Dr. Tristan Youngs

Honorary Lecturer

Tristan

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t.youngs@qub.ac.uk

Atomistic Simulation Centre School of Mathematics and Physics Queen's University Belfast University Road Belfast BT7 1NN Northern Ireland

Degrees, Awards and Honours

  • | B.Sc (Hons)
  • | PhD, University of Reading

Interests

    Most Recent Publications

    1. Effect of hydrophobic nanopatches within an ionic surface on the structure of liquids, Physical Chemistry Chemical Physics, 2011, 13, No. 2, pp. 582Abstract
      The structures of liquid water and isopropanol have been studied as a function of the size of a hydrophobic patch present in a model hydrophilic surface via molecular dynamics simulations. A significant anisotropy extending into the first few solvent layers is found over the patch which suggests implications for many real-world systems in which nanoscale heterogeneity is found.

    2. Dispersion interactions in room-temperature ionic liquids: Results from a non-empirical density functional, Physical Chemistry Chemical Physics, 2011, 13, No. 2, pp. 582, Journal of Chemical Physics, 2011, 135, pp. 154505Abstract

    3. Aten-An Application for the Creation, Editing, and Visualization of Coordinates for Glasses, Liquids, Crystals, and Molecules, Physical Chemistry Chemical Physics, 2011, 13, No. 2, pp. 582, Journal of Chemical Physics, 2011, 135, pp. 154505, Journal of Computational Chemistry, 2010, 31, No. 3, pp. 639
      doi: 10.1002/jcc.21359 Abstract
      Aten is a tool for Linux, Mac, and Windows platforms to ease the creation, editing, and visualization of coordinates for use in, for example, molecular dynamics simulations. The code handles gas-phase molecules in addition to crystals, surfaces, and liquids, providing standard tools to edit "by the atom" along with specific "by the box" methods suited to periodic systems, including full crystallographic spacegroup packing definitions. Visualization of systems encompasses the standard drawing styles and may be mixed with an arbitrary number of other basic objects, such as arrows and geometric objects allowing creation of scenes involving vector fields, coarse-grained particles, etc. Standard molecular mechanics forcefields can be read in, edited, applied to molecules using the built-in chemical typing language, and subsequently used to calculate energies and forces, minimize energies with respect to coordinates, decompose energies into contribution by molecule type, etc. Monte Carlo methods are available with which to generate random configurations of N-component systems, or solvate around molecules or in specific regions within existing configurations. Supported file formats are governed by user-defined "filters," which provide flexibility of input/output as well as the ability to define custom or extended formats of traditional files. Forcefield descriptions for loaded systems can be output and formatted for use as input to common codes. All features can be accessed by a comprehensive GUI and scripting language based on the C syntax. (C) 2009 Wiley Periodicals, Inc. J Comput Chem 31: 639-648, 2010

    All of Tristan's publications

    Alternatively

    Disordered Materials Group
    ISIS Facility
    Rutherford Appleton Laboratory

    ISIS Disordered Materials

    Research Synopsis



    Structural Studies of Ionic Liquids


    Example of calculated neutron scattering traces from different isotopic substitutions within the system


    Probability densities of chloride anions (blue) and 1,3-dimethylimidazolium cations (red) around a central cation as determined from molecular dynamics simulation

    Ionic liquids (ILs) are currently receiving much attention owing to their potential use as replacement solvents in organic synthesis. They are commonly composed of large organic cations (e.g. alkylimidazolium) and poorly coordinating inorganic anions (e.g. hexafluorophosphate, bistrifylamide) and have melting points close to ambient temperatures and wide liquidus ranges. The volatility of typical solvents employed in organic synthesis results in significant emission to the environment, but ILs have negligible vapour pressure making them potentially useful replacements. Furthermore, ILs are able to dissolve both organic and inorganic molecules allowing species to be brought together in one liquid phase forcing reaction homogeneity, and it has been shown that many organic reactions proceed well in ILs and in a significant number of cases are shown to be more selective and/or of higher yield.

