Computation of NMR shifts for paramagnetic solids

• Main Author: Mondal, Arobendo
• Other Authors: Kaupp, Martin, Technische Universität Berlin, Marek, Radek
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2019
• Subjects: 500 Naturwissenschaften und Mathematik; pNMR; EPR; fermi-contact; pseudocontact; solid-state; Fermikontakt; Pseudokontakt; Festkörper; Orca
• Online Access: https://depositonce.tu-berlin.de/handle/11303/8576; https://doi.org/10.14279/depositonce-7710

Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for studying the structural and electronic properties of paramagnetic solids such as battery materials, metal-organic frameworks, and molecular/ionic crystals. However, the interpretation of paramagnetic NMR spectra is often challenging as a result of the interactions of unpaired electrons with the nuclear spins of interest. In this thesis, we report a novel protocol to compute and analyze NMR chemical shifts for extended paramagnetic solids (pNMR), accounting comprehensively for Fermi-contact (FC), pseudo-contact (PC), and orbital shifts. This approach uses an EPR/NMR parameter-based formalism (hyperfine couplings, g-tensors, zero-field splitting ZFS D-tensors and orbital shieldings) for the computation of pNMR shifts. An incremental cluster model approach applied to the computation of g- and ZFS D-tensors has enabled the use of advanced multireference wave function methods (such as CASSCF or NEVPT2). The Gaussian-augmented plane-wave implementation of the CP2K code was used for periodic calculations whereas ORCA and Gaussian programs were used for more sophisticated molecular calculations. Due to the efficient and highly parallel performance of CP2K, a wide variety of materials with large unit cells can be studied with extended Gaussian basis sets. Using the developed protocol, the computed 7Li pNMR shifts for LixV2PO4 (x=3, 2.5, 2), as well as 7Li and 31P shifts of LiMPO4 (M=Mn, Fe, Co, Ni) /and MPO4 (M=Fe, Co) cathode materials are in good agreement with available experimental data. Importantly, the 7Li shifts in the high-voltage cathode material LiCoPO4 are dominated by spin-orbit-induced PC contributions, in contrast to previous assumptions, changing fundamentally interpretations of the shifts in terms of covalency. PC contributions are smaller for the 7Li shifts of the related LiMPO4 (M=Mn, Fe, Ni), where FC and orbital shifts dominate. The 31P shifts of all materials finally are almost pure FC shifts. Nevertheless, large ZFS contributions ...