ORCID Profile
0000-0002-8871-5013
Current Organisation
University of Sydney
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Statistical Mechanics | Theoretical and Computational Chemistry | Theory Of Materials | Statistical Mechanics in Chemistry | Condensed Matter Physics—Structural Properties | Macromolecular and Materials Chemistry | Theoretical And Computational Chemistry Not Elsewhere Classified | Mathematical Physics | Mechanical Engineering | Polymers | Mechanical Engineering |
Chemical sciences | Expanding Knowledge in the Chemical Sciences | Expanding Knowledge in the Physical Sciences | Other | Plastics in primary forms | Metals (composites, coatings, bonding, etc.) | Lubricants
Publisher: AIP Publishing
Date: 10-2004
DOI: 10.1063/1.1797074
Abstract: Clusters of hard sphere ions with sufficient size asymmetry to stabilize a tetrahedral structure in the bulk are found to exhibit trivalent polyhedral ground states in clusters of up to roughly 200 ions. The map of cluster ground state structures over the space of cluster size and ion asymmetry is presented.
Publisher: AIP Publishing
Date: 15-02-1984
DOI: 10.1063/1.446864
Abstract: We construct a molecular theory for the homogeneous nucleation of crystals from pure liquids by combining an order parameter theory of freezing with a square gradient approximation for the nonlocal dependence of free energy on density. We show the results of our theory for the free energy, radius, and shape of crystal nuclei as a function of supercooling, and compare with the conventional nucleation theory based on the capillarity approximation. We argue that the simple picture given by the conventional approach is qualitatively reasonable, although calculated values of the liquid–solid surface free energy may be inaccurate. We point out some of the limitations of our approach and stress the need for additional structural data on supercooled liquids.
Publisher: American Physical Society (APS)
Date: 10-05-2006
Publisher: American Physical Society (APS)
Date: 05-1986
Publisher: IOP Publishing
Date: 17-02-2000
Publisher: AIP Publishing
Date: 22-06-1999
DOI: 10.1063/1.479155
Abstract: The effect on phase behavior of adding flexible terminal chains to a rigid core is examined with a simple model particle. It is discovered that two types of smectic phase appear in the phase diagram, a smectic A phase and a smectic C phase. The detailed nature of these phases is examined, as is the type of transition that takes place and the particle properties that drive the transition.
Publisher: American Physical Society (APS)
Date: 08-1997
Publisher: Proceedings of the National Academy of Sciences
Date: 02-10-2019
Publisher: AIP Publishing
Date: 06-11-2007
DOI: 10.1063/1.2799186
Abstract: We demonstrate that the linear response theory of interface friction presented by Bocquet and Barrat [Phys. Rev. E 49, 3079 (1994)] results in a friction coefficient that is not an intrinsic property of the interface and thus does not correspond to the actual interfacial friction coefficient. We point out that this previous derivation includes an unsubstantiated identification of the velocity field in the nonuniform system with the perturbation applied to the equations of the motion. We present an alternative equilibrium theory of the friction associated with the confined fluid and show how this friction is related to the intrinsic interfacial friction.
Publisher: AIP Publishing
Date: 09-1993
DOI: 10.1063/1.466122
Abstract: The microscopic dynamics of freezing and melting at the 100 and 111 surfaces of a simple cubic crystal are examined. The kinetics are described using coupled Landau–Ginzberg equations based on a mean field approximation of the face centered cubic lattice gas with nearest and next nearest neighbor interactions. Anomalous large structural fluctuations are found at the equilibrium 100 surface, a result of the weak coupling between close packed 100 planes. This feature also gives rise to a large anisotropy in interface mobilities on freezing with the 100 surface mobility vanishing unless fluctuations or longer range interactions are included. The interface mobilities during melting are found to be substantially larger than those found during freezing for both surfaces, a result attributed to the asymmetry between crystal and liquid in the free energy functional.
Publisher: AIP Publishing
Date: 27-01-2006
DOI: 10.1063/1.2145762
Abstract: We present a method for the direct calculation at equilibrium of the shear viscosity and thermal conductivity over distances as short as one molecular diameter. The method is directly applicable to the calculation of viscosity and thermal conductivity in inhomogeneities such as the interface between coexisting phases. The method makes use of a novel extension of our recently developed boundary fluctuation theory.
Publisher: IOP Publishing
Date: 25-11-2005
Publisher: American Physical Society (APS)
Date: 08-01-2014
Publisher: Elsevier BV
Date: 09-2018
Publisher: Elsevier BV
Date: 08-1998
Publisher: American Physical Society (APS)
Date: 22-01-2003
Publisher: American Physical Society (APS)
Date: 30-05-2013
Publisher: AIP Publishing
Date: 20-04-2021
DOI: 10.1063/5.0049009
Abstract: We calculate the degree to which the final structure of the local groundstate in a liquid is a function of the strength of a perturbing potential applied during energy minimization. This structural susceptibility is shown to correlate well with the observed tendency of the liquid adjacent to a crystal interface to exhibit a crystalline groundstate, a feature that has been strongly linked to the observation of ultra-fast crystal growth in pure metals and ionic melts. It is shown that the structural susceptibility increases dramatically as the interaction potential between atoms is softened.
Publisher: American Chemical Society (ACS)
Date: 14-02-2018
Abstract: The kinetics of dissolution of an amorphous solid is studied using a simple model of a glass that captures with reasonable accuracy the dynamic heterogeneities associated with the relaxation of an amorphous material at low temperatures. The intrinsic dissolution rate is shown to be proportional to the concentration of surface particles kinetically able to exchange with the solvent, independent of temperature or the thermal history of the glass. The morphology of the dissolving surface is described, and the possibility of using surface etching to image dynamic heterogeneities is explored.
Publisher: American Physical Society (APS)
Date: 09-1997
Publisher: American Physical Society (APS)
Date: 26-05-2006
Publisher: American Physical Society (APS)
Date: 05-1999
Abstract: The structural and thermodynamic properties of a two-dimensional binary mixture of soft discs are reported over a range of temperatures down to large supercoolings using constant NPT molecular dynamics simulations. It is shown that the four orders of magnitude increase in the structural relaxation time is not accompanied by any significant increase in translational or orientational order. The phase diagram, calculated in the temperature/composition plane using thermodynamic integration, exhibits a deep eutectic point that is responsible for stabilizing the amorphous state. Voronoi analysis of the low-temperature ground state reveals a structure characterized by a network of linear arrays of fivefold and sevenfold sites. The heat capacity C(P) exhibits an asymmetric peak with a maximum at T(*)=0.55. It is argued that the initial rapid drop in C(P) for T*<0.55 is an equilibrium result and, hence, the peak in the heat capacity corresponds to the existence of an "enthalpy gap" with a characteristic temperature of T* approximately 0.35. This gap results from a minimum volume change associated with an anharmonic fluctuation.
Publisher: AIP Publishing
Date: 19-11-2009
DOI: 10.1063/1.3265983
Abstract: Using computer simulations, we show that the localized low frequency normal modes of a configuration in a supercooled liquid are strongly correlated with the irreversible structural reorganization of the particles within that configuration. Establishing this correlation constitutes the identification of the aspect of a configuration that determines the heterogeneity of the subsequent motion. We demonstrate that the spatial distribution of the summation over the soft local modes can persist in spite of particle reorganization that produces significant changes in in idual modes. Along with spatial localization, the persistent influence of soft modes in particle relaxation results in anisotropy in the displacements of mobile particles over the time scale referred to as β-relaxation.