    Understanding the microscopic liquid structure of these systems is important in order to understand the nature of the interactions existing between ions and dissolved species, and provides data which can further allow the guided design of new ionic liquids targetted for specific applications. In conjunction with QUILL and the School of Chemistry and Chemical Engineering we perform neutron scattering studies in order to probe the liquid phase (using the SANDALS instrument at Rutherford Appleton Laboratory), in conjunction with complementary molecular dynamics simulations.

    Related Publications:

    Liquid structure of the ionic liquid, 1-methyl-4-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide determined from neutron scattering and molecular dynamics simulations
    C. Hardacre, J. D. Holbrey, C. L. Mullan, M. Niewenhuyzen, T. G. A. Youngs, and D. T. Bowron
    J. Phys. Chem. B, 112, 8049-8056 (2008).

    Glucose solvation by the ionic liquid 1,3-dimethylimidazolium chloride: A simulation study
    T. G. A. Youngs, C. Hardacre, and J. D. Holbrey
    J. Phys. Chem. B, 111, 13765-13774 (2007).

    Structure and solvation in ionic liquids
    C. Hardacre, J. D. Holbrey, M. Niewenhuyzen, and T. G. A. Youngs
    Acc. Chem. Res., 40, 1146-1155 (2007).

    Molecular Dynamics of the Solid-Liquid Interface

    Map of average water dipole orientations as a function of position over an ionic NaCl-like surface containing a neutral patch of atoms. Liquid structure is considerably affected by even small sub-nanometre sized patches of atoms.

    Related Publications:

    Liquid Structure and Dynamics of Aqueous Isopropanol over Acidic γ-alumina Surfaces
    T. G. A. Youngs, D. Weber, L. F. Gladden, and C. Hardacre
    J. Phys. Chem. C, 113, 21342–21352 (2009)

    Effect of Uncharged Nanopatches on an Ionic Surface on the Structure and Dynamics of Confined Liquids
    T. G. A. Youngs and C. Hardacre
    Phys. Chem. Chem. Phys., 10.1039/C0CP01838D (2011)

    Aten - Create, Edit, and Visualise Atomic Coordinates


    Aten editing the crystal structure of cellulose, loaded from the CIF file

    Aten is a freeware tool available for Linux, Mac, and Windows, designed to be something useful to have to hand if you need to create from scratch some coordinates for your simulations, or edit existing ones. In particular, periodic systems such as liquids, glasses, and crystals are catered for. Along with the necessary rendering of molecular systems, grid data such as surfaces, probability densities can also be viewed at the same time. Aten is entirely written in C++/Qt4 and spare time, and is fully scriptable using its built-in command language.

    Will it read or write the coordinate format you need? Most likely. Aten uses filters to drive the input and output of data, which means that if your format isn't supported then with a little effort you can add support for it yourself. As well as this, Aten can read in molecular mechanics forcefield data and write out full forcefield specifications for your systems (again, using filters).

    Visit projectaten.net and try it out.

    Related Publications:

    Aten - An application for the creation, editing, and visualisation of coordinates for glasses, liquids, crystals, and molecules
    T. G. A. Youngs
    J. Comp. Chem., 31, 639–648 (2010)

    Force Matching to fit Ionic Liquid Forcefields


    Histograms generated from the final parameters from many hundreds of fits to the same data. Final (average) parameters are extracted from Gaussian fits to this data

    Any classical simulation is limited by the accuracy of the parameters used to represent the interactions present in the system, and for ionic liquids this is no exception. Of course, the predominant interaction in such media is electrostatic, and this can usually be well accounted for in classical simulations by the use of an appropriate set of charges. However, it is known that using charges derived from gas-phase calculations of molecules is not always ideal - for example, the resulting dipole of water in the gas phase is quite different from the actual dipole in the liquid phase. For ionic liquids the assumption of unit positive or negative charges in gas phase calculations on the ions is necessary, and befalls a similar problem since the effects of charge screening are not accounted for. Performing charge derivations based on calculations of the ion pair is an improvement, but in such cases the charge distribution is heavily conformation dependent.

