is found to polarize the cation by about 0.7D and to increase the amplitude of the fluctuations in the dipole moments of both cation and anion. The relative changes in nuclear and electronic contributions are shown. The implications for classical force fields are discussed.