DFT calculations of magnetic shielding and quadrupolar coupling in ordered systems: methods and applications to NMR crystallography
Date
2017
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
This dissertation presents quantum-mechanical calculations of nuclear magnetic
resonance (NMR) parameters in crystalline solids. Several themes run through the
dissertation; they all relate to aspects of the prediction of magnetic-shielding tensors and
quadrupolar-coupling tensors for various light nuclides such as 13C, 15N, 17O, 19F, 29Si,
31P, 35Cl, and 43Ca. ☐ A cluster-based computational protocol for modeling NMR parameters in
molecular solids, referred to as the symmetry-adapted cluster ansatz, is discussed. This
approach uses a shell of molecules to represent the local lattice environment by
judiciously selecting molecules to maintain the rotational symmetry elements of the
crystal space group. Chapter 2 illustrates the utility of the cluster-based approach
through calculations of the principal components of the 13C magnetic-shielding tensors
of 155 carbon sites. In Chapter 3, this analysis is applied to the assignment of the 13C
chemical-shift tensors of the aromatic compound indigo. Chapter 4 focuses on
comparison of 13C, 15N, 19F, and 31P magnetic-shielding tensors calculated using the
cluster ansatz with results of using the periodic GIPAW approach. This analysis is
based on calculation of the magnetic-shielding tensors of 131 NMR-active sites in 72
materials. Furthermore, benchmark calculations are provided for a large number of
density functionals, including GGA, meta-GGA, and hybrid approaches. ☐ Chapters 5 and 6 expand the focus to the calculation of NMR parameters in
network solids. Chapter 5 presents 43Ca magnetic-shielding and quadrupolar-coupling
tensors in calcium carboxylates, and Chapter 6 presents 29Si and 31P magnetic-shielding
tensors in covalent network solids. In both chapters, the cluster-based approach is
benchmarked against the GIPAW approach, and various model chemistries are
assessed. The calculation of 29Si and 31P magnetic-shielding tensors employs an
approach in which the outermost atoms of the cluster are replaced with pseudoatoms
that reduce the overall charge on the cluster to permit SCF convergence. ☐ In addition to benchmarking cluster-based calculations of solid-state NMR
parameters, applications in NMR crystallography, based on computed 17O quadrupolar-coupling
tensors, are assessed. In particular, a method of semi-empirical geometry
optimization is proposed, in which a dispersion force field is parameterized to produce
structures that yield accurate predictions of 17O quadrupolar-coupling tensors.