Sommaire:

Raman spectroscopy is one of the key experimental methods for the structural analysis of glasses, thanks to its simple application and its sensitivity to variations of composition or atomic-scale order. However, the inherent disorder of the glassy structure results to broad and overlapping peaks in the spectra, rendering their quantitative analysis a challenging task and resulting in a mostly phenomenological interpretation. This drawback can be addressed by the use of modern and accurate theoretical tools, such as ab-initio vibrational spectroscopies. In this work we have studied some simple sodosilicate glasses and we have used density functional theory (DFT) to calculate their vibrational density of states, as well as their Raman and IR spectra. The main advantage of the DFT calculations is that the resulting spectra can be directly correlated with the structural models and, most importantly, the vibrational spectrum can be decomposed into exact contributions arising from individual structural units. In the case of the sodosilicate glasses, we have identified correlations between spectral characteristics and stoichiometry, the effect of the presence of bridging and non-bridging oxygens, the contributions of smaller or larger Si-O-Si angles, as well as the ones arising from the presence of the so-called Q-species. These results open the way for the study of even more complex glasses and aid in the interpretation of experimental spectra.

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