DYNAMIC MECHANISM OF LIQUID–GLASS TRANSITION FOR Mg7Zn3 ALLOY

2013 ◽  
Vol 27 (10) ◽  
pp. 1350071 ◽  
Author(s):  
ZHAO-YANG HOU ◽  
RANG-SU LIU ◽  
CHUN-LONG XU ◽  
XIAO-TING LI
Keyword(s):  
Glass Transition ◽  
Potential Energy ◽  
Liquid Glass ◽  
Dynamic Properties ◽  
Dynamic Mechanism ◽  
Relaxation Processes ◽  
Potential Energy Landscape ◽  
Temperature Dependences ◽  
Lower Mobility ◽  
Dynamics Simulations

The dynamic mechanism of liquid–glass transition for Mg 7 Zn 3 alloy is studied by the molecular dynamics simulations. The temperature dependences of dynamic properties during the liquid–glass transition are investigated. Two relaxation processes are clearly observed near the glass transition temperature. The diffusivity deviates from the Arrhenius law after the melting temperature Tm and satisfies the power law before the dynamic singularity temperature Tc owing to the cage effect. The solid- and liquid-like atoms are defined according to the vibration characteristic of atoms. It is found that the solid-like atoms have higher local packing density, lower mobility and potential energy than the liquid-like ones. Based on the evolutions of solid- and liquid-like atoms, the atomic mechanism of dynamic liquid–glass transition is systematically elucidated, which is consistent with the potential energy landscape.

Kinetics of Relaxation at the Liquid-Glass Transition

1990 ◽  
Vol 205 ◽  
Author(s):  
Laurent J. Lewis
Keyword(s):  
Glass Transition ◽  
Liquid Glass ◽  
Realistic Model ◽  
Relaxation Mechanism ◽  
Relaxation Processes ◽  
Conformational Relaxation ◽  
Atomic Transport ◽  
Dynamics Simulations ◽  
Two Stages ◽  
Kinetics Of

AbstractWe use molecular-dynamics simulations to investigate relaxation processes near the liquid-glass transition for a realistic model of the metal-metalloid system Ni80P20. We find that relaxation proceeds in two stages, excluding phonons: fast (or conformational) relaxation, related to local rearrangements of atoms, and slow relaxation, connected with atomic transport, i.e. diffusion. These processes are usually referred to as β and α, respectively. Our simulations show that diffusion exists even in the glass state, where it proceeds mostly by jumps, in contrast to the liquid phase where it is continuous. This relaxation mechanism is well described by a stretched exponential (Kohlrausch) law, in accord with recent modecoupling theories for supercooled liquids. The fast relaxation regime, on the other hand, does not appear to be well described by the theory.

Catalysis with a Skip: Dynamically Coupled Addition, Proton Transfer, and Elimination During Au- and Pd-Catalyzed Diol Cyclization

2021 ◽  
Author(s):  
Matthew Teynor ◽  
Windsor Scott ◽  
Daniel Ess
Keyword(s):  
Potential Energy ◽  
Proton Transfer ◽  
Energy Landscape ◽  
Cyclization Reactions ◽  
Potential Energy Landscape ◽  
Water Elimination ◽  
Catalytic Intermediates ◽  
Pd Complexes ◽  
Dynamics Simulations ◽  
Step Mechanism

Au and Pd complexes have emerged as highly effective π-bond cyclization catalysts to construct heterocycles. These cyclization reactions are generally proposed to proceed through multi-step addition-elimination mechanisms involving Au- or Pd-alkyl intermediates. For Au- and Pd-catalyzed allylic diol cyclization, while the DFT potential energy surface landscapes show a stepwise sequence of alkoxylation π-addition, proton transfer, and water elimination, quasiclassical direct dynamics simulations reveal new dynamical mechanisms that depend on the metal center. For Au, trajectories reveal that after π-addition the Au-alkyl intermediate is always skipped because addition is dynamically coupled with proton transfer and water elimination. In contrast, for Pd catalysis, due to differences in the potential-energy landscape shape, only about half of trajectories show Pd-alkyl intermediate skipping. The other half of the trajectories show the traditional two-step mechanism with the intervening Pd-alkyl intermediate. Overall, this work reveals that interpretation of a DFT potential-energy landscape can be insufficient to understand catalytic intermediates and mechanisms and that atomic momenta through dynamics simulations is needed to determine if an intermediate is genuinely part of a catalytic cycle.<br>

