The distance between Inherent Structures and the influence of saddles on approaching the mode coupling transition in a simple glass former

We analyze through molecular dynamics simulations of a Lennard-Jones binary mixture the statistics of the distances between inherent structures (IS) sampled at temperatures above the mode coupling transition temperature T_MCT. We take equilibrated configurations and randomly perturb the coordinates of a given number of particles. After that we take the nearest IS of both the original configuration and the perturbed one and evaluate the distance between them. This distance presents an inflection point near T~1 with a strong decrease below this temperature and goes to a small but nonzero value on approaching T_MCT. In the low temperature region we study the statistics of events which give zero distance, i.e. dominated by minima, and find evidence that the number of saddles decreases exponentially near T_MCT. This implies that saddles continue to exist even for T<=T_MCT. As at T_MCT the extrapolated diffusivity goes to zero our results imply that there are saddles associated with nondiffusional events at T<T_MCT.