Origin of NMR shielding in fluorides

Abstract

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 19 F nucleus in alkali fluorides, the main results are more general and can explain similar trends observed in other solids and for other nuclei.

Assessment of DFT functionals with NMR chemical shifts

“…32,33 The details are described in a previous publication 34 . Here we outline only the essential points necessary for further discussion.…”

“…5 is used as reference formula in order to discuss the physics, while the actual formulas specific to our augmented plane wave plus local orbital (APW+lo) implementation are given in Ref. 34. We stress that contrary to the reference formula Eq.…”

“…This is achieved by supplying additional local orbitals as described in Ref. 34. This extension is done for all orbital quantum numbers up to l + 1, where l is the maximal occupied orbital quantum number of the valence states of the specific atom.…”

NMR shieldings from density functional perturbation theory: GIPAW versus all-electron calculations

“…[10][11][12] In this paper, we benchmark the recent implementation (by several of us) of the linear response calculation of NMR shieldings within the GIPAW formalism of YPM in the Vienna Ab initio Simulation Package (VASP) 13 against all-electron APW+lo results for NMR shieldings in molecular and solid state systems and against non-relativistic LCAO calculations using DALTON (Ref. 14) and large uncontracted Gaussian basis sets.…”

“…The standard APW basis set is extended with eight additional local orbitals (NMR-LOs) at higher expansion energies for all "chemical" l + 1 angular momenta using a procedure described in Ref. 10. The Green's function used to represent the perturbation of the ground state is augmented with additional r ∂ ∂r u terms in order to accelerate convergence with respect to the number of NMR-LOs.…”