Crossover (or Kovacs) effect in an aging molecular liquid.

We study by means of molecular dynamics simulations the aging behavior of a molecular model of ortho-terphenyl. We find evidence of a nonmonotonic evolution of the volume during an isothermal-isobaric equilibration process, a phenomenon known in polymeric systems as the crossover (or Kovacs) effect. We characterize this phenomenology in terms of landscape properties, providing evidence that, far from equilibrium, the system explores regions of the potential energy landscape distinct from the one explored in thermal equilibrium.