Stress autocorrelation function in liquid rubidium

A molecular-dynamics simulation of the stress autocorrelation function {η}(t) is reported for a dense-liquid-rubidium model. The data indicate a rapid decay of the correlation function for t{}0.3 ps and a somewhat slower time dependence thereafter. Mode-coupling theory, and an alternative dynamical approach involving a conditional probability distribution function, are discussed and then applied in an attempt to explain these data. The former is shown to give a very good account of our results at intermediate and long times, and a simple means of extrapolating the theory to small times is suggested. In our case excellent overall agreement with the computer data is achieved. The dependence of {η}(t) on the intermediate-scattering function F(q,t), as predicted by the mode-coupling result, confirms the importance of collective atomic rearrangements in the dynamics of shear-stress relaxation.