Forty Years of Silica Simulations: Which Way Now?

Ten years after Aneesur Rahman's seminal 1964 paper on simulating liquid argon using computer simulations of atoms interacting with continuous potentials, Woodcock and Singer published the first study of ionic liquids using the same classical mechanical approach. With tongue-in-cheek, Woodcock and Angell with student Cheeseman then studied SiO₂ in a simple ionic model using Tosi-Fumi type potentials and were surprised by the degree of similarity to the unusual properties of the "real" silica, liquid, and glassy, they were able to obtain. Since that time, many advances have been made and the field of ionic liquids now embraces geochemical in addition to complex inorganic glass systems. Now it seems that some "silica" models may exhibit water-like second critical points, and then liquid-liquid transitions, and so may serve as new model liquids for liquid polyamorphism studies. Current studies using the realistic van Beest-Kramer-van Santen(BKS) and the simpler Woodcock-Angell-Cheeseman(WAC) potential models will be described. We provide background on silica's role as a "strong" liquid, and on the criterion for ergodicity breaking which requires the relation Qdτ/dT ≈ 1 to hold at the hysteresis peak T_p (coincides with three common definitions of T_g).