title: Aging to equilibrium dynamics of SiO2.
abstract: Molecular dynamics computer simulations are used to study the aging dynamics of SiO2 (modeled by the BKS model). Starting from fully equilibrated configurations at high temperatures Ti∊{5000 K,3760 K}, the system is quenched to lower temperatures Tf∊{2500 K,2750 K,3000 K,3250 K} and observed after a waiting time tw. Since the simulation runs are long enough to reach equilibrium at Tf, we are able to study the transition from out-of-equilibrium to equilibrium dynamics. We present results for the partial structure factors, for the generalized incoherent intermediate scattering function Cq(tw,tw+t), and for the mean-square displacement Δr2(tw,tw+t). We conclude that there are three different tw regions: (I) At very short waiting times, Cq(tw,tw+t) decays very fast without forming a plateau. Similarly Δr2(tw,tw+t) increases without forming a plateau. (II) With increasing tw a plateau develops in Cq(tw,tw+t) and Δr2(tw,tw+t). For intermediate waiting times the plateau height is independent of tw and Ti. Time superposition applies, i.e., Cq=Cq(t/trCq) where trCq=trCq(tw) is a waiting time-dependent decay time. Furthermore Cq=C(q,tw,tw+t) scales as Cq=C(q,z(tw,t)) where z is a function of tw and t only, i.e., independent of q. (III) At large tw the system reaches equilibrium, i.e., Cq(tw,tw+t) and Δr2(tw,tw+t) are independent of tw and Ti. For Cq(tw,tw+t) we find that the time superposition of intermediate waiting times (II) includes the equilibrium curve (III).
authors.affiliation: Department of Physics and Astronomy, Bucknell University, Lewisburg, Pennsylvania 17837, USA. kvollmay@bucknell.edu
authors.forename: K
authors.initials: K
authors.lastname: Vollmayr-Lee
authors.forename: J A
authors.initials: JA
authors.lastname: Roman
authors.forename: J
authors.initials: J
authors.lastname: Horbach