Si-O-Si bond-angle distribution in vitreous silica from first-principles Si-29 NMR analysis

The correlation between Si-29 chemical shifts and Si-O-Si bond angles in Si O2 is determined within density-functional theory for the full range of ang les present in vitreous silica. This relation closely reproduces measured s hifts of crystalline polymorphs. The knowledge of the correlation allows us to reliably extract from the experimental NMR spectrum the mean (151 degre es) and the standard deviation (11 degrees) of the Si-O-Si angular distribu tion of vitreous silica. In particular, we show that the Mozzi-Warren Si-O- Si angular distribution is not consistent with the NMR data. This analysis illustrates the potential of our approach for structural determinations of silicate glasses.