TWO-STATE STRUCTURE OF NANOMETER-SIZED Cu PARTICLES

2008 ◽  
Vol 07 (02n03) ◽  
pp. 137-150
Author(s):  
GIUSEPPE MANAI ◽  
FRANCESCO DELOGU
Keyword(s):  
Surface Layer ◽  
Melting Point ◽  
Potential Energy ◽  
Dynamic Properties ◽  
Bulk Liquid ◽  
Bulk Solid ◽  
Radial Profiles ◽  
Atomic Species ◽  
Dynamics Simulations ◽  
Internal Domain

Molecular dynamics simulations have been employed to investigate the static and dynamic properties of unsupported spherical Cu particles with size ranging between 1 and 10 nm. The potential energy, the structural arrangement, and the mobility of atomic species were studied for each nanometer-sized particle within the temperature range between 300 K and the melting point. Two distinct regions, namely an internal domain and a surface layer, can be identified within each nanoparticle on the basis of the radial profiles of such quantities. The atomic species belonging to the interior of the particle display a bulk-like behavior. By contrast, the surface layer is characterized by an excess potential energy associated with a disordered structure. At relatively low temperatures, the surface atoms possess structural and energetic features intermediate between the ones of a superheated bulk solid and of an undercooled bulk liquid. Pre-melting processes at the surface are also evident at temperatures close to the melting point. The nanometer-sized particles can be thus regarded as heterogeneous two-state systems consisting of roughly distinguishable bulk-like and surface regions.

Catalysis with a Skip: Dynamically Coupled Addition, Proton Transfer, and Elimination During Au- and Pd-Catalyzed Diol Cyclization

2021 ◽  
Author(s):  
Matthew Teynor ◽  
Windsor Scott ◽  
Daniel Ess
Keyword(s):  
Potential Energy ◽  
Proton Transfer ◽  
Energy Landscape ◽  
Cyclization Reactions ◽  
Potential Energy Landscape ◽  
Water Elimination ◽  
Catalytic Intermediates ◽  
Pd Complexes ◽  
Dynamics Simulations ◽  
Step Mechanism

Au and Pd complexes have emerged as highly effective π-bond cyclization catalysts to construct heterocycles. These cyclization reactions are generally proposed to proceed through multi-step addition-elimination mechanisms involving Au- or Pd-alkyl intermediates. For Au- and Pd-catalyzed allylic diol cyclization, while the DFT potential energy surface landscapes show a stepwise sequence of alkoxylation π-addition, proton transfer, and water elimination, quasiclassical direct dynamics simulations reveal new dynamical mechanisms that depend on the metal center. For Au, trajectories reveal that after π-addition the Au-alkyl intermediate is always skipped because addition is dynamically coupled with proton transfer and water elimination. In contrast, for Pd catalysis, due to differences in the potential-energy landscape shape, only about half of trajectories show Pd-alkyl intermediate skipping. The other half of the trajectories show the traditional two-step mechanism with the intervening Pd-alkyl intermediate. Overall, this work reveals that interpretation of a DFT potential-energy landscape can be insufficient to understand catalytic intermediates and mechanisms and that atomic momenta through dynamics simulations is needed to determine if an intermediate is genuinely part of a catalytic cycle.<br>

scholarly journals The Significance of the Amorphous Potential Energy Landscape for Dictating Glassy Dynamics and Driving Solid-State Crystallisation

