| Research Abstract |
Using 2-dimensional and 3-dimensional soft-sphere models, we have carried out molecular dynamics simulations for their supercooled fluid states. It has been shown that there are at least two different types of jumping motions of atoms in highly supercooled states and possibly glassy states, one of which, corresponding to the smaller averaged jump rate, can be specified by a distribution of the jump rates rather than a constant jump rate. These two jump motions are responsible to the alpha and beta slow dynamics in supercooled fluid states. Taking into consideration these two coarse-grained motions of atoms and trapping diffusion-type of equation (master equation) , we have found the following main results :
(1) Quasi anomalous diffusion takes place in highly supercooled fluid states, leading to the anomalous dynamics in intermediate time scales known as alpha and beta relaxation of the density autocorrelation function. (2) Below the glass transition temperature anomalous diffusion takes place, namely the diffusion constant becomes zero. This indicates that the anomaloous dynamics occurs in infinitely long time limit. The liquid-glass transition is specified in this theory by the Gaussian-to-non-Gaussian transition. (3) The above results are consistent with the behavior of the generalized susceptibility obtained by the molecular dynamics simulation, and with recent experiments.
In addition, as a related problem, we have also studied a system of charged polmer melts (plus counter ions) using molecular-dynamics simulation.
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