Simulation study of polymorphism and diffusion anomaly for SiO2 and GeO2 liquid

We report molecular dynamic (MD) simulations of a silica and germania liquid. We show for the first time that the liquid models constructed of the BKS and Ocffner-Elliott potential are composed of D-4, D-5 and D-6 domains. These domains of different liquids (identical chemical composition but different density) are structurally identical. The liquid densification occurs gradually with variation in the volume of the D-4, D-5 and D-6 domains. The void radius distributions (VRD) have been computed and they are well fitted to a Gaussian form. Both the average void radii and width of the VRD decrease with pressure. The diffusivity of Si/Ge or O depends linearly on the fraction of TOx (x = 4, 5 and 6; T is Ge or Si). The diffusion anomaly results from the very high mobility of silicon in the D-5 domain compared to domains D-4 and D-6.