Collective dynamics at high wave vector in the glass-forming liquid Ca0.4K0.6(NO3)(1.4)

The nature of the phonons at high wave vectors (0.2 <k <7.0 Angstrom (-1)) in the glass-forming liquid Ca0.4K0.6(NO3)(1.4) has been investigated by us ing molecular dynamics (MD) simulations. The MD simulations have been perfo rmed with a previously proposed polarizable model for the nitrate anion [M. C. C. Ribeiro, Phys. Rev. B 61, 3297 (2000)]. Time correlation functions o f mass and charge current fluctuations have been calculated in order to obt ain the spectra of the acoustic and the optic modes, respectively, both the longitudinal and the transverse ones (LA, TA, LO, and TO). Phonon dispersi on curves, omega (k), and the damping, Gamma (k), of the LA modes are shown to oscillate out of phase with the static structure factor, S(k), in a wid e range of wave vectors. Corresponding dynamic structure factors, S(k,omega ), are calculated as k-dependent, omega -constant cuts of the LA spectra. I t is shown that S(k,omega) oscillates in phase with S(k) for low energy mod es. A similar analysis is applied to the LO spectra, the corresponding dyna mic structure factor following the charge static structure factor, S-q(k). (C) 2001 American Institute of Physics.