Recent advances in solid-state NMR computational spectroscopy: The case of alumino-silicate glasses

Solid-state NMR spectroscopy and computational approaches such as Molecular Dynamics (MD) simulations and Density Functional Theory have proven to be very useful and versatile techniques for studying the structure and the dynamics of noncrystalline materials if a direct comparison between experiment and theory is established. In this review, the basic concepts in first-principle modeling of solid-state NMR spectra of oxide glasses are presented. There are three theoretical ingredients in the computational recipe. First, classical or ab initio molecular dynamics simulations are employed to generate the structural models of the glasses of interest. Second, periodic Density Functional Theory calculations coupled with the gauge including projector augmented-wave (GIPAW) algorithm form the basis for the ab initio calculations of NMR parameters (chemical shielding and quadrupolar parameters). Finally, Spin-effective Hamiltonian are employed to simulate the solid-state NMR spectra directly comparable with the experimental counterparts. As an example of this methodology, the investigation of the local and medium range structure of Na-Ca silicate and aluminosilicate glasses that are usually employed as simplified models for basaltic, andesitic and rhyolitic magmas will be reported. We will show how the direct comparison of the theoretical NMR spectra of MD derived structural models with the experimental counterparts allows gaining new insights into the atomistic structure of very complex oxide glasses.