Dynamics of atomic pairs in a Lennard-Jones fluid: Mean relative displacement analysis

Abstract

We have analyzed the dynamics of atomic pairs in a simple fluid in terms of the mean relative displacement of two atoms with a given initial separation. The short-time expansion of the mean relative displacement has been derived exactly beyond the constant acceleration approximation (CAA) (up to the t(4) order). For a Lennard-Jones fluid, the mean relative displacements calculated by either the CAA or the t(4)-order approximation have been compared with the results obtained from a molecular-dynamics simulation. Through studying the relative motions of atomic pairs with different initial separations, we give a physical picture of the dynamics of neighboring atoms beyond the CAA. [S1063-651X(99)08603-1].