Configurational lattice dynamics: The phase diagram of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Rh</mml:mi><mml:mo>−</mml:mo><mml:mi mathvariant="normal">Pd</mml:mi></mml:mrow></mml:math>

Cienfuegos, C; Isoardi, E. P.; Barrera, Gustavo D.

doi:10.1103/physrevb.71.144202

Cited by 7 publications

(3 citation statements)

References 21 publications

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“…Though presently available computational resources make it possible to minimize the static energy with respect to this set of nine coordinates, it is currently too costly to optimize the whole set of variables by carrying out fully dynamic optimizations. For several systems that include ionic solids, 27 metals, 28 and even polyethylene 29 with force field potentials, it has already been shown that the use of the zero internal stress static approximation 29 (ZSISA) is a very good approximation for the evaluation of properties such as free energies, enthalpies, entropies, heat capacities, and thermal expansion. In this approximation, only external strains are relaxed fully dynamically while internal degrees of freedom are relaxed in the static approximation.…”

Section: Theoretical Methodsmentioning

confidence: 99%

The Vibrational Spectrum and Ultimate Modulus of Polyethylene

et al. 2006

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We have performed the first completely ab initio lattice dynamics calculation of the full orthorhombic cell of polyethylene using periodic density functional theory in the local density approximation (LDA) and the generalized gradient approximation (GGA). Contrary to current perceptions, we show that LDA accurately describes the structure whereas GGA fails. We emphasize that there is no parametrization of the results. We then rigorously tested our calculation by computing the phonon dispersion curves across the entire Brillouin zone and comparing them to the vibrational spectra, in particular the inelastic neutron scattering (INS) spectra, of polyethylene (both polycrystalline and aligned) and perdeuteriopolyethylene. The Γ-point frequencies (where the infrared and Raman active modes occur) are in good agreement with the latest low temperature data. The near-perfect reproduction of the INS spectra, gives confidence in the results and allows us to deduce a number of physical properties including the elastic moduli, parallel and perpendicular to the chain. We find that the Young's modulus for an infinitely long, perfectly crystalline polyethylene is 360.2 GPa at 0 K. The highest experimental value is 324 GPa, indicating that current high modulus fibers are ∼90% of their maximum possible strength.

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Section: Theoretical Methodsmentioning

confidence: 99%

The Vibrational Spectrum and Ultimate Modulus of Polyethylene

et al. 2006

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“…In the random selection strategy, initial arrangements are chosen at random and the convergence of the ensemble average with number of optimized configurations is analysed. A few randomly chosen arrangements have been sufficient for the calculation of thermodynamic and structural properties in oxide [21], mineral [13] and alloy [23] solid solutions at high T , when a large fraction of all minima is populated. However, in order to analyse the convergence of the ensemble averages with number of configurations we must first construct an appropriate grid where we distribute the atoms for the structural optimizations.…”

Section: Strategies For Mapping the Individual Basins On The Pesmentioning

confidence: 99%

Average and local structure of α-CuI by configurational averaging

Mohn¹,

Stølen²

2007

J. Phys.: Condens. Matter

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Configurational Boltzmann averaging together with density functional theory are used to study in detail the average and local structure of the superionic α-CuI. We find that the coppers are spread out with peaks in the atom-density at the tetrahedral sites of the fcc sublattice of iodines. We calculate Cu–Cu, Cu–I and I–I pair radial distribution functions, the distribution of coordination numbers and the distribution of Cu–I–Cu, I–Cu–I and Cu–Cu–Cu bond-angles. The partial pair distribution functions are in good agreement with experimental neutron diffraction—reverse Monte Carlo, extended x-ray absorption fine structure and ab initio molecular dynamics results. In particular, our results confirm the presence of a prominent peak at around 2.7 Å in the Cu–Cu pair distribution function as well as a broader, less intense peak at roughly 4.3 Å. We find highly flexible bonds and a range of coordination numbers for both iodines and coppers. This structural flexibility is of key importance in order to understand the exceptional conductivity of coppers in α-CuI; the iodines can easily respond to changes in the local environment as the coppers diffuse, and a myriad of different diffusion-pathways is expected due to the large variation in the local motifs.

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“…The XRD profile of the RhPd/CeO 2 -C catalyst shows an intense asymmetric peak with a shoulder at low d hkl values. The appearance of this peak can be ascribed to a reorganization accompanied by an increase of the crystallinity of the RhPd nanoparticles, and its asymmetry is indicative of the presence of more than one type of RhPd alloy (Rh and Pd are miscible at this temperature in a wide range [38]). A similar XRD peak is recorded for RhPd over the sample RhPd/CeO 2 -R after the reduction treatment, but with a much lower intensity, which can be explained by a smaller particle size of RhPd nanoparticles on ceria nanorods compared to that of RhPd nanoparticles on ceria nanocubes in accordance with STEM results.…”

Section: Catalytic Performancementioning

confidence: 99%

The influence of nano-architectured CeO supports in RhPd/CeO2 for the catalytic ethanol steam reforming reaction

Divins

Casanovas

et al. 2015

Catalysis Today

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a b s t r a c tThe ethanol steam reforming (ESR) reaction has been tested over RhPd supported on polycrystalline ceria in comparison to structured supports composed of nanoshaped CeO2 cubes and CeO2 rods tailored toward the production of hydrogen. At 650-700 K the hydrogen yield follows the trend RhPd/CeO2 -cubes > RhPd/CeO2 -rods > RhPd/CeO2 -polycrystalline, whereas at temperatures higher than 800 K the catalytic performance of all samples is similar and close to the thermodynamic equilibrium. The improved performance of RhPd/CeO2 -cubes and RhPd/CeO2 -rods for ESR at low temperature is mainly ascribed to higher water-gas shift activity and a strong interaction between the bimetallic-oxide support interaction. STEM analysis shows the existence of RhPd alloyed nanoparticles in all samples, with no apparent relationship between ESR performance and RhPd particle size. X-ray diffraction under operating conditions shows metal reorganization on {1 0 0} and {1 1 0} ceria crystallographic planes during catalyst activation and ESR, but not on {1 1 1} ceria crystallographic planes. The RhPd reconstructing and tuned activation over ceria nanocubes and nanorods is considered the main reason for better catalytic activity with respect to conventional catalysts based on polycrystalline ceria.

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Configurational lattice dynamics: The phase diagram ofRh−Pd

Cited by 7 publications

References 21 publications

The Vibrational Spectrum and Ultimate Modulus of Polyethylene

The Vibrational Spectrum and Ultimate Modulus of Polyethylene

Average and local structure of α-CuI by configurational averaging

The influence of nano-architectured CeO supports in RhPd/CeO2 for the catalytic ethanol steam reforming reaction

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