Browsing by Author "Kutteh, R"

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    Giant magnetoelastic effect at the opening of a spin-gap in Ba3BiIr2O9
    (American Chemical Society, 2012-01-26) Miiller, W; Avdeev, M; Zhou, Q; Kennedy, BJ; Sharma, N; Kutteh, R; Kearley, GJ; Schmid, S; Knight, KS; Blanchard, PER; Ling, CD
    As compared to 3d (first-row) transition metals, the 4d and 5d transition metals have much more diffuse valence orbitals. Quantum cooperative phenomena that arise due to changes in the way these orbitals overlap and interact, such as magnetoelasticity, are correspondingly rare in 4d and 5d compounds. Here, we show that the 6H-perovskite Ba3BiIr2O9, which contains 5d Ir4+ (S = 1/2) dimerized into isolated face-sharing Ir2O9 bioctahedra, exhibits a giant magnetoelastic effect, the largest of any known 5d compound, associated with the opening of a spin-gap at T* = 74 K. The resulting first-order transition is characterized by a remarkable 4% increase in Ir–Ir distance and 1% negative thermal volume expansion. The transition is driven by a dramatic change in the interactions among Ir 5d orbitals, and represents a crossover between two very different, competing, ground states: one that optimizes direct Ir–Ir bonding (at high temperature), and one that optimizes Ir–O–Ir magnetic superexchange (at low temperature). © 2012 American Chemical Society
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    Initial assessment of an empirical potential as a portable tool for rapid investigation of Li+ Diffusion in Li+-Battery cathode materials
    (American Chemical Society, 2014-04-30) Kutteh, R; Avdeev, M
    Substantial research activity is currently invested in the pursuit of next generation cathode materials for rechargeable Li-ion batteries. We carry out an initial assessment of the suitability of a recently described empirical potential [J. Phys. Chem. B 2006, 110, 11780] as a rapid, portable, and at least qualitatively accurate computational tool for screening large numbers of potential cathode materials for favorable Li-ion transport capabilities. Selected materials can then be examined more elaborately with more accurate but computationally more expensive first-principles approaches. As test systems for our initial assessment, we chose the group of phosphate olivines LiMPO4 (M = Mn, Fe, Co, Ni), promising candidates for next generation cathode materials and subject of numerous experimental and computational studies. To conduct the assessment, we determined the ground state structures of LiMPO4 from geometry optimizations with this empirical potential and with density functional theory (DFT) and computed activation barriers of Li-ion diffusion in LiMPO4 from molecular dynamics simulations based on the empirical potential and from minimum-energy-path DFT calculations. We show that structural results generated by the empirical potential are in good agreement with the DFT and experimental results and that barrier results produced by this potential are in good agreement with the DFT results and often in better agreement than values generated by custom parametrized empirical potentials. © 2014, American Chemical Society.
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    Methyl dynamics flattens barrier to proton transfer in crystalline tetraacetylethane
    (American Chemical Society, 2012-03-08) Kearley, GJ; Stare, J; Kutteh, R; Daemen, LL; Hartl, MA; Eckert, J
    We analyze the interplay between proton transfer in the hydrogen-bond bridge, O center dot center dot center dot H center dot center dot center dot O, and lattice dynamics in the model system tetraacetylethane (TAB) (CH(3)CO)(2)CH=CH(COCH(3))(2) using density functional theory. Lattice dynamics calculations and molecular dynamics simulations are validated against neutron scattering data. Hindrance to the cooperative reorientation of neighboring methyl groups at low temperatures gives a preferred O atom for the bridging proton. The amplitude of methyl torsions becomes larger with increasing temperature, so that the free-energy minimum for the proton becomes flat over 0.2 angstrom. For the isolated molecule, however, we show an almost temperature-independent symmetric double-well potential persists. This difference arises from the much higher barriers to methyl torsion in the crystal that make the region of torsional phase space that is most crucial for symmetrization poorly accessible. Consequently, the proton-transfer potential remains asymmetric though flat at the base, even at room temperature in the solid. © 2012, American Chemical Society.
