β relaxation in a highly supercooled state via molecular dynamics simulation

We have studied the β relaxation of the density autocorrelation for a two dimensional model fluid via molecular dynamics (MD) simulation. We have found that correlated motions composed of many particles occur in the time scales of about 20 times the time scales of the thermal oscillations, which corresponds to the β peak frequency of the imaginary self-part of the generalized susceptibility. It is also discussed that the self-part of the density autocorrelation function ${\mathit{F}}_{\mathit{s}}$(k,t) below the glass transition temperature (${\mathrm{\Gamma }}_{\mathrm{eff}}$=1.2–1.3) presents an oscillatory behavior at the time scales of about 100 times the time scales of the thermal oscillations, which may be caused by the periodic boundary conditions adopted in the MD simulation as usual.