Combined Si-29 double quantum NMR and MD simulation studies of network connectivities of binary Na2O center dot SiO2 glasses: new prospects and problems

Quantitative results of structural studies of binary xNa(2)O . (1 - x)SiO2 glasses (x = 0.15, 0.20, 0.25), using both experimental (double quantum NMR ) and theoretical methods (molecular dynamics simulation), are presented. T he primary goal is to verify and quantify connectivities of the various SiO 4 species in terms of small clusters of Q(n.ijkl) units, with n being the n umber of bridging oxygen atoms of the 'central' Q unit, The additional supe rscripts denote the Q character of the bonded adjacent SiO4 tetrahedra. It is the aim of the paper to compare these DQ NMR results with theoretical pr edictions by the most recent MD simulations. The current problems and limit ations of this new approach are discussed in detail. (C) 2001 Elsevier Scie nce B.V. All rights reserved.