First-Principles Nuclear Magnetic Resonance Structural Analysis of Vitreous Silica

Gauge including projector augmented wave (GIPAW) NMR calculations combined with hybrid Monte Carlo/molecular dynamics simulations are carried out in order to investigate the relationships between the oxygen-17 and silicon-29 NMR spectra of vitreous silica and its local structure in terms of the Si-O-Si bond angle and Si-O distance distributions. Special attention is paid to the structure and NMR parameters of,three- and four-membered rings, and the effect of their concentration on glass density is studied. It is shown that our simulations provide a new insight into the features of the O-17 NMR parameters distribution. Accordingly, a new analytical model is presented and applied for the reconstruction of the Si-O-Si angle from the NMR spectrum. The reliability of the procedure is demonstrated conclusively through the excellent consistency of the analysis of the oxygen-17 and silicon-29 NMR experimental data of vitreous silica. Si-O-Si angle distribution mean values of 147.1 degrees and 148.4 degrees, respectively, and standard deviations of 11.2 degrees and 10.8 degrees, respectively, are obtained from the oxygen-17 and silicon-29 NMR experimental spectrum (Clark et al., ref 4) of the same sample.