Publisher: Proceedings of the National Academy of Sciences
Date: 08-09-2009
Abstract: We show how the spatial character of unconstrained motion in a network of bonds can be directly inferred from the topological arrangement of constraints. Relaxation time scales of these soft modes are determined, and from this information we generate spatial maps of the heterogeneous distribution of relaxation times in the disordered network. We show that the nature of the dynamic heterogeneity and its sensitivity to changes in bond configuration depends dramatically on the proximity of the system to the rigidity percolation point.
Publisher: AIP Publishing
Date: 15-12-1985
DOI: 10.1063/1.449579
Abstract: The quantum theory of the pressure dependence of collision induced intersystem crossing is developed in the impact limit where collision times are short compared to time scales for molecular decay. A basic model is introduced which contains singlet–triplet intramolecular couplings and collisional processes that correspond in a pure spin basis to dephasing of singlet–triplet and triplet–triplet coherences and to triplet state population decay. Expressions are derived for the ratio of the emission yield at zero pressure ided by that at pressure p in the separate limits of low triplet level density and of short triplet–triplet coherence lifetimes. The first order corrections to the latter case are found to be negligible over a wide range of pressure and molecular parameters. The theory shows that pressure saturation of collision induced intersystem crossing emerges from a competition between dephasing and population decay processes induced by the collider. A strong sensitivity is exhibited to the minimum zeroth order singlet–triplet splitting.
Publisher: Springer Science and Business Media LLC
Date: 02-2002
DOI: 10.1038/4151008A
Publisher: AIP Publishing
Date: 23-05-2008
DOI: 10.1063/1.2925797
Publisher: American Chemical Society (ACS)
Date: 05-04-2011
DOI: 10.1021/JP110975Y
Abstract: We report on the glass-forming abilities of the homologous series 1,2-diphenylcyclo-butene, pentene, hexene and heptene-a series that retains the cis-phenyl configuration characteristic of the well-studied glass former, o-terphenyl. We find that the glass-forming ability shows a sharp maximum for the six-membered ring and demonstrate that this trend in glass-forming ability is a consequence of a maximum, for the 1,2-diphenylcyclohexene, of the reduced glass transition temperature T(g)/T(m). Since the nonmonotonic trend in T(g)/T(m) is entirely due to variations in T(m), we conclude that the design target for maximizing the glass-forming ability across an homologous series should focus on the crystal stability and the factors that determine it.
Publisher: AIP Publishing
Date: 28-09-2021
DOI: 10.1063/5.0061042
Abstract: We introduce a minimal model of solid-forming anisotropic molecules that displays, in thermal equilibrium, surface orientational order without bulk orientational order. The model reproduces the nonequilibrium behavior of recent experiments in which a bulk nonequilibrium structure grown by deposition contains regions of orientational order characteristic of the surface equilibrium. This order is deposited, in general, in a nonuniform way because of the emergence of a growth-poisoning mechanism that causes equilibrated surfaces to grow slower than non-equilibrated surfaces. We use evolutionary methods to design oscillatory protocols able to grow nonequilibrium structures with uniform order, demonstrating the potential of protocol design for the fabrication of this class of materials.
Publisher: American Physical Society (APS)
Date: 05-10-2006
Publisher: AIP Publishing
Date: 25-05-2023
DOI: 10.1063/5.0150312
Abstract: We monitor the transformation of a liquid into an amorphous solid in simulations of a glass forming liquid by measuring the variation of a structural order parameter with either changing temperature or potential energy to establish the influence of the cooling rate on amorphous solidification. We show that the latter representation, unlike the former, exhibits no significant dependence on the cooling rate. This independence extends to the limit of instantaneous quenches, which we find can accurately reproduce the solidification observed during slow cooling. We conclude that amorphous solidification is an expression of the topography of the energy landscape and present the relevant topographic measures.
Publisher: AIP Publishing
Date: 03-02-2012
DOI: 10.1063/1.3681364
Abstract: The structure and available degrees of freedom of an amorphous configuration can determine the location of dynamic heterogeneities. In the same way, these features can also determine the directionality of the particle motion. In this paper we propose that directionality can be attributed to those particles that only participate in a single unconstrained motion. The consequences of this suggestion in terms of the spatial distribution of particles with high directionality are explored using a random bond model.
Publisher: AIP Publishing
Date: 23-12-2010
DOI: 10.1063/1.3511721
Abstract: The recent experimental fabrication of ultrastable glass films, via vapor deposition [Swallen et al., Science 315, 353 (2007)] and the observation of frontlike response to the annealing of these films [Swallen et al., Phys. Rev. Lett. 102, 065503 (2009)] have raised important questions about the possibility of manipulating the properties of glass films and addressing fundamental questions about kinetics and thermodynamics of amorphous materials. Central to both of these issues is the need to establish the essential physics that governs the formation of the ultrastable films and their subsequent response. In this paper, we demonstrate that a generic model of glassy dynamics can account for the formation of ultrastable films, the associated enhancement of relaxation rates by a factor of 105, the observation of frontlike response to temperature jumps and the temperature dependence of the front velocity.
Publisher: AIP Publishing
Date: 15-09-1991
DOI: 10.1063/1.461768
Abstract: Monte Carlo simulation data from the two-dimensional facilitated kinetic Ising model proposed by Fredrickson and Andersen is examined with the goal of understanding the processes responsible for the characteristic features of glassy dynamics. The spatial distribution of spin flip rates is found to be highly nonuniform with pockets of rapidly relaxing spins surrounded by kinetically locked domains. The slow relaxation of these latter domains, which gives rise to the characteristic long time tail of the linear response function, is due to the action of rare clusters of spins which are able to propagate their influence throughout the s le. An analytic expression is derived for the density of these active sites which is found to fully account for the non-Arrhenius temperature dependence of the relaxation time in this model. The consequences of these results for both theories and experiments in structural glasses are discussed.
Publisher: American Physical Society (APS)
Date: 18-05-1998
Publisher: AIP Publishing
Date: 15-09-1991
DOI: 10.1063/1.461769
Abstract: A measure of cooperativity in glassy liquids is defined in terms of the kinetic correlation length of relaxation at a surface. This length and its temperature dependence is measured for the facilitated kinetic Ising model with both free and pinned surfaces. A simple power law is found to describe the relationship between the kinetic correlation length and the bulk relaxation time over four decades of data.
Publisher: American Physical Society (APS)
Date: 09-1990
Publisher: Elsevier BV
Date: 11-2006
Publisher: AIP Publishing
Date: 22-11-1997
DOI: 10.1063/1.475011
Abstract: Time-delayed intensity cross correlation functions are used to analyze the structural relaxation of a two-dimensional liquid of soft disks as simulated using a molecular dynamics algorithm. The structural relaxation exhibits an increasing long time tail as the freezing transition is approached. A cross correlation function designed to select out only local hexagonal fluctuations is used to demonstrate explicitly that this slow relaxation arises from crystalline fluctuations. A theoretical treatment of the role of aperture size and cluster distribution in the scattering correlation functions is presented.
Publisher: AIP Publishing
Date: 03-1987
DOI: 10.1063/1.452044
Abstract: The way in which the velocity of a propagating interface determines the degree of surface disorder and the anisotropy of such interfacial velocities due to a crystalline lattice are examined using steady state solutions of the time dependent Landau–Ginzburg or Cahn–Hilliard equations. In the case of an interface described by two weakly coupled order parameters a ergence of the thickness of the surface disorder at a critical interfacial velocity is described. It is demonstrated that even for two surfaces with the same surface tension the growth rates may differ significantly due to a geometric factor arising from the underlying crystal lattice.
