Abstract
The mode-coupling formalism for the memory function of the velocity autocorrelation function formulated roughly 10 years ago by Sjölander, Sjögren and Wahnström is believed to describe the dynamical properties of argon and rubidium in the liquid state relatively well. Moreover, mode-coupling theory has been successfully applied to interpret a number of dynamical phenomena observed in a supercooled liquid approaching the liquid-glass transition. The results of a mode-coupling theory limited to four coupling terms and extended to Q-dependent memory functions over the region of 0–6 Å −1 are discussed. The comparison with molecular dynamics (MD) data demonstrates that mode-coupling theory overestimates the long-time tail of the second-order memory function and fails to describe correctly the self-motion of liquid lead both at low and high temperature. The self-diffusion coefficient obtained from a mode-coupling calculation is about 25% too low. However, the analysis of the results at two different temperatures indicates that there is a systematic pattern in the discrepancies which suggests a possibility to improve the theoretical approach to match the MD-results.
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