Instantaneous normal modes of Na in supercooled liquid and glassy states

The instantaneous-normal-mode (INM) densities of states (DOS) of Na in the supercooled-liquid and glassy states under constant pressure have been calculated via molecular-dynamics simulation, with a rapid quenching rate for the glassy states. In the glassy states, at frequencies less than omega(m), the frequency corresponding to the lowest-lying traveling waves permitted by the simulated system, the real-frequency INM DOS, strongly deviates from the liquidlike behavior, which is linearly dependent in frequency, but still has a great enhancement as compared with the phonon DOS of the Debye model for crystals. At T = 5 K, peaks in the distribution of the INM participation ratio are observed at frequencies around omega(m) and root 2 omega(m), the latter corresponding to the second lowest-lying traveling waves. [S0163-1829(98)05325-9].