Atomic-scale expressions for viscosity and fragile-strong behavior in metal alloys based on the Zwanzig-Mountain formula

Abstract

We combine the shoving model of T-dependent viscosity of supercooled liquids with the Zwanzig-Mountain formula for the high-frequency shear modulus using the g(r) of molecular dynamics simulations of metal alloys as the input. This scheme leads to a semianalytical expression for the viscosity as a function of temperature, which provides a three-parameter model fitting of experimental data of viscosity for the same alloy for which g(r) was calculated. The model provides direct access to the influence of atomic-scale physical quantities such as the interatomic potential φ(r) on the viscosity and fragile-strong behavior. In particular, it is established that a steeper interatomic repulsion leads to fragile liquids, or, conversely, that "soft atoms make strong liquids."