COMPARISON OF THE RESULTS OF MODE-COUPLING THEORY FOR LIQUID LEAD AT 623-K AND 1170-K WITH MOLECULAR-DYNAMICS DATA

The mode-coupling formalism for the memory function of the velocity au tocorrelation function formulated roughly 10 years ago by Sjolander, S jogren and Wahnstrom is believed to describe the dynamical properties of argon and rubidium in the liquid state relatively well. Moreover, m ode-coupling theory has been successfully applied to interpret a numbe r of dynamical phenomena observed in a supercooled liquid approaching the liquid-glass transition. The results of a mode-coupling theory lim ited to four coupling terms and extended to Q-dependent memory functio ns over the region of 0-6 angstrom-1 are discussed. The comparison wit h molecular dynamics (MD) data demonstrates that mode-coupling theory overestimates the long-time tail of the second-order memory function a nd 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 analys is of the results at two different temperatures indicates that there i s a systematic pattern in the discrepancies which suggests a possibili ty to improve the theoretical approach to match the MD-results.