Crossover from fragile liquids to strong liquids near the glass transition created by isotropic two-body short-range interactions

The extensive molecular-dynamics simulations on binary mixtures A80B20 with a Stillinger–Weber potential are performed to obtain two types of glass-forming liquids near the glass transition, fragile and strong liquids. The simulations are done for different mass ratios Q ( = m B / m A ) under the same potential with m A being fixed, where m α denotes a mass of α particle. The simulation results for the self-diffusion coefficient D are then analyzed by two types of master curves recently proposed as D = d 0 x − 1 ( 1 − x ) 2 + η exp [ 62 x 3 + η ( 1 − x ) 2 + η ] with η = 4 / 3 for fragile liquids and 5/3 for strong liquids, where x is a reduced inverse temperature and d 0 a positive constant. Then, it is shown that for Q < Q c the simulation results for the diffusion coefficient obey the fragile master curve with η = 4 / 3 , while for Q > Q c they obey the strong master curve with η = 5 / 3 , where Q c ≃ 20 . The structural relaxation time τ α and the β -relaxation time τ β are also shown to obey the power laws recently proposed as τ α ∼ D − ( 1 + μ ) and τ β ∼ D − ( 1 − μ ) in a supercooled region, respectively, while τ α ∼ τ β ∼ D − 2 / 3 in a liquid region, where μ = 2 / ( 3 ( η + 2 ) ) . Here μ ≃ 1 / 5 for fragile liquids and 2/11 for strong liquids. These situations are exactly the same as those in usual glass-forming liquids. Thus, it is emphasized that two types of glass-forming liquids can be simply created by simple short-range potentials.