Wednesday, May 22, 2013

1305.4796 (Filipe Vasconcelos et al.)

Extended Czjzek model applied to NMR parameter distributions in sodium
metaphosphate glass

Filipe Vasconcelos, Sylvain Cristol, Jean-François Paul, Laurent Delevoye, Francesco Mauri, Thibault Charpentier, Gérard Le Caër
The Extended Czjzek Model (ECM) is applied to the distribution of NMR parameters of a simple glass model (sodium metaphosphate, $\mathrm{NaPO_3}$) obtained by Molecular Dynamics (MD) simulations. Accurate NMR tensors, Electric Field Gradient (EFG) and Chemical Shift Anisotropy (CSA), are calculated from Density Functional Theory (DFT) within the well-established PAW/GIPAW framework. Theoretical results are compared to experimental high-resolution solid-state NMR data and are used to validate the considered structural model. The distributions of the calculated coupling constant $C_Q\propto |V_{zz}|$ and of the asymmetry parameter $\eta_Q$ that characterize the quadrupolar interaction are discussed in terms of structural considerations with the help of a simple point charge model. Finally, the ECM analysis is shown to be relevant for studying the distribution of CSA tensor parameters and gives new insight into the structural characterization of disordered systems by solid-state NMR.
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