    We have shown that the force matching approach can be used to recover an entire forcefield (including intramolecular geometric terms) from ab initio data on the liquid phase that better represents the structural aspects of the liquid. In addition, we have shown that a similar approach suggests that non-integer charges on the ions further improves not only the microscopic structure of the liquid, but also its energetics and dynamics, and without the need for expensive polarisable terms to be included in the forcefield. The conclusion is that such a choice of charges represents an average (i.e. static) picture of charge transfer present in the liquid, existing mostly through hudrogen bonding between ions. This study has so far been performed only for the ionic liquid 1,3-dimethylimidazolium chloride, but further investigations are underway with the hope to extend to systems more widely used in the literature.

    Related Publications:

    Application of static charge transfer within an ionic-liquid force field and its effect on structure and dynamics
    T. G. A. Youngs, and C. Hardacre
    ChemPhysChem, 9, 1548-1558 (2008).

    Development of complex classical force fields through force matching to ab initio data: Application to a room-temperature ionic liquid
    T. G. A. Youngs, M. G. Del Pópolo, and J. Kohanoff
    J. Phys. Chem. B, 110, 5697-5707 (2006).

    Ab Initio Molecular Dynamics Simulation of a Room Temperature Ionic Liquid
    M. G. Del Pópolo, R. M. Lynden-Bell, and J. Kohanoff
    J. Phys. Chem. B 109 5895-5902 (2005).

    Selective Separation of Actinides from Lanthanides (PhD)


    HOMO of a candidate ligand selected for study - two nitrogen atoms in the tridentate cavity possess most of the electron density of the orbital relevant to the coordination of the actinide

    It is envisaged that a potential route for the treatment of nuclear waste in order to reduce the length of time required for storage is the transmutation of the most radioactive isotopes into shorter-lived by-products. In this way, the required number of years required for subsequent storage can be reduced by several orders of magnitude. The elemental targets for this transmutation are the minor actinides which possess considerable half-lives - bombardment with thermal neutrons promotes decay into shorter-lived species. However, lanthanides are present in excess in the raw waste material and themselves effectively absorb neutrons preventing efficient transmution of the minor actinides.

    The selective separation of the target actinides, therefore, is paramount to the success of the procedure. In this work we examine the ability of multidentate nitrogen donor ligands to fulfil this task, studied by molecular dynamics (to determine likely conformations and partitioning aspects of the candidate ligands), ab initio calculations (to determine the relevant electron properties of known selective extractors), and predictive calculations based on quantitative structure activity relationships (QSARs, in order to determine new structures for study).

    Related Publications:

    QSAR studies of multidentate nitrogen ligands used in lanthanide and actinide extraction processes
    M. G. B. Drew, M. J. Hudson and T. G. A. Youngs
    J. Alloys Cmpds., 374, 408-415 (2004).

    Separation of lanthanides and actinides(III) using tridentate benzimidazole, benzoxazole and benzothiazole ligands
    M. G. B. Drew, C. Hill, M. J. Hudson, P. B. Iveson, C. Madic, L. Vaillant and T. G. A. Youngs
    New J. Chem., 28, 462-470 (2004).

    Solvent extraction and lanthanide complexation studies with new terdentate ligands containing two 1,3,5-triazine moieties
    M. G. B. Drew, C. Hill, M. J. Hudson, P. B. Iveson, C. Madic and T. G. A. Youngs
    Dalton Trans., 244-254 (2004).

    The coordination chemistry of 1,2,4-triazinyl bipyridines with lanthanide(III) elements - implications for the partitioning of americium(III)
    M. J. Hudson, M. G. B. Drew, M. R. StJ. Foreman, C. Hill, N. Huet, C. Madic and T. G. A. Youngs
    Dalton Trans., 1675-1685 (2003).

    Americium(III) and europium(III) solvent extraction studies of amide-substituted triazine ligands and complexes formed with ytterbium(III)
    N. Boubals, M. G. B. Drew, C. Hill, M. J. Hudson, P. B. Iveson, C. Madic, M. Russell and T. G. A. Youngs
    J. Chem. Soc. Dalton Trans., 55-62 (2002).