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  • 1
    Electronic Resource
    Electronic Resource
    Determination of the mechanism of activation of the Ni-zeolite-Y catalyst by computational techniques (1994)
    Springer
    Journal of computer-aided materials design 1 (1994), S. 169-176 
    Details
    ISSN: 1573-4900
    Keywords: Zeolites ; Catalysis ; Lattice simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary Lattice simulations and quantum mechanical techniques are used to study the energetics involved in the activation of the Ni-zeolite-Y catalyst, which requires migration of the Ni2+ cation from the S1 (hexagonal prism) to the supercage. We show that the barrier to migration of the nickel ions may be overcome by interaction of the migrating ion with molecules such as H2O, NH3 and C2H2 in the supercage, thereby explaining the role of the latter species in the activation process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00708707
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  • 2
    Electronic Resource
    Electronic Resource
    Determination of acoustic phonon dispersion curves in layer silicates by inelastic neutron scattering and computer simulation techniques (1993)
    Springer
    Physics and chemistry of minerals 19 (1993), S. 520-527 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Inelastic neutron scattering and computer modelling techniques have been used to study acoustic phonons in several layer silicate minerals. Experimental measurements have been made on four layer silicate minerals; namely samples of muscovite, Fe-bearing muscovite, margarite and chlorite. The longitudinal acoustic modes propagating along the [0, 0, ξ] direction of muscovite and Fe-bearing muscovite were found to be the same, within experimental error. The longitudinal and transverse acoustic modes propagating along [0, 0, ξ] of muscovite have been calculated using computer simulation techniques based on lattice dynamics. The experimental and calculated longitudinal modes of muscovite are in excellent agreement, thereby demonstrating the complementary nature of both techniques. The shape of both experimental and calculated dispersion curves was found to be approximately sinusoidal, indicating that interatomic forces act principally between nearest-neighbour atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00203052
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  • 3
    Electronic Resource
    Electronic Resource
    An ab-initio Hartree-Fock study of α-quartz and stishovite (1990)
    Springer
    Physics and chemistry of minerals 17 (1990), S. 353-362 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract α-quartz and stishovite have been studied using a periodic ab-initio Hartree-Fock method in order to characterize the chemical nature of the Si-O bond and the way in which it changes with the coordination number of Si. Structural properties, including unit cell volume and c/a ratio have been optimized in order to evaluate the reliability of the method and the effect of the basis set. Density of states and electron charge density maps have been taken into account to investigate the electronic properties of the two systems and the rôle played by different orbitals. We also present comparisons with experimental X-ray emission data. The importance of d orbitals is stressed by our calculations, and a possible interpretation of the Si-O bond proposed. Quartz is found to be more covalent than stishovite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00200131
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  • 4
    Electronic Resource
    Electronic Resource
    Ab initio potentials for the calculation of the dynamical and elastic properties of α-quartz (1993)
    Springer
    Physics and chemistry of minerals 19 (1993), S. 392-400 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Ab initio LDF theory has been used to derive interatomic potentials for the Si-O and O-O interaction in α-quartz. The potentials have been used to study the lattice dynamical properties of α-quartz from 1 atm to 12.5 Gpa pressure. The results are compared with other calculated and experimentally derived potentials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202976
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  • 5
    Electronic Resource
    Electronic Resource
    The energetics and structure of the hydrogarnet defect in grossular: A computer simulation study (1994)
    Springer
    Physics and chemistry of minerals 20 (1994), S. 500-503 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract We have used computer simulation methods to model the structure and energetics of the hydrogarnet defect in grossular. The predicted structure is in good agreement with experimental data. The calculated energy for the reaction of water with grossular to form the hydrogarnet defect is 1.02 Ev (98 kJ mol-1). This low energy of reaction suggests that such defects will be common in garnets where they could play an important role in effecting processes such as atomic transport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00203220
