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

We combine the shoving model ofT-dependent viscosity of supercooled liquids with the Zwanzig-Mountainformula for the high-frequency shear modulus using theg(r) of molecular dynamics simulations of metal alloysas 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 whichg(r) was calculated. The model provides direct access to the influence of atomic-scale physical quantities suchas the interatomic potentialφ(r) on the viscosity and fragile-strong behavior. In particular, it is established thata steeper interatomic repulsion leads to fragile liquids, or, conversely, that “soft atoms make strong liquids.”