Résumé:

We have studied the structural properties of two (Li/Na) single-alkali silicate glasses with the same cation content (i.e. 20\%) by combined classical and Car-Parrinello molecular dynamics simulations. The influence of the network modifier nature on the relevant structural parameters have been further examined in terms on their correlations to the first-principles NMR spectra and parameters computed for our glassy models using the GIPAW method. Hence, we found that the \Si isotropic chemical shift of \Q4 units upon the mean Si-O-T bond angle (where T denotes the Q${}^{(n)}$ connected tetrahedron, $n=4,3,2$). could be well described by means of a {\it single} (i.e. the same for both glasses) simple linear dependence.