Simulations of glasses: multiscale modeling and density of states Monte-Carlo simulations

We show the application of two recent developments in molecular simulations, density of states (DOS) (Wang-Landau) Monte-Carlo and multiscale modeling, to the understanding of the glass transition. First, we review DOS Monte-Carlo using the two-dimensional Ising model without external field on lattices of varying size. We point out that we can analyze the resulting densities of state in a canonical and a microcanonical way starting from the same simulations. The heat capacity is discussed in both ensembles. Results from both ensembles of off-lattice simulations of a model binary glass former are compared as well. Subsequently, a self-consistent systematic mapping procedure for molecular models from the atomistic to the mesoscale is presented. It allows to efficiently derive mesoscale models with fewer interaction centers from atomistic models preserving the molecular identity. We use the optimization of a corresponding mesoscale model for atactic polystyrene (a good glass former) in the melt as an example. Simulations of different temperatures using this model allow some insight into the glass formation of this system. We point out the strengths and weaknesses of these approaches and give an outlook towards their combination.