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

TL;DR

This study combines experimental NMR measurements with first-principles calculations to accurately predict fluorine chemical shifts and quadrupolar parameters in various fluoride compounds, highlighting the importance of correction methods and electron density analysis.

Contribution

It introduces a correction approach for PBE functional in calculating 19F chemical shieldings and demonstrates the use of DFT to analyze quadrupolar parameters and EFG orientations in fluoride crystals.

Findings

Correlation between experimental shifts and calculated shieldings enables accurate NMR spectrum prediction.

Correction methods improve the accuracy of PBE-based calculations for certain cations.

DFT analysis of EFGs provides insights into electron density distribution in distorted environments.

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 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 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 gradient 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 term 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.