Ref Arxiv: cond-mat/0306332
Ref. & Cit.: NASA ADS
Résumé:

We have determined the vibrational properties of a sodium tetrasilicate(Na$_{2}$Si$_{4}$O$_{9}$) glass model generated by molecular dynamicssimulations. The study has been carried out using a classical valence forcefields approach as well as an {\it ab initio} approach in the framework of thedensity functional theory. The total and partial vibrational densities ofstates (VDOS) are presented, as well as some characteristics of the vibrationalmodes (participation ratios, correlation lengths). For the low-frequency bandsbelow 500 cm${}^{-1}$, we find that the shapes of the two calculated VDOS aswell as those of their corresponding partial VDOS are quite similar. For theintermediate- and high-frequency ranges, we observe larger discrepanciesbetween the two calculations. Using the eigenmodes of the dynamical matrix wealso calculate the polarized Raman spectra within the bond-polarizabilityapproximation. We find an overall agreement between the calculated parallelpolarized (VV) Raman spectra and the corresponding experimental spectrum.Regarding the perpendicular depolarized (VH) Raman spectrum, the comparison ofthe calculated spectra to the experimental data indicates a need for anadjustment of the VH bond-polarizability parameters.

Commentaires: 17 pages, 4 EPS figures, submitted to J. Non. Cryst.-Sol., corrected version following referee's comments