Molecular dynamics study of a supercooled binary soft-sphere system: Calculation of the generalized susceptibility in supercooled and glassy states

To study how the motion of atoms changes through a glass forming process, we have carried out the molecular dynamics simulation for a binary soft-sphere system and calculated the self-part of the generalized susceptibility χ_s(q,ω) at various temperatures above/below T_g. At higher temperature, only one peak appears in the imaginary part of χs, which corresponds to random motion of atoms in the liquid state. When the temperature is reduced, the α-peak tends to separate out from the main peak and to move to lower frequencies. At the lowest temperature, the peak disappears from our frequency window. We show that the temperature dependence of the peak frequency is well described by the Vogel-Fulcher low. We also test the mode coupling theory. The two exponents do not agree with the universality of the mode coupling theory, λ = Γ(1 - a)²/Γ(1 + 2b) =const.