title: Search for a liquid-liquid critical point in models of silica.
abstract: Previous research has indicated the possible existence of a liquid-liquid critical point (LLCP) in models of silica at high pressure. To clarify this interesting question we run extended molecular dynamics simulations of two different silica models (WAC and BKS) and perform a detailed analysis of the liquid at temperatures much lower than those previously simulated. We find no LLCP in either model within the accessible temperature range, although it is closely approached in the case of the WAC potential near 4000 K and 5 GPa. Comparing our results with those obtained for other tetrahedral liquids, and relating the average Si-O-Si bond angle and liquid density at the model glass temperature to those of the ice-like β-cristobalite structure, we conclude that the absence of a critical point can be attributed to insufficient "stiffness" in the bond angle. We hypothesize that a modification of the potential to mildly favor larger average bond angles will generate a LLCP in a temperature range that is accessible to simulation. The tendency to crystallize in these models is extremely weak in the pressure range studied, although this tendency will undoubtedly increase with increasing stiffness.
authors.affiliation: Center for Polymer Studies and Department of Physics, Boston University, Boston, Massachusetts 02215, USA.
authors.forename: Erik
authors.initials: E
authors.lastname: Lascaris
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287, USA.
authors.forename: Mahin
authors.initials: M
authors.lastname: Hemmati
authors.affiliation: Department of Physics, Yeshiva University, 500 West 185th Street, New York, New York 10033, USA.
authors.forename: Sergey V
authors.initials: SV
authors.lastname: Buldyrev
authors.affiliation: Center for Polymer Studies and Department of Physics, Boston University, Boston, Massachusetts 02215, USA.
authors.forename: H Eugene
authors.initials: HE
authors.lastname: Stanley
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287, USA.
authors.forename: C Austen
authors.initials: CA
authors.lastname: Angell