A molecular-dynamics study of the dynamic properties of liquid rubidium. II. Single-particle correlation functions

Abstract

For pt. I see ibid., vol. 6, p. 10897 (1994). We present results for the dynamic single-particle correlation functions (i.e., the intermediate self-scattering function and the velocity autocorrelation function) of six liquid states of rubidium obtained in the same computer experiment as described in the preceding paper. Since the incoherent structure factor for Rb cannot be determined in a neutron-scattering experiment. Our computer results could not be compared to experimental data. Temperature effects have been studied for both correlation functions: (i) an increasing temperature causes the single-particle correlations to decay much more rapidly than at low temperatures; (ii) the velocity autocorrelation function becomes a much more slowly decaying function in time. This reflects the cage (drift) effect encountered in dense (expanded) systems. An attempt to interpret the peak height and half-width of the self-dynamic structure factor in terms of mode-coupling theories has failed: either these subtle effects are encountered in a q-range inaccessible to computer experiment, or they require a more sophisticated analysis in terms of a full mode-coupling-theory approach. The diffusion constant extracted from the single-particle correlation functions shows good agreement with data obtained from the collective correlation functions, which marks a good internal consistency of the computer experiment.