Slow dynamics in a primitive tetrahedral network model

We report extensive Monte Carlo and event-driven molecular dynamics simulations of the fluid and liquid phase of a primitive model for silica recently introduced by Ford, Auerbach and Monson [J. Chem. Phys. 17, 8415 (2004)]. We evaluate the iso-diffusivity lines in the temperature-density plane to provide an indication of the shape of the glass transition line. Except for large densities, arrest is driven by the onset of the tetrahedral bonding pattern and the resulting dynamics is strong in the Angell's classification scheme. We compare structural and dynamic properties with corresponding results of two recently studied primitive models of network forming liquids -- a primitive model for water and a angular-constraint free model of four-coordinated particles -- to pin down the role of the geometric constraints associated to the bonding. Eventually we discuss the similarities between "glass" formation in network forming liquids and "gel" formation in colloidal dispersions of patchy particles.Comment: 9 pages, 10 figure

What does the potential energy landscape tell us about the dynamics of supercooled liquids and glasses?

For a model glass-former we demonstrate via computer simulations how macroscopic dynamic quantities can be inferred from a PEL analysis. The essential step is to consider whole superstructures of many PEL minima, called metabasins, rather than single minima. We show that two types of metabasins exist: some allowing for quasi-free motion on the PEL (liquid-like), the others acting as traps (solid-like). The activated, multi-step escapes from the latter metabasins are found to dictate the slowing down of dynamics upon cooling over a much broader temperature range than is currently assumed

Dynamics and energy landscape in a tetrahedral network glass-former: Direct comparison with models of fragile liquids

We report Molecular Dynamics simulations for a new model of tetrahedral network glass-former, based on short-range, spherical potentials. Despite the simplicity of the forcefield employed, our model reproduces some essential physical properties of silica, an archetypal network-forming material. Structural and dynamical properties, including dynamic heterogeneities and the nature of local rearrangements, are investigated in detail and a direct comparison with models of close-packed, fragile glass-formers is performed. The outcome of this comparison is rationalized in terms of the properties of the Potential Energy Surface, focusing on the unstable modes of the stationary points. Our results indicate that the weak degree of dynamic heterogeneity observed in network glass-formers may be attributed to an excess of localized unstable modes, associated to elementary dynamical events such as bond breaking and reformation. On the contrary, the more fragile Lennard-Jones mixtures are characterized by a larger fraction of extended unstable modes, which lead to a more cooperative and heterogeneous dynamics.Comment: 26 pages, 18 figures, added links to animations, corrected typos in sec.

Description of the dynamics in complex energy landscapes via metabasins: a simple model study

We study the dynamics in a simple hierarchical energy landscape. We compare a straightforward analytical approximation with the results of Monte Carlo simulations. The model is devised to mimic some aspects of the dynamics in supercooled liquids. We show that the concept of metabasins, as recently discussed in the framework of the potential energy landscape of glasses, emerges quite naturally

Description of the dynamics in complex energy landscapes via metabasins: a simple model study

We study the dynamics in a simple hierarchical energy landscape. We compare a straightforward analytical approximation with the results of Monte Carlo simulations. The model is devised to mimic some aspects of the dynamics in supercooled liquids. We show that the concept of metabasins, as recently discussed in the framework of the potential energy landscape of glasses, emerges quite naturally