Publisher: American Chemical Society (ACS)
Date: 09-03-2004
DOI: 10.1021/JP037660L
Publisher: Informa UK Limited
Date: 04-2011
Publisher: AIP Publishing
Date: 12-06-2018
DOI: 10.1063/1.5025203
Abstract: In this paper, we compare the composition fluctuations and interaction potentials of a good metallic glass former, Cu50Zr50, and a poor glass former, Ni50Al50. The Bhatia-Thornton correlation functions are calculated. Motivated by the observation of chemical ordering at the NiAl surface, we derive a new property, R^cn(q), corresponding to the linear susceptibility of concentration to a perturbation in density. We present a direct comparison of the potentials for the two model alloys using a 2nd order density expansion, and establish that the one-body energy plays a crucial role in stabilizing the crystal relative to the liquid in both alloys but that the three-body contribution to the heat of fusion is significantly larger in NiAl than CuZr.
Publisher: American Physical Society (APS)
Date: 09-03-2010
Publisher: AIP Publishing
Date: 03-07-2012
DOI: 10.1063/1.4730912
Abstract: The persistence of shear stress fluctuations in viscous liquids is a direct consequence of the non-zero shear stress of the local potential minima which couples stress relaxation to transitions between inherent structures. In simulations of 2D and 3D glass forming mixtures, we calculate the distribution of this inherent shear stress and demonstrate that the variance is independent of temperature and obeys a power law in density. The inherent stress is shown to involve only long wavelength fluctuations, evidence of the central role of the static boundary conditions in determining the residual stress left after the minimization of the potential energy. A temperature Tη is defined to characterise the crossover from stress relaxation governed by binary collisions at high temperatures to low temperature relaxation dominated by the relaxation of the inherent stress. Tη is found to coincide with the breakdown of the Stokes-Einstein scaling of diffusion and viscosity.
Publisher: AIP Publishing
Date: 24-12-2015
DOI: 10.1063/1.4937952
Abstract: It is proposed that the rate of relaxation in a liquid is better described by the geometric mean of the van Hove distribution function, rather than the standard arithmetic mean used to obtain the mean squared displacement. The difference between the two means is shown to increase significantly with an increase in the non-Gaussian character of the displacement distribution. Preliminary results indicate that the geometric diffusion constant results in a substantial reduction of the deviation from Stokes-Einstein scaling.
Publisher: AIP Publishing
Date: 22-09-2006
DOI: 10.1063/1.2347705
Abstract: We propose a phenomenological model for shear-induced melting aimed at assisting the design of experimental studies of this phenomenon. For increasing strain rates, the model predicts the changes in liquid fraction and shear stress as a function of interfacial supercooling. We discuss the experimental conditions under which shear-induced melting could be observed in a range of materials.
Publisher: Informa UK Limited
Date: 20-04-1985
Publisher: American Physical Society (APS)
Date: 25-09-2020
Publisher: American Association for the Advancement of Science (AAAS)
Date: 18-03-2022
Abstract: The mechanical properties of crystals are controlled by the translational symmetry of their structures. But for glasses with a disordered structure, the link between the symmetry of local particle arrangements and stability is not well established. In this contribution, we provide experimental verification that the centrosymmetry of nearest-neighbor polyhedra in a glass strongly correlates with the local mechanical stability. We examine the distribution of local stability and local centrosymmetry in a glass during aging and deformation using microbeam x-ray scattering. These measurements reveal the underlying relationship between particle-level structure and larger-scale behavior and demonstrate that spatially connected, coordinated local transformations to lower symmetry structures are fundamental to these phenomena. While glassy structures lack obvious global symmetry breaking, local structural symmetry is a critical factor in predicting stability.
Publisher: American Physical Society (APS)
Date: 08-1995
Publisher: Elsevier BV
Date: 03-2009
Publisher: American Physical Society (APS)
Date: 30-03-2016
Publisher: AIP Publishing
Date: 03-1992
DOI: 10.1063/1.462864
Abstract: When a liquid crystallizes, both its structure and its average density change. The former represents a nonconserved, and the later a conserved, order parameter. Including convective flow in the fluid leads to coupled equations for average density and structural order parameter that resemble those for nonconserved order parameters, and that allow steady-state solutions. We use a simple square-gradient free-energy functional to explore the solutions to these equations and relate them to experiments and computer simulations for the crystallization of atomic fluids such as argon, silicon, sodium, and lead. The effect of the density change on freezing is predicted to be small in most cases.
Publisher: AIP Publishing
Date: 15-12-1996
DOI: 10.1063/1.472941
Abstract: The single particle dynamics of a 2D liquid made up of soft disks interacting by a repulsive r−12 potential are studied using molecular dynamics simulations. We find that mean squared particle displacement 〈Δr(t)2〉 behaves diffusively, i.e., increases linearly with time, within a time interval tc very much shorter than that required for structural relaxation. The non-Gaussian parameter α(t)=〈Δr4〉/2〈Δr2〉2−1, on the other hand, exhibits a significant peak at times considerably greater than tc and a subsequent slow decay. It is argued that the only picture of diffusion consistent with these results considers particles moving in a medium characterized by fluctuating local mobilities. This picture provides an explicit connection between structural fluctuations (as characterized by the local mobility) and single particle motion. The possibility of obtaining the width and lifetime of the distribution of local relaxation times from incoherent scattering is examined.
Publisher: American Physical Society (APS)
Date: 27-07-2012
Publisher: American Physical Society (APS)
Date: 31-01-2011
Publisher: AIP Publishing
Date: 08-03-2002
DOI: 10.1063/1.1446434
Abstract: Monte Carlo calculations of the specific heat of a model glass have been carried out to determine the thermodynamic consequences of the configurational constraints required to define a single glass state. Three different configurational constraints were employed. Using a cell model, we find a steady decrease in the heat capacity CV with increasing temperature indicating a significant anharmonic behavior in the soft disk glass. If, instead, we constrain the particle fluctuations to uncoupled instantaneous normal modes (INM’s), we find that the heat capacity is almost independent of temperature and equal to the harmonic value, even when the full anharmonic potential is used. To resolve this contradiction, we employ a tether constraint and find reasonable agreement with the cell model results. We conclude (i) that the harmonic behavior under the INM constraint is an artifact arising from the arbitrary restrictions on particle motions, and (ii) that the soft disk glass is an anharmonic solid with a heat capacity that decreases on heating along an isobar.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5SM00312A
Abstract: We investigate the connection between the geometry of Favoured Local Structures (FLS) in liquids and the associated liquid and solid properties.
Publisher: American Physical Society (APS)
Date: 06-07-1998
Publisher: AIP Publishing
Date: 03-08-2021
DOI: 10.1063/5.0060000
Abstract: At a macroscopic level, concepts such as “top spin,” “back spin,” and “rolling” are commonly used to describe the collision of balls and surfaces. Each term refers to an aspect of the coupling of rotational motion during the collision of a spherical particle with a planar surface. In this paper, we explore the mechanisms of energy transfer involving the collision of a rotating sphere and a surface using a model of frictional interactions developed for a granular material. We present explicit analytical treatments for the scattering and derive expressions for two important limiting classes: energy conserving collisions and collisions subject to rapid transverse dissipation.