2017 ◽  
Author(s):  
Michael T. Ruggiero ◽  
Marcin Krynski ◽  
Eric Ofosu Kissi ◽  
Juraj Sibik ◽  
Daniel Markl ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Glass Transition ◽  
Potential Energy ◽  
Ab Initio Molecular Dynamics ◽  
Vast Number ◽  
Disordered Solids ◽  
Fundamental Factor ◽  
Molecular Features ◽  
Potential Energy Landscape ◽  
Terahertz Pulses

<div> <div> <div> <p>The fundamental origins surrounding the dynamics of disordered solids near their characteristic glass transitions continue to be fiercely debated, even though a vast number of materials can form amorphous solids, including small-molecule organic, inorganic, covalent, metallic, and even large biological systems. The glass-transition temperature, Tg, can be readily detected by a diverse set of techniques, but given that these measurement modalities probe vastly different processes, there has been significant debate regarding the question of why Tg can be detected across all of them. Here we show clear experimental and computational evidence in support of a theory that proposes that the shape and structure of the potential-energy surface (PES) is the fundamental factor underlying the glass-transition processes, regardless of the frequency that experimental methods probe. Whilst this has been proposed previously, we demonstrate, using ab initio molecular-dynamics (AIMD) simulations, that it is of critical importance to carefully consider the complete PES – both the intra-molecular and inter-molecular features – in order to fully un- derstand the entire range of atomic-dynamical processes in disordered solids. Finally, we show that it is possible to utilise this dependence to directly manipulate and harness amorphous dynamics in order to control the behaviour of such solids by using high-powered terahertz pulses to induce crystallisation and preferential crystal-polymorph growth in glasses. Combined, these findings provide direct evidence that the PES landscape, and the corresponding energy barriers, are the ultimate controlling feature behind the atomic and molecular dynamics of disordered solids, regardless of the frequency at which they occur. </p> </div> </div> </div>

scholarly journals Cooling under Applied Stress Rejuvenates Amorphous Alloys and Enhances Their Ductility

Metals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 67
Author(s):  
Nikolai V. Priezjev
Keyword(s):  
Glass Transition ◽  
Tensile Stress ◽  
Potential Energy ◽  
Applied Stress ◽  
Three Dimensional ◽  
Tensile Tests ◽  
Maximum Tensile Stress ◽  
Amorphous Structure ◽  
Glass Transition Point ◽  
Dynamics Simulations

The effect of tensile stress applied during cooling of binary glasses on the potential energy states and mechanical properties is investigated using molecular dynamics simulations. We study the three-dimensional binary mixture that was first annealed near the glass transition temperature and then rapidly cooled under tension into the glass phase. It is found that at larger values of applied stress, the liquid glass former freezes under higher strain and its potential energy is enhanced. For a fixed cooling rate, the maximum tensile stress that can be applied during cooling is reduced upon increasing initial temperature above the glass transition point. We also show that the amorphous structure of rejuvenated glasses is characterized by an increase in the number of contacts between smaller type atoms. Furthermore, the results of tensile tests demonstrate that the elastic modulus and the peak value of the stress overshoot are reduced in glasses prepared at larger applied stresses and higher initial temperatures, thus indicating enhanced ductility. These findings might be useful for the development of processing and fabrication methods to improve plasticity of bulk metallic glasses.

scholarly journals The Significance of the Amorphous Potential Energy Landscape for Dictating Glassy Dynamics and Driving Solid-State Crystallisation

2017 ◽  
Author(s):  
Michael T. Ruggiero ◽  
Marcin Krynski ◽  
Eric Ofosu Kissi ◽  
Juraj Sibik ◽  
Daniel Markl ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Glass Transition ◽  
Potential Energy ◽  
Ab Initio Molecular Dynamics ◽  
Vast Number ◽  
Disordered Solids ◽  
Fundamental Factor ◽  
Molecular Features ◽  
Potential Energy Landscape ◽  
Terahertz Pulses

