DISPERSION-RELATION FOR COLLECTIVE MODES IN CLASSICAL MONATOMIC LIQUIDS AND AMORPHOUS SOLIDS - REPLY

We reply to the Comment by Knipp [Phys. Rev. A 41, 4547 (1990)]. We show that Knipps proposal for the dynamical structure factor S(k,) should be extended away from long wavelength by a suitable choice of (k) generalizing the ratio of the specific heats ==(0). The choice (k)=BS(k)/BT(k) leads back to our original proposal for the dispersion relation of the collective mode in a liquid metal like Rb, BS and BT being adiabatic and isothermal bulk moduli. © 1990 The American Physical Society.