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  • 6
    Electronic Resource
    Electronic Resource
    A computer simulation study of (OH) defects in olivine (1994)
    Springer
    Physics and chemistry of minerals 20 (1994), S. 515-518 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Recent experiments (Miller et al. 1987; Bell and Rossman 1992; Bai and Kohlstedt 1992) have shown that olivine, the dominant mineral in the Earth's upper mantle, can contain substantial amounts of water in the form of OH. There is uncertainty, however, as to the mechanisms by which water dissolves into the mineral structure and as to the site it occupies in the host lattice. We have therefore used atomistic computer simulation techniques based on the Born model of solids, to investigate the structures and energies of OH defects in olivine. Our calculations suggest that the most favourable route for incorporation of OH into olivine involves reactions with water accompanied by the reduction of ferric iron for which we obtain a solution energy of 0.46 eV. We propose therefore that the OH content will be largely controlled by the concentration of Fe3+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00203222
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  • 7
    Electronic Resource
    Electronic Resource
    LDF pseudopotential calculations of the α-quartz structure and hydrogarnet defect (1992)
    Springer
    Physics and chemistry of minerals 18 (1992), S. 389-392 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Ab initio LDF theory has been used to study the structure of the hydrogarnet defect in α-quartz. The predicted structure is in good agreement with the available sexperimental data. The techniques employed also yield a good model for the structure of α-quartz, giving an average Si-O bond length of 1.62 Å and average Si-O-Si angle of 142°.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00199421
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  • 8
    Electronic Resource
    Electronic Resource
    The catalytic activity and defect structure of zinc chromate (1991)
    Springer
    Catalysis letters 8 (1991), S. 385-389 
    Details
    ISSN: 1572-879X
    Keywords: Computer modelling ; non-stoichiometry ; oxide catalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Computer simulation techniques are used to develop defect models for the non-stoichiometric spinel with composition Zn1+xCr2−xO4 system. The results are used to provide an interpretation of the variation with composition of the catalytic activity of the monophasic material. We suggest that the increase in the catalytic activity with the Zn/Cr ratio is associated with an increased concentration of oxygen vacancies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00764201
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  • 9
    Electronic Resource
    Electronic Resource
    Determining the environment of transition metal ions in zeolitic catalysts: A combined computational and synchrotron-based study of nickel ions in zeolite-Y (1991)
    Springer
    Catalysis letters 8 (1991), S. 193-200 
    Details
    ISSN: 1572-879X
    Keywords: Zeolitic catalysts ; transition metal ions ; nickel ; computation ; environment ; EXAFS ; modelling catalysts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Computer modelling techniques are used to investigate the local structure of the zeolite framework around Ni2+ ions in the SI sites of Ni exchanged zeolite-Y. Our calculations show that there are pronounced inward relaxations (0.4 Å–0.6 Å) of the surrounding oxygen ions. The results allow a detailed rationalisation of recent EXAFS and diffraction studies on this zeolite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00764116
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  • 10
    Electronic Resource
    Electronic Resource
    EXAFS and molecular modelling studies of Rb1−xBixF1+2x (1994)
    Springer
    Journal of materials science 29 (1994), S. 2725-2733 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The fluorite structured mixed metal fluorides Rb1−x Bi x F1+2x (0.5≤x≥0.75) are exceptionally good F− ion conductors, a property which is clearly related to the mixed nature of the cation sub-lattice. Extended X-ray absorption fine structure (EXAFS) has been used to study the local structure of the two types of cation in Rb1−x Bi x F1+2x as a function of x. The results reveal marked differences for the local environments of Rb+ and Bi3+. Considerable short-range order develops as x deviates from 0.5, and this can be correlated with the relative conductivities of these materials. Molecular dynamics (MD) has been used to yield complementary information on structural properties. Simulations were performed for a series of temperatures between 80 K and 750 K. Excellent agreement between EXAFS and MD is obtained. A non-collinear interstitialcy mechanism is proposed for anion diffusion, which is seen to be the basis for more complex concerted processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00356824
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