Publisher: AIP Publishing
Date: 24-04-2020
DOI: 10.1063/5.0006527
Abstract: The crystal growth rates from a binary A50B50 Lennard-Jones liquid are calculated as a function of the variation of the interspecies interaction length σAB. At the crossover in stability between the CsCl and NaCl crystal phase, the growth rate slows down and exhibits a maximum in the activation energy for atomic attachment to the growing crystal. Using assignment theory to determine the size of the transformation displacement, we show that these trends can be explained in terms of the changes in the cage size of the liquid.
Publisher: AIP Publishing
Date: 18-07-2006
DOI: 10.1063/1.2216695
Abstract: Using molecular dynamics simulations, we show that dodecane films confined between amorphous surfaces at 300K retain liquid-like behavior down to film thicknesses of at least 1.8nm and possibly smaller. This is in stark contrast to the behavior of films confined between crystalline surfaces which show an abrupt transition to a very high viscosity state at a film thickness of 4nm. We show that it is the small increase in surface roughness in going from crystalline to amorphous walls, rather than the in-plane disorder, that is responsible for disrupting the crystalline bridges found in the crystal-confined films. The main consequences of the in-plane disorder are the removal of the orientational pinning of the local domain alignment and the reduction of the critical thickness at which the transition to film rigidity appears.
Publisher: Springer Science and Business Media LLC
Date: 28-04-2013
DOI: 10.1038/NMAT3631
Abstract: Our ability to exploit the benefits of metallic glasses depends on identifying alloys of high glass-forming ability (GFA). So far, the established empirical correlations of GFA (ref. ) are statistical guides at best and lack a microscopic rationale. Although simulations have the potential to provide this physical insight into the maximum crystallization rate, crystal nucleation is often too slow to be observed. In contrast, measuring the growth rate of a planar crystal surface represents an accessible route to understanding ordering kinetics. Here we use molecular dynamics simulations to show that the crystal growth rate for an important binary glass former, CuZr, is significantly slower than that of a poor glass former, NiAl. In accounting for this difference, we find that the crystal/liquid interface in NiAl exhibits a significantly greater width than that of CuZr. Our results suggest that the crystal/liquid interfacial structure exerts an important influence on the GFA of alloys.
Publisher: AIP Publishing
Date: 08-05-2007
DOI: 10.1063/1.2724819
Abstract: We consider the infinite hierarchy of local collective rearrangements on bond networks that preserves the valency of each atom and explicitly enumerate those involving 4, 5, and 6 particles. The only 4-particle rearrangement is identical to the Wooten-Winer-Weaire (WWW) mechanism. Each rearrangement mechanism is applied in a Monte Carlo (MC) algorithm in order to determine the rate at which it equilibrate a network and relax the structure at equilibrium. At low temperature the 4-particle mechanism provides the fastest relaxation rate but we find that there is a crossover with increasing temperature to 5-particle mechanisms.
Publisher: American Physical Society (APS)
Date: 17-06-2022
Publisher: AIP Publishing
Date: 02-02-2021
DOI: 10.1063/5.0033206
Abstract: Using computer simulations, we establish that the structure of a supercooled binary atomic liquid mixture consists of common neighbor structures similar to those found in the equilibrium crystal phase, a Laves structure. Despite the large accumulation of the crystal-like structure, we establish that the supercooled liquid represents a true metastable liquid and that liquid can “borrow” the crystal structure without being destabilized. We consider whether this feature might be the origin of all instances of liquids with a strongly favored local structure.
Publisher: AIP Publishing
Date: 21-11-2011
DOI: 10.1063/1.3662073
Abstract: It is proposed that the dynamic heterogeneities of an amorphous material are strongly correlated with the spatial distribution of unconstrained degrees of freedom in the associated network of mechanical constraints. This latter distribution is shown to depend sensitively on whether or not overconstraints are permitted in the constraint network. When overconstraints are avoided, relaxation is achieved with few bond rearrangements and the susceptibility χ4 increases monotonically with increasing constraint density, in contrast to the case of a random network. This behaviour is associated with the marginal stability of the isostatic rigid cluster as opposed to the more robust structures generated when redundant bonds are permitted.
Publisher: IOP Publishing
Date: 06-07-2000
Publisher: AIP Publishing
Date: 17-04-2007
DOI: 10.1063/1.2719192
Abstract: The use of the isoconfigurational ensemble to explore structure-dynamic correlations in supercooled liquids is examined. The statistical error of the dynamic propensity and its spatial distribution are determined. The authors present the spatial distribution of the particle non-Gaussian parameter as a measure of the intermittency with which particles exhibit their propensity for motion. The ensemble average of the direction of particle motion is introduced to establish the anisotropy of the dynamic propensity.
Publisher: Elsevier BV
Date: 10-2007
Publisher: AIP Publishing
Date: 08-02-1996
DOI: 10.1063/1.470932
Abstract: There is growing evidence to suggest that cooperativity in glasses is characterized by a spatial distribution of relaxation times. In this paper we examine the consequences of such inhomogeneities in the measurement of translational and rotational diffusion constants. We find that the decay of a concentration profile (the basis of transient grating experiments) is accelerated by the development of additional gradients parallel to the relaxation time gradients. This may account for recently observed differences in the variation of rotational and translational diffusion constants with viscosity below the glass transition temperature. The additional gradients may also provide the first direct means of examining the length scale associated with these inhomogeneities.
Publisher: IOP Publishing
Date: 27-04-2011
DOI: 10.1088/0953-8984/23/19/194103
Abstract: Algorithms to search for crystal structures that optimize some extensive property (energy, volume, etc) typically make use of random particle reorganizations in the context of one or more numerical techniques such as simulated annealing, genetic algorithms or biased random walks, applied to the coordinates of every particle in the unit cell, together with the cell angles and lengths. In this paper we describe the restriction of such searches to predefined isopointal sets, breaking the problem into countable sub-problems which exploit crystal symmetries to reduce the dimensionality of the search space. Applying this method to the search for maximally packed mixtures of hard spheres of two sizes, we demonstrate that the densest packed structures can be identified by searches within a couple of isopointal sets. For the A(2)B system, the densest known packings over the entire tested range 0.2 < r(A)/r(B) < 2.5, including some improvements on previous optima, can all be identified by searches within a single isopointal set. In the case of the AB composition, searches of two isopointal sets generate the densest packed structures over the radius ratio range 0.2 < r(A)/r(B) < 5.0.
Publisher: AIP Publishing
Date: 29-04-2004
DOI: 10.1063/1.1689642
Abstract: The lattice energies at zero temperature are calculated, using Lennard-Jones interactions, for a large number of crystal structures associated with ordered binary compounds. In units of the AA interaction length and strength (i.e., σAA=εAA=1.0) we examine the lowest energy structures, including coexisting phases, across the space of cross-species interactions 0.6⩽σAB⩽1.1 and 1.0⩽εAB⩽2.0. The remaining parameters σBB=0.88 and εBB=0.5 are chosen so that the parameter space studied includes the space of binary glass-forming alloys. In addition to some large unit cell structures such as Ni3P and PuBr3 appearing among the lowest lattice energies, a number of low-energy structures based on close-packed lattices are found that do not correspond to any experimentally observed crystals. The prevalence and stability of metastable crystal phases at the compositions AB, A2B, and A3B is examined.
