Origin of NMR shielding in fluorides
In this work, we analyze in detail the relation between electronic structure and fluorine nuclear magnetic resonance (NMR) shielding in a series of solid state alkali fluorides (LiF, NaF, KF, RbF, and CsF). For that purpose, we use solid-state NMR calculations implemented in the density functional theory full potential WIEN2K code (APW + lo). Both measurements and calculations show that the NMR shielding varies across the series by approximately 200 ppm. We focus our discussion on an explanation of the origin of the observed trend, and we show that the variation is mainly determined by contributions from “semicore” metal-p and valence F-p bands. More specifically, the trend in fluorine shielding can be related to the small but significant change in the hybridization of these states. A second important ingredient determining the value of the shielding is the presence and position of metal-d states in the unoccupied part of the Kohn-Sham bands. Although the present analysis has been demonstrated for the 19F nucleus in alkali fluorides, the main results are more general and can explain similar trends observed in other solids and for other nuclei.
127I NMR calculations in binary metal iodides by PBE-GGA, YS-PBE0 and mBJ exchange correlation potentials.
We have calculated Nuclear Magnetic Resonance (NMR) spectroscopy for 127I (quadrupolar nuclei I=5/2) in binary metal iodides XI (X=Li, Na, K, Rb and Cs) by using PBE- GGA, YS- PBE0 and mBJ exchange correlation potentials. The results show that the nature of bonds between Iodine and metal atoms are ionic. The main contribution in NMR spectroscopy is related to the induced current inside the atomic sphere and the remainder of the unit cell volume contributes only a few ppm. Obtained NMR shifts are compared with the NMR shielding data and the NMR shielding for metal-p band varies across the series about 221ppm. Density of states results indicate that the largest contribution in the shielding comes from the I-core electrons (1s and 4d). The NMR shielding graphs show that there are negative linear correlation with slope -1.18, -1.16 and -1.01 by PBE- GGA, YS- PBE0 and mBJ, respectively. The computed results by mBJ are in good agreement with the experimental values.
Ordre local dans quelques verres fluores du systeme PbF2MIItF2MIIItF3 par EXAFS
Abstract The local environment of transition metal ( M t ) and lead has been studied by EXAFS for some fluoride glasses in the system PbF 2  M II t F 2  M III t F 3 ( M II t = Mn 2+ , Zn 2+ ; M III t = Fe 3+ , Ga 3+ ). Theoretical phase shifts and backscattering amplitude are used after testing with crystallized fluorides of various structures. Transition metals are sixfold coordinated and M t F distances are very close to those known in crystallized compounds. Lead has eight to nine fluorine neighbors forming a very distorted polyhedra. Radial distributions, partially corrected for phase shifts, show a very weak second peak but the second neighbors nature and the distances cannot be determined without ambiguity.