arXiv subjects

Andrea Ninarello

Publications and source records attributed to Andrea Ninarello.

22 records · Page 2Linked to original sources

arXiv2017

Configurational entropy measurements in extremely supercooled liquids that break the glass ceiling

Liquids relax extremely slowly upon approaching the glass state. One explanation is that an entropy crisis, due to the rarefaction of available states, makes it increasingly arduous to reach equilibrium in that regime. Validating this scenario is challenging, because experiments offer limited resolution, while numerical studies lag more than eight orders of magnitude behind experimentally-relevant timescales. In this work we not only close the colossal gap between experiments and simulations but manage to create in-silico configurations that have no experimental analog yet. Deploying a range of computational tools, we obtain four estimates of their configurational entropy. These measurements consistently confirm that the steep entropy decrease observed in experiments is also found in simulations, even beyond the experimental glass transition. Our numerical results thus extend the new observational window into the physics of glasses and reinforce the relevance of an entropy crisis for understanding their formation.

cond-mat.stat-mech↗

arXiv2017

Models and algorithms for the next generation of glass transition studies

Successful computer studies of glass-forming materials need to overcome both the natural tendency to structural ordering and the dramatic increase of relaxation times at low temperatures. We present a comprehensive analysis of eleven glass-forming models to demonstrate that both challenges can be efficiently tackled using carefully designed models of size polydisperse supercooled liquids together with an efficient Monte Carlo algorithm where translational particle displacements are complemented by swaps of particle pairs. We study a broad range of size polydispersities, using both discrete and continuous mixtures, and we systematically investigate the role of particle softness, attractivity and non-additivity of the interactions. Each system is characterized by its robustness against structural ordering and by the efficiency of the swap Monte Carlo algorithm. We show that the combined optimisation of the potential's softness, polydispersity and non-additivity leads to novel computer models with excellent glass-forming ability. For such models, we achieve over ten orders of magnitude gain in the equilibration timescale using the swap Monte Carlo algorithm, thus paving the way to computational studies of static and thermodynamic properties under experimental conditions. In addition, we provide microscopic insights into the performance of the swap algorithm which should help optimizing models and algorithms even further.

cond-mat.stat-mech↗

arXiv2016

Equilibrium sampling of hard spheres up to the jamming density and beyond

We implement and optimize a particle-swap Monte-Carlo algorithm that allows us to thermalize a polydisperse system of hard spheres up to unprecedentedly-large volume fractions, where \revise{previous} algorithms and experiments fail to equilibrate. We show that no glass singularity intervenes before the jamming density, which we independently determine through two distinct non-equilibrium protocols. We demonstrate that equilibrium fluid and non-equilibrium jammed states can have the same density, showing that the jamming transition cannot be the end-point of the fluid branch.

cond-mat.stat-mech↗

arXiv2015

Structure and dynamics of coupled viscous liquids

We perform Monte-Carlo simulations to analyse the structure and microscopic dynamics of a viscous Lennard-Jones liquid coupled to a quenched reference configuration of the same liquid. The coupling between the two replicas is introduced via a field epsilon conjugate to the overlap Q between the two particle configurations. This allows us to study the evolution of various static and dynamic correlation functions across the (epsilon, T) equilibrium phase diagram. As the temperature is decreased, we identify increasingly marked precursors of a first-order phase transition between a low-Q and a high-Q phase induced by the field epsilon. We show in particular that both static and dynamic susceptibilities have a maximum at a temperature-dependent value of the coupling field, which defines a `Widom line'. We also show that, in the high-overlap regime, diffusion and structural relaxation are strongly decoupled because single particle motion mostly occurs via discrete hopping on the sites defined by the reference configuration. These results, obtained using conventional numerical tools, provide encouraging signs that an equilibrium phase transition exists in coupled viscous liquids, but also demonstrate that important numerical challenges must be overcome to obtain more conclusive numerical evidence.

cond-mat.stat-mech↗