Evidence for instantaneous resonant modes in dense fluids with repulsive Lennard-Jones force

In terms of instantaneous-normal-mode (INM) analysis and a newly defined me asure for quasilocalization, we present the evidence for the resonant modes in a model fluid, in which the pair interaction is merely the repulsive po rtion of the Lennard-Jones potential. We name such a quasilocalized INM as an instantaneous resonant mode (IRM). By examining the potential energy pro file beyond the INM approximation, we conclude that the IRMs occur in singl e-well potentials with strong enough anharmonicity. (C) 1999 American Insti tute of Physics. [S0021-9606(99)50301-2].