Publisher: American Chemical Society (ACS)
Date: 23-01-2009
DOI: 10.1021/JP807254B
Abstract: We present a general algorithm for calculating the spatial variation of the shear viscosity and thermal conductivity through an equilibrium solid-liquid interface using the zero-flux version of the boundary fluctuation theory. In the case of an equilibrium interface between a high melting point Lennard-Jones solid and a low melting point Lennard-Jones liquid, we find that the transport coefficients deviate from the bulk values only in a narrow layer close to the interface. We observe a sliding friction of the liquid against the surface of the solid that increases with increased wetting of the solid by the liquid. The thermal conductivity, in contrast, is suppressed in the interfacial region, irrespective of how the liquid wets the solid.
Publisher: AIP Publishing
Date: 15-09-1995
DOI: 10.1063/1.470653
Abstract: The shear induced disordering transition as observed in a dilute suspension of charged colloidal particles is modeled using nonequilibrium Brownian dynamics simulations. We report both real space and reciprocal space representations of the structure and dynamics of the sequence of steady states found as the shear rate is increased. While reproducing the observed steady-state structures at low shear rates, the simulated system was found to follow a different path to disorder with increasing shear. We find that the disordering process involves the accumulation of interstitial-vacancy defects in the shearing crystal as the shear rate increases. The disordering transition is also shown to exhibit an anisotropic dependence on system size. These two observations are combined in a new picture of the shear induced disordering transition. In this model a nonequilibrium defect density, generated by the coupling of long-wavelength fluctuations with the shear flow, eventually results in a collective disordering similar to the process of defect-induced amorphization in atomic solids.
Publisher: AIP Publishing
Date: 23-08-2012
DOI: 10.1063/1.4747326
Abstract: Supercooled liquids and glasses are important for current and developing technologies. Here we provide perspective on recent progress in this field. The interpretation of supercooled liquid and glass properties in terms of the potential energy landscape is discussed. We explore the connections between amorphous structure, high frequency motions, molecular motion, structural relaxation, stability against crystallization, and material properties. Recent developments that may lead to new materials or new applications of existing materials are described.
Publisher: American Physical Society (APS)
Date: 15-08-2016
Publisher: American Physical Society (APS)
Date: 08-1996
Publisher: Springer Science and Business Media LLC
Date: 20-07-2008
DOI: 10.1038/NPHYS1025
Publisher: Informa UK Limited
Date: 05-07-2016
Publisher: AIP Publishing
Date: 03-01-2013
DOI: 10.1063/1.4772480
Abstract: The fabrication of ultra-stable glass films by vapour deposition and their subsequent front-like response to annealing are both manifestations of the enhancement of dynamics at the amorphous surface. We use the facilitated kinetic Ising model to model the behaviour of ultra-stable amorphous films when a coating is applied that suppresses the dynamics at the film surface. The consequences of this manipulation of the film include glass films that can be heated to temperatures in excess of the glass transition without transforming into the liquid, the possibility of direct visualization of the spatial distribution of intrinsic dynamic heterogeneities, and the possibility of using surface treatment to engineer relaxation of these glass films.
Publisher: IOP Publishing
Date: 12-08-2016
Publisher: American Chemical Society (ACS)
Date: 05-1992
DOI: 10.1021/J100189A024
Publisher: American Chemical Society (ACS)
Date: 14-06-2008
DOI: 10.1021/JP802912A
Abstract: A systematic survey is presented of the maximum packing fractions obtained by decorating the 28 uniform tilings of three-dimensional space with spheres of one size and then filling the interstices of these tilings, starting with the largest, with spheres of different sizes. A number of size ratios and structures are identified that have not, to date, been considered in problems involving the packing of spheres of different sizes.
Publisher: American Physical Society (APS)
Date: 16-12-2009
Publisher: Proceedings of the National Academy of Sciences
Date: 03-02-2020
Abstract: We demonstrate that an accurate estimation of the displacements associated with the transformation of liquid into crystal is necessary to explain the striking variations in the temperature dependence of the addition rate of liquid atoms to the growing crystal interface during freezing. An assignment algorithm, adapted from operations theory, is shown to provide a good estimate of these atomic displacements. As the assignment algorithm requires only initial and target locations, it is applicable to all forms of structural transformations. In resolving a fundamental feature of the kinetics of freezing, a phenomenon of central importance to material fabrication, this paper also provides the tools to open lines of research into the kinetics of structural transformation.
Publisher: American Chemical Society (ACS)
Date: 05-2023
Publisher: AIP Publishing
Date: 03-01-2006
DOI: 10.1063/1.2140274
Abstract: In this paper we present, for the first time, a linear-response theory of transport coefficients—shear viscosity and thermal conductivity—involving thermal, as opposed to mechanical, fields. The theory involves the explicit treatment of the boundaries and the constraints that are applied to them. Expressions for the shear viscosity and thermal conductivity are obtained in terms of the fluctuations at the boundaries of the variable conjugate to that which is constrained. We explain how the choice of ensemble, as defined by the boundary constraints, determines the form in which the transport coefficients are evaluated.
Publisher: AIP Publishing
Date: 24-05-2004
DOI: 10.1063/1.1751394
Abstract: The native structure of fast-folding proteins, albeit a deep local free-energy minimum, may involve a relatively small energetic penalty due to nonoptimal, though favorable, contacts between amino acid residues. The weak energetic frustration that such contacts represent varies among different proteins and may account for folding behavior not seen in unfrustrated models. Minimalist model proteins with heterogeneous contacts—as represented by lattice heteropolymers consisting of three types of monomers—also give rise to weak energetic frustration in their corresponding native structures, and the present study of their equilibrium and nonequilibrium properties reveals some of the breadth in their behavior. In order to capture this range within a detailed study of only a few proteins, four candidate protein structures (with their cognate sequences) have been selected according to a figure of merit called the winding index—a characteristic of the number of turns the protein winds about an axis. The temperature-dependent heat capacities reveal a high-temperature collapse transition, and an infrequently observed low-temperature rearrangement transition that arises because of the presence of weak energetic frustration. Simulation results motivate the definition of a new measure of folding affinity as a sequence-dependent free energy—a function of both a reduced stability gap and high accessibility to non-native structures—that correlates strongly with folding rates.
Publisher: AIP Publishing
Date: 19-05-2008
DOI: 10.1063/1.2911924
Abstract: We calculate viscosity and thermal conductivity in systems of Lennard–Jones particles consisting of coexisting solid and liquid with different interface wetting properties using the recently developed equilibrium boundary fluctuation theory. We compare the slip length and equivalent liquid length obtained from these calculations with those obtained from nonequilibrium molecular dynamics. The equilibrium and nonequilibrium calculations of the slip length and the sum of the thermal equivalent lengths are in good agreement. We conclude that for both interfacial properties, the nonequilibrium simulations were probing the linear response. The significant dependence of the intrinsic equivalence length on the interfacial temperature difference used to generate the thermal gradient is explained as a consequence of the different thermodynamic states of the two interfaces.
Publisher: AIP Publishing
Date: 22-05-2001
DOI: 10.1063/1.1368403
Abstract: A theoretical study is presented on the kinetics of crystallization of a colloidal suspension in a fixed volume based upon the use of time dependent density functional theory incorporating conserved particle and nonconserved structure dynamics. This is a continuation of previous work done with conserved particle dynamics alone. The constraints of fixed number and volume lead to nonuniform solutions to the time independent equations of motion. One of the nonuniform solutions is found to have the minimum free energy and is identified as the stable equilibrium coexistence of crystalline and disordered suspension. Numerical integration is used to follow the time dependent motion of a range of initial crystallites. A broadband of stationary states, additional to those identified analytically, are located by the numerical integration. We show that these solutions arise from pinning induced by the discretization of space. The normal and tangential osmotic pressure fields are given and the growing crystallite is shown to be isolated from the higher pressure of the surrounding disordered suspension by the nonequilibrium depletion zone that surrounds it. These results are compared with recent light scattering studies.