<div> <div> <div> <p>The fundamental origins surrounding the dynamics of disordered solids near their characteristic glass transitions continue to be fiercely debated, even though a vast number of materials can form amorphous solids, including small-molecule organic, inorganic, covalent, metallic, and even large biological systems. The glass-transition temperature, Tg, can be readily detected by a diverse set of techniques, but given that these measurement modalities probe vastly different processes, there has been significant debate regarding the question of why Tg can be detected across all of them. Here we show clear experimental and computational evidence in support of a theory that proposes that the shape and structure of the potential-energy surface (PES) is the fundamental factor underlying the glass-transition processes, regardless of the frequency that experimental methods probe. Whilst this has been proposed previously, we demonstrate, using ab initio molecular-dynamics (AIMD) simulations, that it is of critical importance to carefully consider the complete PES – both the intra-molecular and inter-molecular features – in order to fully un- derstand the entire range of atomic-dynamical processes in disordered solids. Finally, we show that it is possible to utilise this dependence to directly manipulate and harness amorphous dynamics in order to control the behaviour of such solids by using high-powered terahertz pulses to induce crystallisation and preferential crystal-polymorph growth in glasses. Combined, these findings provide direct evidence that the PES landscape, and the corresponding energy barriers, are the ultimate controlling feature behind the atomic and molecular dynamics of disordered solids, regardless of the frequency at which they occur. </p> </div> </div> </div>

scholarly journals The Significance of the Amorphous Potential Energy Landscape for Dictating Glassy Dynamics and Driving Solid-State Crystallisation

2017 ◽  
Author(s):  
Michael T. Ruggiero ◽  
Marcin Krynski ◽  
Eric Ofosu Kissi ◽  
Juraj Sibik ◽  
Daniel Markl ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Glass Transition ◽  
Potential Energy ◽  
Ab Initio Molecular Dynamics ◽  
Vast Number ◽  
Disordered Solids ◽  
Fundamental Factor ◽  
Molecular Features ◽  
Potential Energy Landscape ◽  
Terahertz Pulses

<div> <div> <div> <p>The fundamental origins surrounding the dynamics of disordered solids near their characteristic glass transitions continue to be fiercely debated, even though a vast number of materials can form amorphous solids, including small-molecule organic, inorganic, covalent, metallic, and even large biological systems. The glass-transition temperature, Tg, can be readily detected by a diverse set of techniques, but given that these measurement modalities probe vastly different processes, there has been significant debate regarding the question of why Tg can be detected across all of them. Here we show clear experimental and computational evidence in support of a theory that proposes that the shape and structure of the potential-energy surface (PES) is the fundamental factor underlying the glass-transition processes, regardless of the frequency that experimental methods probe. Whilst this has been proposed previously, we demonstrate, using ab initio molecular-dynamics (AIMD) simulations, that it is of critical importance to carefully consider the complete PES – both the intra-molecular and inter-molecular features – in order to fully un- derstand the entire range of atomic-dynamical processes in disordered solids. Finally, we show that it is possible to utilise this dependence to directly manipulate and harness amorphous dynamics in order to control the behaviour of such solids by using high-powered terahertz pulses to induce crystallisation and preferential crystal-polymorph growth in glasses. Combined, these findings provide direct evidence that the PES landscape, and the corresponding energy barriers, are the ultimate controlling feature behind the atomic and molecular dynamics of disordered solids, regardless of the frequency at which they occur. </p> </div> </div> </div>

scholarly journals The significance of the amorphous potential energy landscape for dictating glassy dynamics and driving solid-state crystallisation

2017 ◽  
Vol 19 (44) ◽  
pp. 30039-30047 ◽  
Author(s):  
Michael T. Ruggiero ◽  
Marcin Krynski ◽  
Eric Ofosu Kissi ◽  
Juraj Sibik ◽  
Daniel Markl ◽  
...  
Keyword(s):  
Glass Transition ◽  
Solid State ◽  
Potential Energy ◽  
Energy Landscape ◽  
Glassy Dynamics ◽  
Fundamental Factor ◽  
Potential Energy Landscape

We show clear evidence for a theory proposing that the shape and structure of the PES is the fundamental factor underlying the dynamics at temperatures below the glass transition.

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