Study of spatial correlation functions near the glass transition by molecular dynamics simulations

We study spatial–temporal correlation functions of the direction and the mobility fluctuation by performing molecular dynamics simulations, in which the pair-interaction is described by the Lennard-Jones potential. We focus attention on coexistence states between liquid and crystal for single-component systems. Although the correlation of the direction in coexistence states is little different from that in liquids, the correlation of the mobility fluctuation in coexistence states is extremely high compared to that in liquids. In addition, we predict length scales expected from the correlation functions. The correlation lengths of both the direction and the mobility fluctuation suddenly increase at the freezing point. Especially, the length of the mobility fluctuation in coexistence states seems to diverge. We also compare the results in single-component systems to those of supercooled liquids in Lennard-Jones binary mixtures according to the suggestion that there are crystal-like ordered regions in supercooled liquids near the glass transition. Recalling the fact that the correlation lengths do not diverge even near the glass transition, its dynamics of the supercooled liquids near the glass transition and that of the coexistence states are quite different, while the static structure resembles each other.