CONFIGURATIONAL RELAXATION IN DENSE LIQUIDS BASED ON SEQUENTIALLY CORRELATED DISPLACEMENTS - ORIGIN AND LIMITATIONS OF NONEXPONENTIAL DECAY

A model for configurational relaxation in a hard sphere liquid is described in which it is assumed that individual atomic displacements are sequentially dependent upon the displacement of other atoms, these sequences originating with atoms adjacent to a small number of vacancies (packing defects) scattered randomly throughout the sample. This results in an inhomogeneous distribution of waiting times for displacement of atoms located at different distances from the vacancies. The inhomogeneity is formalized as a normalized distribution in s, the state of interference. Solution of the master equations yields a description of the redistribution of atoms among states at equilibrium. Configurational relaxation is represented by the autocorrelation for atoms neighboring vacancies. Relaxation exhibits a time regime characterized by nonexponential decay, followed by transition to a simple exponential decay at longer times. Persistence of the nonexponential regime increases with decreasing vacancy concentration. The change in decay law can be identified with a crossover from localized to global redistribution of the vacancies. Comparisons with empirical relaxation functions and implications for macroscopic properties are noted. © 1990 American Institute of Physics.