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    Rigid body dynamics approach to Stokesian dynamics simulations of nonspherical particles
    (American Institute of Physics, 2010-05-07) Kutteh, R
    We describe an algorithm for performing Stokesian dynamics (SD) simulations of suspensions of arbitrary shape rigid particles with hydrodynamic interactions, modeled as rigid groups of spheres, the hydrodynamic mobility matrix of which is accurately computable by several established schemes for spheres. The algorithm is based on Stokesian rigid body equations of translational and rotational motion, which we have derived by an approach formally analogous to that of Newtonian rigid body dynamics. Particle orientation is represented in terms of Euler parameters (quaternion of rotation). This rigid body SD algorithm (RBSDA) complements recently described constraint SD algorithms [ R. Kutteh, J. Chem. Phys. 119, 9280 (2003) ; R. Kutteh, Phys. Rev. E 69, 011406 (2004) ], over which it offers the same computational advantages in imposing total rigidity that the basic rigid body molecular dynamics (MD) algorithm offers over constraint MD algorithms. We show that SD simulation results generated with the RBSDA, in bounded and unbounded geometries, agree very well with those from experiment and other SD and non-SD methods, and are numerically identical to those from a constraint SD algorithm, HSHAKE. Finally, for completeness we also describe a third (additional to the constraint SD and rigid body SD approaches) more traditional approach for SD simulations of arbitrary shape rigid particles modeled as rigid groups of spheres. © 2010, American Institute of Physics
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    Scientific computing support for neutron scattering experiments at ANSTO
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2018-11-19) Kutteh, R
    The purpose of the scientific computing support at ANSTO is to aid in the interpretation of both structural and dynamical data from the neutron scattering instruments using atomistic modelling calculations. Most of these calculations are done with ab initio scientific software packages based on Density Functional Theory, including VASP, WIEN2K, ABINIT, SIESTA, PHONON, and QUANTUM ESPRESSO, although some are performed with packages based on classical force fields, such as LAMMPS, DL_POLY, NAMD, and GULP. Analysis of the results of these calculations exploits tools such as VMD, NMOLDYN, XCRYSDEN, and ISAACS, in addition to in-house code. Calculations and analysis are carried out locally on a scientific computing Linux cluster comprising 624 ACNS dedicated cores and 1416 ANSTO shared cores, with jobs managed by PBS. We give a brief overview of all of the above capabilities and an example of a typical calculation/analysis. © The Authors.
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    Scientific computing support for neutron scattering experiments at ANSTO
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Kutteh, R
    The purpose of the scientific computing support at ANSTO is to aid in the interpretation of both structural and dynamical data from the neutron scattering instruments using atomistic modelling calculations. Most of these calculations are done with ab initio scientific software packages based on Density Functional Theory, including VASP, WIEN2K, ABINIT, SIESTA, PHONON, and QUANTUM ESPRESSO, although some are performed with packages based on classical force fields, such as LAMMPS, DL_POLY, NAMD, and GULP. Analysis of the results of these calculations exploits tools such as VMD, NMOLDYN, XCRYSDEN, and ISAACS, in addition to in-house code. Calculations and analysis are carried out locally on a scientific computing Linux cluster comprising 624 ACNS dedicated cores and 1416 ANSTO shared cores, with jobs managed by PBS. We give a brief overview of all of the above capabilities and an example of a typical calculation/analysis.
