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  • 1
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    Interplay between the structure and dynamics in liquid and undercooled boron: An ab initio molecular dynamics simulation study (2014)
    American Institute of Physics (AIP)
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    Publication Date: 2014-12-18
    Description: In the present work, the structural and dynamic properties of liquid and undercooled boron are investigated by means of ab initio molecular dynamics simulation. Our results show that both liquid and undercooled states present a well pronounced short-range order (SRO) mainly due to the formation of inverted umbrella structural units. Moreover, we observe the development of a medium-range order (MRO) in the undercooling regime related to the increase of inverted umbrella structural units and of their interconnection as the temperature decreases. We also evidence that this MRO leads to a partial crystallization in the β-rhombohedral crystal below T = 1900 K. Finally, we discuss the role played by the SRO and MRO in the nearly Arrhenius evolution of the diffusion and the non-Arrhenius temperature dependence of the shear viscosity, in agreement with the experiment.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Transport properties and Stokes-Einstein relation in Al-rich liquid alloys (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-06-28
    Description: We use ab initio molecular dynamics simulations to study the transport properties and the validity of the Stokes-Einstein relation in Al-rich liquid alloys with Ni, Cu, and Zn as alloying elements. First, we show that the composition and temperature dependence of their transport properties present different behaviors, which can be related to their local structural ordering. Then, we evidence that the competition between the local icosahedral ordering and the local chemical ordering may cause the breakdown of the Stokes–Einstein relation even in the liquid phase. We demonstrate that this breakdown can be captured by entropy-scaling relationships developed by Rosenfeld and using the two-body excess entropy. Our findings provide a unique framework to study the relation between structure, thermodynamics, and dynamics in metallic melts and pave the way towards the explanation of various complex transport properties in metallic melts.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
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  • 3
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    The hydrogen diffusion in liquid aluminum alloys from ab initio molecular dynamics (2014)
    American Institute of Physics (AIP)
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    Publication Date: 2014-09-06
    Description: We study the hydrogen diffusion in liquid aluminum alloys through extensive ab initio molecular dynamics simulations. At the microscopic scale, we show that the hydrogen motion is characterized by a broad distribution of spatial jumps that does not correspond to a Brownian motion. To determine the self-diffusion coefficient of hydrogen in liquid aluminum alloys, we use a generalized continuous time random walk model recently developed to describe the hydrogen diffusion in pure aluminum. In particular, we show that the model successfully accounts the effects of alloying elements on the hydrogen diffusion in agreement with experimental features.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    Striking role of non-bridging oxygen on glass transition temperature of calcium aluminosilicate glass-formers (2014)
    American Institute of Physics (AIP)
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    Publication Date: 2014-06-20
    Description: Molecular dynamics simulations are used to study the structural and dynamic properties of calcium aluminosilicate, (CaO-Al 2 O 3 ) 1− x (SiO 2 ) x , glass formers along three joins, namely, R = 1, 1.57, and 3, in which the silica content x can vary from 0 to 1. For all compositions, we determined the glass-transition temperature, the abundances of the non-bridging oxygen, triclusters, and AlO 5 structural units, as well as the fragility from the temperature evolution of the α-relaxation times. We clearly evidence the role played by the non-bridging oxygen linked either to Al atoms or Si atoms in the evolution of the glass-transition temperature as well as of the fragility as a function of silica content along the three joins.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
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  • 5
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    Coupling between dynamic slowing down and chemical heterogeneity in a metallic undercooled liquid (2017)
    American Physical Society (APS)
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    Publication Date: 2017-04-29
    Description: Author(s): N. Jakse and A. Pasturel We investigate the connection between local structure and dynamics in the liquid and undercooled A l 93 C r 7 alloy using ab initio molecular dynamics simulations. In the liquid phase, we show the striking effects of Cr alloying on the atomic-scale structure, characterized by a heterogeneous local orderi… [Phys. Rev. B 95, 144210] Published Fri Apr 28, 2017
    Keywords: Inhomogeneous, disordered, and partially ordered systems
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
    Published by American Physical Society (APS)
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  • 6
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    Hydrogen diffusion in liquid aluminum from ab initio molecular dynamics (2014)
    American Physical Society (APS)
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    Publication Date: 2014-05-13
    Description: Author(s): N. Jakse and A. Pasturel Ab initio molecular dynamics simulations are used to describe the diffusion of hydrogen in liquid aluminum at different temperatures. Quasi-instantaneous jumps separating periods of localized vibrations around a mean position are found to characterize the hydrogen motion at the microscopic scale. Th... [Phys. Rev. B 89, 174302] Published Mon May 12, 2014
    Keywords: Dynamics, dynamical systems, lattice effects
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    Topics: Physics
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  • 7
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    Correlation between dynamic slowing down and local icosahedral ordering in undercooled liquid Al80Ni20 alloy (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-08-28
    Description: We use ab initio molecular dynamics simulations to study the correlation between the local ordering and the dynamic properties of liquid Al 80 Ni 20 alloy upon cooling. Our results evidence a huge increase of local icosahedral ordering (ISRO) in the undercooled regime which is more developed around Ni than Al atoms. We show that ISRO has a strong impact on self-diffusion coefficients of both species and is at the origin of their crossover from Arrhenius to non-Arrhenius behavior around a crossover temperature T X = 1000 K, located in the undercooled region. We also clearly identify that this temperature corresponds to the development of dynamic heterogeneities and to the breakdown of the Stokes-Einstein relation. At temperatures below this crossover, we find that the behavior of the diffusion and relaxation dynamics is mostly incompatible with predictions of the mode-coupling theory. Finally, an analysis of the van Hove function indicates that the crossover temperature T X marks the onset of a change in the diffusion mechanism from a normal flow to an activated process with hopping. From these results, the glass-forming ability of the alloy is discussed.
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    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
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  • 8
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    Relationship between structure and dynamics in liquid Al1−xNix alloys (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-08-25
    Description: Using ab initio molecular dynamics simulations, we study structural and dynamic properties of liquid Al-Ni alloys at T = 1795 K as a function of concentration. From partial pair-correlation functions and Bhatia-Thornton structure factors, we show a non-linear composition dependence of chemical short-range order. Additional analysis based on three-dimensional pair-analysis techniques evidences a strong interplay between icosahedral short-range order and chemical short-range order in the Ni-rich range. In examining transport properties like self-diffusion and inter-diffusion coefficients, we demonstrate a close relationship between the structural changes and the non-linear evolution of dynamic properties as a function of composition.
    Print ISSN: 0021-9606
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    Topics: Chemistry and Pharmacology , Physics
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  • 9
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    Relationship between structural and dynamic properties of Al-rich Al-Cu melts: Beyond the Stokes-Einstein relation (2016)
    American Physical Society (APS)
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    Publication Date: 2016-12-13
    Description: Author(s): N. Jakse and A. Pasturel We perform ab initio molecular dynamics simulations to study structural and transport properties in liquid A l 1 − x C u x alloys, with copper composition x ≤ 0.4 , in relation to the applicability of the Stokes-Einstein (SE) equation in these melts. To begin, we find that self-diffusion coefficients and visc… [Phys. Rev. B 94, 224201] Published Mon Dec 12, 2016
    Keywords: Inhomogeneous, disordered, and partially ordered systems
    Print ISSN: 1098-0121
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    Topics: Physics
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