Publisher: Elsevier BV
Date: 11-1986
DOI: 10.1016/0022-2836(86)90371-2
Abstract: The structure of poplar plastocyanin in the reduced (CuI) state has been determined and refined, using counter data recorded from crystals at pH 3.8, 4.4, 5.1, 5.9, 7.0 and 7.8 (resolution 1.9 A, 1.9 A, 2.05 A, 1.7 A, 1.8 A and 2.15 A the final residual R value was 0.15, 0.15, 0.16, 0.17, 0.16 and 0.15, respectively). The molecular and crystal structure of the protein is substantially the same in the reduced state as in the oxidized state. The refinements of the structures of the six forms of the reduced protein could therefore be commenced with a model derived from the known structure of CuII-plastocyanin. The refinements were made by reciprocal space least-squares calculations interspersed with inspections of electron-density difference maps. Precautions were taken to minimize any bias of the results of the refinements in the direction of the starting model. The most significant differences among the structures of the reduced protein at the six pH values, or between them and the structure of the oxidized protein, are concentrated at the Cu site. In the reduced protein at high pH (pH 7.8), the CuI atom is co-ordinated by the N delta(imidazole) atoms of His37 and His87, the S gamma(thiolate) atom of Cys84, and the S delta(thioether) atom of Met92, just as in CuII-plastocyanin. The distorted tetrahedral geometry and the unusually long Cu-S(Met92) bond are retained. The only effects of the change in oxidation state are a lengthening of the two Cu-N(His) bonds by about 0.1 A, and small changes in two bond angles involving the Cu-S(Cys) bond. The high-pH form of reduced plastocyanin accordingly meets all the requirements for efficient electron transfer. As the pH is lowered, the Cu atom and the four Cu-binding protein side-chains appear to undergo small but concerted movements in relation to the rest of the molecule. At low pH (pH 3.8), the CuI atom is trigonally co-ordinated by N delta(His37), S gamma(Cys84) and S delta(Met92). The fourth Cu-ligand bond is broken, the Cu atom making only a van der Waals' contact with the imidazole ring of His87. The trigonal geometry of the Cu atom strongly favours CuI, so that this form of the protein should be redox-inactive. This is known to be the case.(ABSTRACT TRUNCATED AT 400 WORDS)
Publisher: American Physical Society (APS)
Date: 19-04-2016
Publisher: Informa UK Limited
Date: 22-05-2015
Publisher: American Physical Society (APS)
Date: 22-06-2005
Publisher: AIP Publishing
Date: 24-03-2016
DOI: 10.1063/1.4944620
Abstract: Simulation studies of the atomic shear stress in the local potential energy minima (inherent structures) are reported for binary liquid mixtures in 2D and 3D. These inherent structure stresses are fundamental to slow stress relaxation and high viscosity in supercooled liquids. We find that the atomic shear stress in the inherent structures (IS’s) of both liquids at rest exhibits slowly decaying anisotropic correlations. We show that the stress correlations contribute significantly to the variance of the total shear stress of the IS configurations and consider the origins of the anisotropy and spatial extent of the stress correlations.
Publisher: AIP Publishing
Date: 13-12-2011
DOI: 10.1063/1.3666010
Abstract: Relaxation of the additivity condition on the interaction length between unlike species in a binary mixture of soft disks opens up a rich variety of structures in both crystal and amorphous states with an associated erse range of relaxation dynamics. We report on MD simulation studies of binary soft disks with negative deviations from additivity that include evidence of accumulation of crystal-like structures in metastable liquids prior to crystallization and the occurrence of a liquid to random-tiling transition.
Publisher: American Physical Society (APS)
Date: 22-05-2003
Publisher: American Physical Society (APS)
Date: 07-1996
Publisher: American Physical Society (APS)
Date: 12-1993
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 06-2018
Publisher: American Chemical Society (ACS)
Date: 02-1983
DOI: 10.1021/JA00342A008
Publisher: AIP Publishing
Date: 15-08-2001
DOI: 10.1063/1.1387039
Abstract: Using classical dynamics simulations, we model the long-lived structural effect of ultraviolet irradiation on amorphous silica. We find a significant increase in density of a model of amorphous silica following localized energy deposition, in agreement with experimental observation. We present evidence that this densification arises as a result of the rapid local cooling that follows irradiation. Similar high density forms of amorphous silica are found following fast quenches of bulk s les. In support of this proposal we demonstrate that very rapidly quenched silica undergoes dilation, rather than compaction, on irradiation.
Publisher: AIP Publishing
Date: 15-03-2011
DOI: 10.1063/1.3559153
Abstract: Crystallization is observed during microsecond long molecular dynamics simulations of bent trimers, a molecular model proposed by Lewis and Wahnström for ortho-terphenyl. In the crystal, the three spheres that make up the rigid molecule sit near sites of a body centered cubic lattice. The trimer bond angle is almost optimal for this structure. The crystal exhibits orientational disorder with the molecules aligned randomly along the three Cartesian axis, i.e., cubatic orientational order. The rotational and translational mobilities exhibit only modest decreases on crystallization, by factors of 10 and 3, respectively. The rotational relaxation does change from Debye-like in the liquid to large angle jumps in the crystal. We consider the origin of the superior glass forming ability of the trimer over the monatomic liquid.
Publisher: AIP Publishing
Date: 13-02-2003
DOI: 10.1063/1.1540091
Abstract: The coexistence between a strained crystal and its shearing melt is studied using nonequilibrium molecular dynamics simulations of Lennard-Jones particles. The coexistence is found to be independent of initial conditions, boundary effects, and the details of the thermostat. The nonequilibrium phase diagram is presented. The shear stress at coexistence is found to be significantly smaller than the yield stress of the crystal. It is demonstrated that there exists no physically reasonable prescription for a nonequilibrium analogue of chemical potential for the shearing liquid by which the coexistence could be attributed to an equality of chemical potentials between the two phases. We conclude that the nonequilibrium coexistence is determined by the stability of the interface.
Publisher: Springer Science and Business Media LLC
Date: 03-2006
DOI: 10.1038/NPHYS251
Publisher: American Chemical Society (ACS)
Date: 29-09-2011
DOI: 10.1021/JP205013W
Abstract: The time scales of crystallization of two model liquids, an atomic liquid and a molecular liquid of bent trimers originally introduced as a model of the glass the former o-terphenyl, are determined using molecular dynamics simulations. The molecular liquid is found to have a minimum crystallization time, on supercooling, that is 10(4) times larger than that of the atomic liquid. We present evidence that this enhanced glass-forming ability is due, in equal parts, to the slower dynamics and the larger crystal-liquid interfacial free energy in the molecular liquid.
Publisher: AIP Publishing
Date: 05-04-2012
DOI: 10.1063/1.3701617
Abstract: The role of the geometry of locally favoured structures in an equilibrium liquid is analyzed within a recently developed lattice model. The local geometry is shown to influence the liquid through the entropy and the associated density of states. We show that favoured local structures with low symmetry will, generally, incur a low entropy cost and, as a consequence, the liquid will exhibit a substantial accumulation of these low energy environments on cooling prior to the freezing transition.