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    Scrutinizing negative thermal expansion in MOF-5 by scattering techniques and ab initio calculations
    (Royal Society of Chemistry, 2012-09-14) Lock, N; Christensen, M; Wu, Y; Peterson, VK; Thomsen, MK; Piltz, RO; Ramirez-Cuesta, AJ; McIntyre, GJ; Noren, K; Kutteh, R; Kepert, CJ; Kearley, GJ; Iversen, BB
    Complementary experimental techniques and ab initio calculations were used to determine the origin and nature of negative thermal expansion (NTE) in the archetype metal-organic framework MOF-5 (Zn4O(1,4-benzenedicarboxylate)3). The organic linker was probed by inelastic neutron scattering under vacuum and at a gas pressure of 175 bar to distinguish between the pressure and temperature responses of the framework motions, and the local structure of the metal centers was studied by X-ray absorption spectroscopy. Multi-temperature powder- and single-crystal X-ray and neutron diffraction was used to characterize the polymeric nature of the sample and to quantify NTE over the large temperature range 4-400 K. Ab initio calculations complement the experimental data with detailed information on vibrational motions in the framework and their correlations. A uniform and comprehensive picture of NTE in MOF-5 has been drawn, and we provide direct evidence that the main contributor to NTE is translational transverse motion of the aromatic ring, which can be dampened by applying a gas pressure to the sample. The linker motion is highly correlated rather than local in nature. The relative energies of different framework vibrations populated in MOF-5 are suggested by analysis of neutron diffraction data. We note that the lowest-energy motion is a librational motion of the aromatic ring which does not contribute to NTE. The libration is followed by transverse motion of the linker and the carboxylate group. These motions result in unit-cell contraction with increasing temperature. © 2012, Royal Society of Chemistry
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    Structures, phase transitions, hydration, and ionic conductivity of Ba4Nb2O9
    (American Chemical Society, 2009-08-25) Ling, CD; Avdeev, M; Kutteh, R; Kharton, VV; Yaremchenko, AA; Fialkova, S; Sharma, N; Macquart, RB; Hoelzel, M; Gutmann, MJ
    Ba4Nb2O9 is shown to have two basic polymorphs: a high-temperature γ phase, which represents an entirely new structure typed and a low-temperature (x phase, which has the rare Sr4Ru2O9 structure type. The phases are separated by a reconstructive phase transition at similar to 1370 K, the kinetics of which are sufficiently slow that the γ phase can easily be quenched to room temperature. Below similar to 950 K, both (α and γ phases absorb significant amounts of water. In the case of the γ phase, protons from absorbed water occupy ordered positions in the structure, giving rise to a stoichiometric phase γ-III-Ba4Nb2O9.1/3H(2)O at room temperature. γ-III-Ba4Nb2O9-1/3H(2)O partially dehydrates, at similar to 760 K to give another stoichiometric phase γ-II-Ba4Nb2O9.1/3H(2)O, which completely dehydrates at similar to 950 K to γ-I- Ba4Nb2O9. The hydrated γ phases exhibit faster protonic and oxide ionic transport than the hydrated (x phases because of the presence in the γ phases of 2D layers containing Nb5+ cations with unusually low oxygen coordination numbers (4 or 5) separated by discrete OH groups. Hydration appears to play an important role in stabilizing the γ phases at low temperatures, with the γ -> α transition oil reheating a quenched sample occurring at higher temperatures in humid atmospheres. © 2009, American Chemical Society
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    Synthesis, crystal structure, electrical properties, and sodium transport pathways of the new arsenate Na4Co7(AsO4)6
    (Elsevier, 2016-07-01) Ben Smida, Y; Marzouki, R; Georges, S; Kutteh, R; Avdeev, M; Guesmi, A; Zid, MF
    A new sodium cobalt (II) arsenate Na4Co7(AsO4)6 has been synthesized by a solid-state reaction and its crystal structure determined from single crystal X-ray diffraction data. It crystallizes in the monoclinic system, space group C2/m, with a=10.7098(9) Å, b=14.7837(9) Å, c=6.6845(7) Å, and β=105.545(9)°. The structure is described as a three-dimensional framework built up of corner-edge sharing CoO6, CoO4 and AsO4 polyhedra, with interconnecting channels along [100] in which the Na+ cations are located. The densest ceramics with relative density of 94% was obtained by ball milling and optimization of sintering temperature, and its microstructure characterized by scanning electron microscopy. The electrical properties of the ceramics were studied over a temperature interval from 280 °C to 560 °C using the complex impedance spectroscopy over the range of 13 MHz–5 Hz. The ionic bulk conductivity value of the sample at 360 °C is 2.51 10−5 S cm−1 and the measured activation energy is Ea=1 eV. The sodium migration pathways in the crystal structure were investigated computationally using the bond valence site energy (BVSE) model and classical molecular dynamics (MD) simulations. © 2016 Elsevier Inc.