NMR parameters in alkali, alkaline earth and rare earth fluorides from first principle calculations

Abstract

¹⁹F isotropic chemical shifts for alkali, alkaline earth and rare earth of column 3 basic fluorides are measured and the corresponding isotropic chemical shieldings are calculated using the GIPAW method. When using the PBE exchange–correlation functional for the treatment of the cationic localized empty orbitals of Ca²⁺, Sc³⁺ (3d) and La³⁺ (4f), a correction is needed to accurately calculate ¹⁹F chemical shieldings. We show that the correlation between experimental isotropic chemical shifts and calculated isotropic chemical shieldings established for the studied compounds allows us to predict ¹⁹F NMR spectra of crystalline compounds with a relatively good accuracy. In addition, we experimentally determine the quadrupolar parameters of ²⁵Mg in MgF₂ and calculate the electric field gradients of ²⁵Mg in MgF₂ and ¹³⁹La in LaF₃ using both PAW and LAPW methods. The orientation of the EFG components in the crystallographic frame, provided by DFT calculations, is analysed in terms of electron densities. It is shown that consideration of the quadrupolar charge deformation is essential for the analysis of slightly distorted environments or highly irregular polyhedra.