Browsing by Author "van Deventer, JSJ"

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    Density functional modelling of silicate and aluminosilicate dimerisation solution chemistry
    (Royal Society of Chemistry, 2011-02-14) White, CE; Provis, JL; Kearley, GJ; Riley, DP; van Deventer, JSJ
    Common throughout sol–gel chemistry, including zeolite synthesis, aluminosilicate glass formation and geopolymerisation, is the process of inorganic oxide polymerisation and deprotonation. In this investigation, some of the fundamental reactions occurring during zeolite synthesis and geopolymerisation at high pH are investigated using density functional theory (DFT), and are compared with: (i) existing values reported in the literature, and (ii) new and previously published DFT-derived data for similar silicate reactions at near-neutral pH. From the results it is seen that the energetics of deprotonation and dimerisation reactions depend greatly on the pH value, and these results correlate well with existing experimental values and trends. Hence, this investigation exemplifies that an accurate replication of the solution environment is crucial for obtaining useful theoretical results for species dissolved in non-ideal environments. © 2011, Royal Society of Chemistry
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    What is the structure of kaolinite? Reconciling theory and experiment
    (American Chemical Society, 2009-05-14) White, CE; Provis, JL; Riley, DP; Kearley, GJ; van Deventer, JSJ
    Density functional modeling of the crystalline layered aluminosilicate mineral kaolinite is conducted, first to reconcile discrepancies in the literature regarding the exact geometry of the inner and inner surface hydroxyl groups, and second to investigate the performance of selected exchange-correlation functionals in providing accurate structural information. A detailed evaluation of published experimental and computational structures is given, highlighting disagreements in space groups, hydroxyl bond lengths, and bond angles. A major aim of this paper is to resolve these discrepancies through computations. Computed structures are compared via total energy calculations and validated against experimental structures by comparing computed neutron diffractograms, and a final assessment is performed using vibrational spectra from inelastic neutron scattering. The density functional modeling is carried out at a sufficiently high level of theory to provide accurate structure predictions while keeping computational requirements low enough to enable the use of the structures in large-scale calculations. It is found that the best functional to use for efficient density functional modeling of kaolinite using the DMol(3) software package is the BLYP functional. The computed structure for kaolinite at 0 K has C-1 symmetry, with the inner hydroxyl group angled slightly above the a,b plane and the inner surface hydroxyls aligned close to perpendicular to that plane. © 2009, American Chemical Society