Aging to equilibrium dynamics of SiO2

作者：Vollmayr Lee K^*; Roman J A; Horbach J

来源：Physical Review E, 2010, 81(6): 061203.

DOI：10.1103/PhysRevE.81.061203

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 T-i is an element of {5000 K, 3760 K}, the system is quenched to lower temperatures T-f is an element of {2500 K, 2750 K, 3000 K, 3250 K} and observed after a waiting time t(w). 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 C-q(t(w), t(w) + t), and for the mean-square displacement Delta r(2)(t(w), t(w) + t). We conclude that there are three different t(w) regions: (I) At very short waiting times, C-q(t(w), t(w) + t) decays very fast without forming a plateau. Similarly Delta r(2)(t(w), t(w) + t) increases without forming a plateau. (II) With increasing tw a plateau develops in C-q(t(w), t(w) + t) and Delta r(2)(t(w), t(w) + t). For intermediate waiting times the plateau height is independent of t(w) and T-i. Time superposition applies, i.e., C-q=C-q(t/t(r)(Cq)) where t(r)(Cq)=t(r)(Cq)(t(w)) is a waiting time-dependent decay time. Furthermore C-q=C(q, t(w), t(w) + t) scales as C-q=C(q, z(t(w), t) where z is a function of t(w) and t only, i.e., independent of q. (III) At large t(w) the system reaches equilibrium, i.e., C-q(t(w), t(w) + t) and Delta r(2)(t(w), t(w) + t) are independent of t(w) and T-i. For C-q(t(w), t(w) + t) we find that the time superposition of intermediate waiting times (II) includes the equilibrium curve (III).

• 出版日期2010-6-25