Potential energy landscape and mechanisms of diffusion in liquids

The mechanism of diffusion in supercooled liquids is investigated from the potential energy landscape point of view, with emphasis on the crossover from high- to low-T dynamics over the range T(A) > or =T > or =T(c). Molecular dynamics simulations with a time dependent mapping to the associated local minimum or inherent structure (IS) are performed on unit-density Lennard-Jones. Dynamical quantities introduced include r2(is)(t), the mean-square displacement (MSD) within a basin of attraction of an IS, R2(t), the MSD of the IS itself, and g(t), the distribution of IS waiting times. The configuration space is treated as a composite of the contributions of cooperative local regions, and a method is given to obtain the physically meaningful g(loc)(t) and mean waiting time tau(loc) from g(t). An understanding of the crossover is obtained in terms of r2(is)(t) and tau(loc). At intermediate T, r2(is)(t) possesses an interval of linear t dependence allowing calculation of an intrabasin diffusion constant D(is). Near T(c), where intrabasin diffusion is well established for t