There exists a variety of theories of the glass transition and many more numerical models. But because the models need built-in complexity to prevent crystallization, comparisons with theory can be difficult. We study the dynamics of a deeply supersaturated \emph{monodisperse} four-dimensional (4D) hard-sphere fluid, which has no such complexity, but whose strong intrinsic geometrical frustration inhibits crystallization, even when deeply supersaturated. As an application, we compare its behavior to the mode-coupling theory (MCT) of glass formation. We find MCT to describe this system better than any other structural glass formers in lower dimensions. The reduction in dynamical heterogeneity in 4D suggested by a milder violation of the Stokes-Einstein relation could explain the agreement. These results are consistent with a mean-field scenario of the glass transition.
At low enough temperatures and high densities, the equilibrium configuration of an ensemble of ultrasoft particles is a self-assembled, ordered, cluster-crystal. In the present work we explore the out-of-equilibrium dynamics for a two-dimensional realization, which is relevant to superconducting materials with multi-scale intervortex forces. We find that for small temperatures following a quench, the suppression of the thermally-activated particle hopping hinders the ordering. This results in a glass transition for a monodispersed ensemble, for which we derive a microscopic explanation in term…
The Adam-Gibbs (AG) relation connects the dynamics of a glass-forming liquid to its the thermodynamics via. the configurational entropy, and is of fundamental importance in descriptions of glassy behaviour. The breakdown of the Stokes-Einstein (SEB) relation between the diffusion coefficient and the viscosity (or structural relaxation times) in glass formers raises the question as to which dynamical quantity the AG relation describes. By performing molecular dynamics simulations, we show that the AG relation is valid over the widest temperature range for the diffusion coefficient and not for t…
Supercooled liquids are kinetically trapped materials in which the transition to a thermodynamically more stable state with long-range order is strongly suppressed. To assess the glass-forming abilities of a liquid empirical rules exist, but a comprehensive microscopic picture of devitrification is still missing. Here we study the crystallization of a popular model glass former, the binary Kob-Andersen mixture, in small systems. We perform trajectory sampling employing the population of the locally favored structure as order parameter. While for large population a dynamical phase transition ha…
Heat capacity of B2O3 glass former in a wide temperature region is described well with the intrinsic motions for non-spherical B2O3 molecules, revealing that rather than a conventional network glass former, B2O3 is a typical molecular matter in which the transition from liquid to glass in the system corresponds to the frozen of translational motions for molecules. The finding might provide an opportunity to understand the mysterious glass transition, as well as the intrinsic difference between solids and liquids.
A theory is developed to calculate values of the potential energy barriers to structural relaxation in molecular glass formers from the data of static pair correlation function. The barrier height is shown to increase due to increase in number of the stable bonds a particle forms with its neighbours and energy of each bond as liquids move deeper into the supercooled (super-compressed) region. We present results for a system of hard-spheres and compare calculated values of the structural relaxation time with experimental and simulation results.
In this article we review results of computer simulation of glasses carried out using first principles approaches, notably density functional theory. We start with a brief introduction to this method and compare the pros and cons of this approach with the ones of simulations with classical potentials. This is followed by a discussion of simulation results of various glass-forming systems that have been obtained via ab initio simulations and that demonstrate the usefulness of this approach to understand the properties of glasses on the microscopic level.
The statistical properties of infrequent particle displacements, greater than a certain distance, is known as jump dynamics in the context of structural glass formers. We generalize the concept of jump to the case of a spin glass, by dividing the system in small boxes, and considering infrequent cooperative spin flips in each box. Jumps defined this way share similarities with jumps in structural glasses. We perform numerical simulations for the 3D Edwards-Anderson model, and study how the properties of these jumps depend on the waiting time after a quench. Similar to the results for structura…
Whether the glass transition is caused by an underlying singularity or is a purely kinetic phenomenon is a significant outstanding question. Studying an atomistic glass former, we introduce a sampling method to access temperatures corresponding to dynamical regimes usually hard to reach with computer simulation. We find a peak in the specific heat, which we interpret as a drop in the density of states. We further present evidence of a liquid-liquid transition to a state rich in locally favoured structures related to a recently discovered dynamical phase transition.
We study the nature of the glass transition by cooling model atomistic glass formers at constant rate from a temperature above the onset of glassy dynamics to $T=0$. Motivated by the East model, a kinetically constrained lattice model with hierarchical relaxation, we make several predictions about the behavior of the supercooled liquid as it passes through the glass transition. We then compare those predictions to the results of our atomistic simulations. Consistent with our predictions, our results show that the relaxation time $τ$ of the material undergoes a crossover from super-Arrhenius to…
Using molecular dynamics simulations we investigate the finite-size dependence of the dynamical properties of a diatomic supercooled liquid. The simplicity of the molecule permits us to access the microsecond time scale. We find that the relaxation time decreases simultaneously with the strength of cooperative motions when the size of the system decreases. While the decrease of the cooperative motions is in agreement with previous studies, the decrease of the relaxation time opposes what has been reported to date in monatomic glass formers and in silica. This result suggests the presence of di…
We numerically study the equilibrium relaxation dynamics of a two-dimensional Mari-Kurchan glass model. The tree-like structure of particle interactions forbids both non-trivial structural motifs and the emergence of a complex free-energy landscape leading to a thermodynamic glass transition, while the finite-dimensional nature of the model prevents the existence of a mode-coupling singularity. Nevertheless, the equilibrium relaxation dynamics is shown to be in excellent agreement with simulations performed in conventional glass-formers. Averaged time-correlation functions display a phenomenol…
In a dense colloidal suspension at a volume fraction slightly lower than that of its glass transition, we follow the trajectories of an assembly of tracers over a large time window. We define a local activity, which quantifies the local tendency of the system to rearrange. We determine the statistics of the time and space integrated activity, and we argue that it develops a low activity tail that comes on a par with the onset of glassy behavior and heterogeneous dynamics. These rare events may be interpreted as the reflection of an underlying dynamic phase transition.
We investigate the static and dynamic properties of a weakly polydisperse hard sphere system in the deeply supercooled state, i.e. at densities higher than that corresponding to the mode-coupling transition. The structural analysis reveals the emergence of icosahedral locally favoured structures, previously only found in trace quantities. We present a new approach to probe the shape of dynamically heterogeneous regions, which is insensitive to particle packing effects that can hamper such analysis. Our results indicate that the shape of the dynamically heterogeneous regions changes only weakly…
