Revisiting scaling laws for the diffusion coefficients in simple melts based on the structural deviation from hard-sphere-like case

Molecular simulations of a series of simple melts, including Al, Cu, Ni, Pt, Ti, Si and Ge, are used to study the scaling laws of diffusion coefficients proposed by Rosenfeld and Dzugutov. Our simulation results give strong support to the result that the scaling laws of diffusion coefficients hold true for simple liquids with isotropic many-body interactions but fail for systems with anisotropic interatomic interaction. The failure of the scaling laws in application liquid Si (l-Si) and liquid Ge (l-Ge) is connected to the fact that the excess entropy of them cannot be calculated approximately in terms of the two-body contribution and the original reduction parameters are no longer appropriate. In particular, since the ratio between the positions of the second and first peaks in structure factor (Q2/Q1) is a direct measure of the structural deviation from the hard-sphere-like case, the temperature dependence of Q2/Q1 was analyzed. Moreover, in comparison with 1.86, the value of Q2/Q1 for the hard-sphere-like case, we modified the scaling laws of diffusion coefficients proposed by Rosenfeld and Dzugutov. The modified scaling relations are appropriate not only for simple liquid metals, but also for l-Si and l-Ge with anisotropic interatomic interaction.