Fast and Slow Dynamics in Metasilicate Galsses

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Molecular dynamics (MD) simulations of lithium metasilicate (Li_2SiO_3) glass has been performed. Dynamics of lithium ions in metasilicate glass were found to divide into fast and slow ones in the glassy state. We have divided the particles into type A (slow dynamics) and B (fast dynamics). We have examined the characteristics of the dynamics and structure with distinguishing between type A and B particles. Type A particles are located within neighboring sites during a 1 ns run. Such particles show only single jumps and tend to return to their previous sites due to low dimensional local paths. The particles with long waiting time of the jump motion is also included type A particles. On the other hand, type B particles show accelerated dynamics. Cooperative jumps (simultaneous jumps of neighboring ions or occuring within several ps before the relaxation of the jump sites) cause the acceleration. Power law distributions of the displacements reveal that the fast dynamics is characterized as Levy flight. Short intervals of the jump events also take place in the fast dynamics at short time region. We have found the difference in the medium range structure concerning type A and B particles. The structure for type B particles seems to be favorable to cause the cooperative jumps.
2000-04-28