Na super(+) as a probe to structural investigation of dehydrated smectites using NMR spectra calculated by DFT

Ab initio calculations based on density-functional theory (DFT) were made to a large ensemble of representative models of dehydrated smectites with Na super(+) as counterion. The structures were generated by different isomorphic substitutions of Al super(3+) by Mg super(2+) in octahedral sheet and Si super(4+) by Al super(3+) in tetrahedral sheet followed by full optimization of the geometries. Structures were chosen among the lowest total energies to calculate nuclear magnetic resonance (NMR) parameters of super(1)H, super(27)Al, super(29)Si, super(25)Mg and super(23)Na by means of gauge including projector augmented wave (GIPAW) method. The calculated NMR parameters and simulated spectra suggest that Na super(+) can be a good probe to investigate the layer structure. The spectra shape for super(23)Na is more sensitive to isomorphic substitutions in the layer than the other nuclei.