A DFT-Based Analysis of the NMR Fermi Contact Shifts in Tavorite-like LiMPO₄·OH and MPO₄·H₂O (M = Fe, Mn, V)

Complementing our work on the experimental measurements and DFT calculations of the NMR Fermi contact shifts for ⁷Li, ³¹P, and ¹H in the tavorite LiFePO₄·OH and homeotypic FePO₄·H₂O, LiMnPO₄·OH, MnPO₄·H₂O, and VPO₄·H₂O phases, we aim to understand the origin of those shifts. Using FP-LAPW calculations that were validated by reproducing correctly the experimental shifts, we analyze the electronic spin-transfer mechanisms from the transition metal M to the probed nucleus in relation with the electronic configuration of the M³⁺ ions and the nature of the chemical bonds in the compounds, by plotting the spin DOS and 2D or 3D spin density maps in selected energy domains. These mechanisms are analyzed in detail for the two Fe³⁺ phases, and the differences occurring for the Mn and V phases are discussed further