Dynamics of liquid and strongly supercooled alkali metals by instantaneous normal-mode analysis

The spectrum of instantaneous normal modes has been evaluated by molecular dynamics simulation for cesium in liquid and glassy states. The velocity autocorrelation function derived from the real-frequency part of the spectrum compares favorably with that calculated directly from simulation data, especially for the glassy state. We have pushed this comparison to the first memory-function level. It appears that the normal-mode analysis gives the correct short-time behavior, where correlated binary collisions play an important role. Such agreement extends toward intermediate times in the glassy state, where solidlike features are manifested by strong oscillations.