Dynamical Correlation Functions and Memory Functions of Liquid Sodium. II. A Mode-Coupling Analysis

An analysis of the second-order memory functions, N ( k , t ) and N s ( k , t ), by the mode-coupling theory is presented for the density correlation function F ( k , t ) and its self-part F s ( k , t ), respectively, of liquid sodium near the triple point. The results obtained by the theory are compared with those of our recent molecular dynamics simulation. It is shown that the mode-coupling theory can explain quantitatively the behavior of the self-part N s ( k , t ) in the wide range of wavenumber k , though there appear small discrepancies between the theoretical and the MD results only within a small interval 0.1∼0.2 ps with increasing k . On the other hand, as for N ( k , t ), though the results obtained theoretically for small k are in good agreement with those obtained by the MD simulation, we have observed significant discrepancies between the theoretical and the MD results for relatively large k . That is, the theoretical curves have unexpected humps which are not observed in the MD simulation.