Publisher: American Chemical Society (ACS)
Date: 29-04-2010
DOI: 10.1021/JP103375P
Publisher: AIP Publishing
Date: 15-05-1994
DOI: 10.1063/1.466855
Abstract: Dynamic Monte Carlo simulations are used to study the structure and dynamics of the 100 and the 111 crystal–liquid interfaces of the simple cubic phase in the face-centered-cubic lattice gas. At equilibrium the two surfaces are found to be distinguished only by the presence of strong surface-induced structural fluctuations at the close packed 100 surface. Away from equilibrium we find (i) the surfaces exhibit identical velocity vs temperature curves (ii) the interfacial velocity is a linear function of temperature (except at small supercoolings) (iii) the slope of velocity vs temperature in these linear regions is, for melting, double that seen in freezing and (iv) over a range of small supercoolings (less than 0.5% of the melting temperature) the interfacial velocity vanishes. The 111 surface is found to exhibit microfacets of 100 orientation over the entire temperature range studied. The asymmetry between freezing and melting dynamics and the origin of the stationary surface at small supercoolings are discussed in terms of the role of symmetry breaking fluctuations on the dynamics of interface motion.
Publisher: American Physical Society (APS)
Date: 24-09-2004
Publisher: American Chemical Society (ACS)
Date: 25-08-2007
DOI: 10.1021/JP0725578
Abstract: In this paper, we report on molecular dynamics simulation studies of thin dodecane films confined between mica surfaces. On confinement, the film undergoes a surface-mediated transition into a novel phase characterized by tetratic orientational order. The rheology of this ordered film is governed by slip planes and, at low shear rates, stick-slip behavior observable under steady shear rates. Melting of these films was observed either on heating or on exceeding a critical shear rate. Evidence is presented that this tetratic film is not the true equilibrium state rather, a state characterized by nematic order and very low viscosities is found to be more stable.
Publisher: MDPI AG
Date: 25-05-2023
Abstract: As a typical spinel ferrite, NiFe2O4 is suitable for use in gas sensors. Herein, we report the fabrication of porous, tremella-like NiFe2O4 assembled using porous, ultrathin nanosheets via the coordination of Ni2+ and Fe2+ with 1,4-phenylenediboronic acid. The optical band gap of the NiFe2O4 is estimated to be about 1.7 eV. Furthermore, the NiFe2O4 sensor annealed at 400 °C exhibits a low detection limit of 50 ppb, a fast response/recovery time (11.6 s/41.9 s to 10 ppm toluene), good reproducibility, and long-term stability at 220 °C. The suitable sensing performances can be attributed to the good catalytic activity of NiFe2O4 to toluene oxidation. Moreover, the ultrathin nanosheets with porous structures provide a large number of active sites to significantly favor the diffusion and adsorption/desorption of toluene molecules. This current work provides an insight into fabricating NiFe2O4 using 1,4-phenylenediboronic acid, which is promising for ppb-level toluene detection.
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C6SM02636B
Abstract: Novel crystal structures in binary atomic mixtures arise when the attractive well is wide enough to allow double occupancy by small particles. The resulting crystals consist of ordered packings of self assembled linear structures comprised of a cylindrical tube of large particles enclosing a close packed core of small particles that corresponds to a stacking of overlapping icosahedra. We show that the stability of these structures depends on two essential features of the spherically symmetric pairwise interactions: (i) a radius ratio between 0.414 and 0.588, and (ii) a width w of the attractive well in the interaction between unlike particles that satisfies w > σ
Publisher: AIP Publishing
Date: 03-08-2023
DOI: 10.1063/5.0164844
Abstract: A non-slip constraint between a particle and a wall is applied at the microscopic level of collision dynamics using the rough sphere model. We analyze the consequences of the translation–rotation coupling of a rough sphere confined between two parallel planar walls and establish that shearing the walls past each other (i) preferentially deposits energy into the rotational degree of freedom and (ii) results in a bounded oscillation of the energy of the confined particle.
Publisher: American Physical Society (APS)
Date: 11-02-2008
Publisher: AIP Publishing
Date: 22-09-1999
DOI: 10.1063/1.479804
Abstract: Molecular dynamics simulations are used to explore the spatial fluctuations associated with structural relaxation and particle transport in a supercooled binary mixture in two dimensions. The study includes (i) the characterization of heterogeneities in the local particle dynamics in terms of their length scale and lifetime, (ii) the relationship between local kinetics and local structure/composition, and (iii) preliminary identification of the principal collective motions involved in the long-time relaxation of the supercooled liquid.
Publisher: AIP Publishing
Date: 09-05-2003
DOI: 10.1063/1.1570401
Publisher: AIP Publishing
Date: 17-03-2009
DOI: 10.1063/1.3082008
Abstract: Insight into the efficient filling of space in systems of binary spheres is explored using bipyramids consisting of 3≤n≤8 tetrahedra sharing a common pair of spheres. Compact packings are sought in bipyramids consisting of larger hard spheres of unit radius and smaller hard spheres of radius 0.001≤R≤1. Seventy-seven distinct compact bipyramids are found. The number of distinct compact bipyramids increases with the number n of constituent tetrahedra. No compact bipyramids are found for R≥0.9473 and for 0.8493≥R≥0.7434. A topological instability eliminates compact packings for R≤0.1547. Pentagonal bipyramids cover a larger range in R than any other compact bipyramids studied.
Publisher: AIP Publishing
Date: 2000
DOI: 10.1063/1.480593
Abstract: The stability of nematic and smectic order in clusters of spherocylinders is examined via Monte Carlo simulations. A discontinuous isotropic–nematic transition is observed as the cluster size is varied through N=35. A continuous transition to smectic A order takes place from N=55 to N=200. The layered N=200 cluster exhibits a square cross section, an effect attributed to the increased orientational entropy of rods at surfaces of low curvature.
Publisher: American Physical Society (APS)
Date: 13-12-2006
Publisher: AIP Publishing
Date: 18-03-2019
DOI: 10.1063/1.5064531
Abstract: This paper presents a set of general strategies for the analysis of structure in amorphous materials and a general approach to assessing the utility of any selected structural description. Two measures of structure are defined, “ ersity” and “utility,” and applied to two model glass forming binary atomic alloys, Cu50Zr50 and a Lennard-Jones A80B20 mixture. We show that the change in ersity associated with selecting Voronoi structures with high localization or low energy, while real, is too weak to support claims that specific structures are the prime cause of these local physical properties. In addition, a new structure-free measure of incipient crystal-like organization in mixtures is introduced, suitable for cases where the stable crystal is a compound structure.
Publisher: AIP Publishing
Date: 15-03-1993
DOI: 10.1063/1.464961
Abstract: One approach to exploring the mechanisms which give rise to the characteristic distribution of relaxation times in a glass is to examine the correlation between this distribution and the spatial distribution of the relaxation rates. Detailed maps are presented of the spatial distribution of relaxation times in the facilitated kinetic Ising model of the structural glass transition. A statistical analysis of these spatial distributions leads to a set of correlation lengths associated with different aspects of the cooperative dynamics. One such length scale, ξ2, is found to be closely associated with the average relaxation time τL, the two quantities being related by a power law over 6 orders of magnitude variation in τL.
