Cooperative motions in a finite size model of liquid silica: an anomalous behavior |
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Authors: | V Teboul |
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Institution: | (1) Laboratoire des Propriétés Optiques des Matériaux et Applications, CNRS UMR 6136, Université d'Angers, 2 Bd Lavoisier, 49045 Angers Cedex, France |
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Abstract: | Finite size effects on dynamical heterogeneity are studied in liquid silica
with Molecular Dynamics simulations using the BKS potential model. When the
system size decreases relaxation times are found to increase in accordance
with previous results in finite-size simulations and confined liquids. It
has been suggested that this increase may be related to a modification of
the spatially heterogeneous dynamics in confined liquids. In agreement with
this hypothesis we observe a decrease of the spatially heterogeneous
dynamics when the size decreases. The spatially heterogeneous dynamics is
usually characterized by the dynamical aggregation of the most or the least
mobile atoms. However we find that the decrease of the dynamical aggregation
associated to the least mobile atoms is much more important than the
decrease associated to the most mobile atoms when the size decreases. This
result associated with a slowing down of the liquid is surprising as it is
expected that the dynamical aggregation of the least mobile atoms should
increase the slowing down of the liquid dynamics. The decrease of the
heterogeneous behaviour is also in contradiction with the increase of the
spatially heterogeneous dynamics observed in liquids confined inside
nanopores. However, an increase of the non-Gaussian parameter appears both
for the confinement inside nanopores and for the finite size simulations. As
the non-Gaussian parameter is usually associated with the heterogeneous
dynamics, the increase of the non-Gaussian parameter together with a
decrease of the spatially heterogeneous dynamics is also surprising. |
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Keywords: | 61 43 Fs Glasses 64 70 Pf Glass transitions 66 10 Cb Diffusion and thermal diffusion |
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