Microscopic motions and the local environments of atoms in simple liquids

Abstract

Molecular dynamics simulations are carried out in order to understand the microscopic mechanism of atomic motions in simple liquids. The radial distribution function is classified into subgroups by taking a partial average over the atoms having the same coordination number in the first shell. By considering this classified distribution of atoms as an initial one, the time evolution of the radial distribution function, and the velocity auto- and cross-correlation functions are calculated in each subgroup. Investigation through these ‘‘microscopic’’ correlation functions reveals the details of atomic motions which would be obscured if the totally averaged correlation functions were used. It is found that an atom in a region of low local density oscillates weakly for a long period, because the low-density region is surrounded, on the average, by the high density region of atoms. On the other hand, an atom in a region of high local density receives a strong rebound from the neighboring atoms, but behaves less oscillatory at subsequent times, because the neighboring atoms move toward the outer region of low density.