Publisher: AIP Publishing
Date: 10-1987
DOI: 10.1063/1.452919
Abstract: A theoretical treatment of a colloidal crystal undergoing shear flow is based on the assumption of small displacements of particles from the lattice sites of a deforming crystal. Long wavelength transverse modes are lified by the shearing solvent to produce fluctuations in adjacent particle separations which erge with the size of the crystal L as L1/2. These fluctuations are used with the Lindemann criterion to predict a shear melting transition in which the melting point depends on the size of the crystal. The consequences of this result for recent extensions of thermodynamics to systems under shear are discussed.
Publisher: AIP Publishing
Date: 12-1994
DOI: 10.1063/1.467956
Abstract: We report on dynamic Monte Carlo simulation studies of the extent and dynamics of structural fluctuations in the liquid phase of the fcc lattice gas with nearest-neighbor interactions. The structural relaxation exhibited nonexponential decay characterized by two time scales, a result in qualitative agreement with relaxation observed in colloidal suspensions. The time scale of the slow component increased more rapidly with decreasing temperature than that of the faster component. The origin of the slow component was traced to the presence of relatively long lived low-energy domains. The fluctuating cluster model was proposed to model the structural relaxation.
Publisher: American Physical Society (APS)
Date: 12-1995
Publisher: No publisher found
Date: 1996
DOI: 10.1063/1.471894
Publisher: American Physical Society (APS)
Date: 10-1992
Publisher: American Chemical Society (ACS)
Date: 09-08-2008
DOI: 10.1021/JP804953R
Abstract: This paper considers the homogeneous packing of binary hard spheres in an equimolar stoichiometry, and postulates the densest packing at each sphere size ratio. Monte Carlo simulated annealing optimizations are seeded with all known atomic inorganic crystal structures, and the search is performed within the degrees of freedom associated with each homogeneous AB structure type. Structures isopointal to the FeB structure type are found to have the highest packing fraction at all sphere size ratios. The optimized structures match or improve on the best previously demonstrated packings of this type, and show that compound structures can pack more densely than segregated close-packed structures at all radius ratios less than 0.62.
Publisher: Elsevier BV
Date: 06-2008
Publisher: AIP Publishing
Date: 08-04-2016
DOI: 10.1063/1.4944681
Abstract: A key property of glass forming alloys, the anomalously small volume difference with respect to the crystal, is shown to arise as a direct consequence of the soft repulsive potentials between metals. This feature of the inter-atomic potential is demonstrated to be responsible for a significant component of the glass forming ability of alloys due to the decrease in the enthalpy of fusion and the associated depression of the freezing point.
Publisher: AIP Publishing
Date: 08-10-1995
DOI: 10.1063/1.470441
Abstract: We describe a new layered phase, the discotic smectic, found in Monte Carlo simulations of hard parallelepipeds. This phase differs from the existing smectic A phase in that the shortest particle axis, rather than the longest, is aligned perpendicular to the layers. A range of particle shapes with dimensions varying from 5×1×1 (‘‘rods’’) to 5×1×5 (‘‘tiles’’) has been studied. We identify the important role played by correlations arising from the stacking of flat surfaces in stabilizing the layered order. We find that 5×1×1 rods can also exhibit such correlations through orientational disorder. Over this range of particle shapes no nematic phase is observed.
Publisher: American Physical Society (APS)
Date: 24-09-2010
Publisher: American Chemical Society (ACS)
Date: 06-05-2011
DOI: 10.1021/JP111835Z
Abstract: We use calorimetrically detected crystal nucleation and growth studies to broaden the discussion of fluctuation-induced nucleation processes to include composition fluctuations in ionic complex-forming systems. We use the model system Ca(NO(3))(2)-KNO(3) with NaNO(3) introduced as a third component, so that crystallization kinetics can be controlled by change of alkali cation at constant mole fraction of Ca(NO(3))(2). At fixed NaNO(3) content, we find separate and thermodynamically anomalous kinetics for the crystallization of NaNO(3) and Ca(NO(3))(2),which we attribute to the importance of slow concentration fluctuations in the latter case. The "nose" of the time-temperature-transformation TTT curve for crystallization of the Ca(NO(3))(2) occurs at much higher temperatures and longer times than that for NaNO(3) and the shape of the curve is different. Above the metastable liquidus surface of NaNO(3), supercooled ternary melts can persist for long times. Suppression of the fast NaNO(3) crystallization, by replacement of Na(+) by K(+), is a prerequisite for easy vitrification in this system.
Publisher: AIP Publishing
Date: 28-01-2018
DOI: 10.1063/1.5010051
Abstract: We study the influence of the liquid-vapor surface on the crystallization kinetics of supercooled metal alloys. While a good glass former, Cu50Zr50, shows no evidence of surface enhancement of crystallization, Ni50Al50 exhibits an increased rate of crystallization due to heterogeneous nucleation at the free liquid surface. The difference in the compositional fluctuations at the interface is proposed as the explanation of the distinction between the two alloys. Specifically, we observe compositional ordering at the surface of Ni50Al50, while the Cu50Zr50 alloy only exhibits a diffuse adsorption of the Cu at the interface. We argue that the general difference in composition susceptibilities at planar surfaces represents an important factor in understanding the difference in the glass forming ability of the two alloys.
Publisher: AIP Publishing
Date: 12-1985
DOI: 10.1063/1.449595
Publisher: American Chemical Society (ACS)
Date: 22-05-2004
DOI: 10.1021/JP037760R
Publisher: American Physical Society (APS)
Date: 04-2005
Publisher: Elsevier BV
Date: 09-2002
Publisher: American Chemical Society (ACS)
Date: 21-04-2011
DOI: 10.1021/JP1108619
Publisher: Institution of Engineering and Technology (IET)
Date: 22-02-2018
Publisher: AIP Publishing
Date: 08-07-2022
DOI: 10.1063/5.0094386
Abstract: The persistent problem posed by the glass transition is to develop a general atomic level description of amorphous solidification. The answer proposed in this paper is to measure a configuration’s capacity to restrain the motion of the constituent atoms. Here, we show that the instantaneous normal modes can be used to define a measure of atomic restraint that accounts for the difference between fragile and strong liquids and the collective length scale of the supercooled liquid. These results represent a significant simplification of the description of amorphous solidification and provide a powerful systematic treatment of the influence of microscopic factors on the formation of an amorphous solid.
Publisher: IOP Publishing
Date: 20-08-2010
DOI: 10.1088/0953-8984/22/36/364106
Abstract: The square gradient free energy functional is used to describe the distribution of sub-critical crystalline fluctuations in a supercooled liquid. We show that for any supercooling there exists a cluster radius of 3-4 particle diameters below which the crystalline order is no longer stable. We explore the consequences of this observation.
Publisher: American Physical Society (APS)
Date: 14-10-2009
Publisher: AIP Publishing
Date: 18-01-2008
DOI: 10.1063/1.2815325
Abstract: In this paper we establish the temperature dependence of the kinetic coefficient associated with crystal growth into the supercooled liquid for a wide range of organic and inorganic materials. We show that the kinetic coefficient for crystal growth scales with the shear viscosity η as η−ξ and that the exponent depends systematically on the fragility of the liquid. The greater the fragility (i.e., deviation away from an Arrhenius temperature dependence for η), the larger the difference 1−ξ. We argue that this breakdown in scaling between the crystal growth kinetics and the viscosity is a manifestation of heterogeneous dynamics in supercooled liquids. In addition, we show that the absolute growth rate at intermediate viscosities is correlated with the entropy difference between the liquid and the crystal.
Start Date: 01-2007
End Date: 01-2012
Amount: $1,720,305.00
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