Search results for "Pair distribution function"
showing 10 items of 13 documents
Strongly confined fluids: Diverging time scales and slowing down of equilibration
2016
The Newtonian dynamics of strongly confined fluids exhibits a rich behavior. Its confined and unconfined degrees of freedom decouple for confinement length $L \to 0$. In that case and for a slit geometry the intermediate scattering functions $S_{\mu\nu}(q,t)$ simplify, resulting for $(\mu,\nu) \neq (0,0)$ in a Knudsen-gas like behavior of the confined degrees of freedom, and otherwise in $S_{\parallel}(q,t)$, describing the structural relaxation of the unconfined ones. Taking the coupling into account we prove that the energy fluctuations relax exponentially. For smooth potentials the relaxation times diverge as $L^{-3}$ and $L^{-4}$, respectively, for the confined and unconfined degrees of…
Preparation and characterization of Pd2Sn nanoparticles
2007
We report a non-aqueous solution preparation of Pd{sub 2}Sn nanoparticles with sizes near 20 nm. The intermetallic compound with the Co{sub 2}Si structure has been characterized using transmission electron microscopy, Rietveld refinement of synchrotron X-ray and neutron powder diffraction, and real-space pair distribution function analysis of high-energy synchrotron X-ray scattering. We also present a description of the electronic structure of this covalent intermetallic using density functional calculations of the electronic structure.
A real-space approach to the analysis of stacking faults in close-packed metals: G(r) modelling and Q-space feedback
2019
An R-space approach to the simulation and fitting of a structural model to the experimental pair distribution function is described, to investigate the structural disorder (distance distribution and stacking faults) in close-packed metals. This is carried out by transferring the Debye function analysis into R space and simulating the low-angle and high-angle truncation for the evaluation of the relevant Fourier transform. The strengths and weaknesses of the R-space approach with respect to the usual Q-space approach are discussed.
Préparation et spéciation d’oxo-clusters de métaux du bloc p
2022
The main subject of this thesis is the use of Pair Distribution Function (PDF) analysis for solution phase speciation during metal-cluster growth. The PDF method allows the extraction of structural information from a sample in the form of an atom-atom distance distribution via Fourier transform of synchrotron X-ray scattering data. The growth mechanisms of two solution-based systems are analysed in this thesis. Precursor materials are synthesized through a mechanochemical method that was developed and shown to be able to access a wide range of related systems.Mechanochemical routes of synthesizing bismuth Active Pharmaceutical Ingredients (APIs) were investigated and optimised. Samples were…
Properties of condensed spin-aligned atomic hydrogen from variational calculations
1979
The optimal Jastrow-type ground-state wave function of spin-aligned atomic hydrogen is calculated using the pair potential of Kolos and Wolniewicz. The optimization is performed by solving the Euler equation in the hypernetted chain approximation. Accurate energies as well as pair-distribution functions are obtained. The Bose-Einstein condensate fraction is evaluated from the one-particle momentum distribution. The pair distribution function is also used to obtain stability criteria for the system and minimal values for the aligning magnetic field are calculated at low densities. The resulting values of the minimal aligning fields are considerably higher than those obtained previously.
Structure of Liquids
2014
An Introduction to the description of the static structure of simple liquids is given. The principle quantity, which describes this structure is the structure factor, which can be measured with neutron and X-ray diffraction. The structure factor is the Fourier transform of the radial pair distribution function, which describes the statistics of the atoms around a given one. Several theories are introduced for calculating this quantities. It is shown that the structure of liquid metals is dominated by their hardcore repulsion. In the low-wavenumber limit the structure factor is related to the compressibility of the liquid. In this limit deviations from the hard-core model become importent, w…
Pressure-induced amorphization of YVO4:Eu3+ nanoboxes
2016
A structural transformation from the zircon-type structure to an amorphous phase has been found in YVO4:Eu3+ nanoboxes at high pressures above 12.7 GPa by means of x-ray diffraction measurements. However, the pair distribution function of the high-pressure phase shows that the local structure of the amorphous phase is similar to the scheelite-type YVO4. These results are confirmed both by Raman spectroscopy and Eu3+ photoluminescence which detect the phase transition to a scheelite-type structure at 10.1 and 9.1 GPa, respectively. The irreversibility of the phase transition is observed with the three techniques after a maximum pressure in the upstroke of around 20 GPa. The existence of two …
Molecular dynamics simulations of colloids: Supercooled Yukawa systems
2007
We performed molecular dynamics simulations on one and two component Yukawa systems. Cooling the system down and inspecting pair distribution functions (pdf) and bond correlation functions (bcf) we found the one component system to crystallize into a bcc-like lattice rather than an fcc lattice which is the stable phase of the simulated system at low temperatures. Upon cooling the two component system freezes into a glassy state without exhibiting crystalline structure in pdf or bcf. We define particle excess functions which show that spacial fluctuations in the number density of particles of the different components decay quite slowly. Therefore we believe that a well defined state of the t…
A real-space approach to the analysis of stacking faults in close-packed metals: Modelling and Q-space feedback Longo Alessandro
2020
An R-space approach to the simulation and fitting of a structural model to the experimental pair distribution function is described, to investigate the structural disorder (distance distribution and stacking faults) in close-packed metals. This is carried out by transferring the Debye function analysis into R space and simulating the low-angle and high-angle truncation for the evaluation of the relevant Fourier transform. The strengths and weaknesses of the R-space approach with respect to the usual Q-space approach are discussed.
Real-Time Observation of “Soft” Magic-Size Clusters during Hydrolysis of the Model Metallodrug Bismuth Disalicylate
2021
International audience; Colloidal bismuth therapeutics have been used for hundreds of years, yet remain mysterious. Here we report an X-ray pair distribution function (PDF) study of the solvolysis of bismuth disalicylate, a model for the metallodrug bismuth subsalicylate (Pepto-Bismol). This reveals catalysis by traces of water, followed by multistep cluster growth. The ratio of the two major species, {Bi9O7} and {Bi38O44}, depends on exposure to air, time, and the solvent. The solution-phase cluster structures are of significantly higher symmetry in comparison to solid-state analogues, with reduced off-center Bi3+ displacements. This explains why such “magic-size” clusters can be both stab…