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Parlinski, Li, and Kawazoe Reply: In a recent Letter [1], we have calculated the soft mode in the cubic ZrO 2 using the standard CASTEP ab initio program [2], with the local-density approximation and pseudopotential approach, and confining the studied crystallite to a 2 3 2 3 2 fcc supercell with periodic boundary conditions and 96 atoms. The force constants were directly derived from Hellmann-Feynman (HF) forces induced by separate Zr and O atomic displacements. Detraux, Ghosez, and Gonze [3] commented that for ZrO 2 the Born effective

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We compare the atomic dynamics of the glass to that of the relevant crystal. In the spectra of inelastic scattering, the boson peak of the glass appears higher than the transverse acoustic (TA) singularity of the crystal. However, the density of states shows that they have the same number of states. Increasing pressure causes the transformation of the boson peak of the glass towards the TA singularity of the crystal. Once corrected for the difference in the elastic medium, the boson peak matches the TA singularity in energy and height. This suggests the identical nature of the two features.