Quench, Equilibration, and Subaging in Structural Glasses
In the glassy state, all materials undergo a process of structural recovery as they age towards equilibrium. The resultant increase of relaxation times tα is frequently described with a sublinear power of the wait time twμ with an apparent aging exponent μ. We show with molecular dynamics simulations of a Lennard-Jones glass former at various temperatures that the observed aging exponent can be strongly influenced by crossover effects from the freshly quenched state at short tw and into the equilibrated state at long tw. The aging behavior on the molecular level is quantitatively reproduced by a coarse-grained continuous time random walk description over the entire range of temperatures and wait times. Our model glass always shows normal aging, tα∼tw, when the observation time window is no longer affected by crossover effects, in agreement with the well-known trap model of aging.