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Signature of small rings in the Raman spectra of normal and compressed amorphous silica: A combined classical and ab initio study

2003; American Physical Society; Volume: 68; Issue: 18 Linguagem: Inglês

10.1103/physrevb.68.184202

1095-3795

A. Rahmani, Magali Benoit, Claude Benoît,

High-pressure geophysics and materials

We calculate the parallel (VV) and (VH) perpendicular polarized Raman spectra of amorphous silica. Model ${\mathrm{SiO}}_{2}$ glasses, uncompressed and compressed, were generated by a combination of classical and ab initio molecular-dynamics simulations and their dynamical matrices were computed within the framework of the density-functional theory. The Raman-scattering intensities were determined using the bond-polarizability model and a good agreement with experimental spectra was found. We confirm that the modes associated to the fourfold and threefold rings produce most of the Raman intensity of the ${D}_{1}$ and ${D}_{2}$ peaks, respectively, in the VV Raman spectra. Modifications of the Raman spectra upon compression are found to be in agreement with experimental data. We show that the modes associated to the fourfold rings still exist upon compression but do not produce a strong Raman intensity, whereas the ones associated to the threefold rings do. This result strongly suggests that the area under the ${D}_{1}$ and ${D}_{2}$ peaks is not directly proportional to the concentration of small rings in amorphous ${\mathrm{SiO}}_{2}.$