Theoretical Prediction of Nuclear Quadrupole Resonance Spectra of Aluminum, Bromine and Nitrogen Compounds via First Principles Calculations

Author

Chris Harwell, Louisiana State University and Agricultural and Mechanical College

Date of Award

8-2000

Document Type

Thesis

Abstract

We study the interaction of the electric field gradient (EFG) and the nuclear quadrupole moment of ⁸¹Br,²⁷Al, and ¹⁴N nuclei via ab initio quantum chemistry calculations. The primary goal is to predict the nuclear magnetic resonance (NMR) spectral parameters of interesting materials and assist in interpretation of their spectra. The calculations predict NMR spectral parameters for:

1. ²⁷Al nuclei in andalusite, sillimanite and kyanite - three polymorphs of Al2Si05 - for assigning NMR signals to crystallographic sites, as a zeolite model and studying the effect of structural changes due to temperature (25-1000''C);
2. ¹⁴N nuclei in tetryl and tetryl mimics to predict transition frequencies for the detection of explosives.
3. ⁸¹Br nuclei in brominated aromatic flame retardants and models to assist in spectra interpretation for judging dispersal in high impact polystyrene;
4. ²⁷Al nuclei in cyclic (N-Al)i molecules for their similarity to the industrially important catalyst methyl-aluminum-oxane.

The calculations use standard quantum chemistry computer programs. We examine single molecules with molecular orbital (MO) theory and full crystals with full potential linearized augmented plane wave (FP-LAPW) density functional theory. We also explore parts of full crystals by using MO theory for a small atom cluster and point charges for surrounding atoms. The MO calculations employ the restricted Hartree-Fock and the Becke's 3-parameter Lee-Yang-Parr hybridized density functional theory methods. We compare calculated spectral parameters among the different methods and with literature values acquired from experiment. The FP-LAPW method best predicts the spectral parameters and magnitudes, though it does rely on good quality crystal data being available. For MO theory a fairly large basis set of at least triple zeta quality with additional polarization and tight functions is necessary for accurate spectral parameters, and this method works well for single molecules for which crystal data may not be available.

Recommended Citation

Harwell, Chris, "Theoretical Prediction of Nuclear Quadrupole Resonance Spectra of Aluminum, Bromine and Nitrogen Compounds via First Principles Calculations" (2000). LSU Historical Dissertations and Theses. 8364.
https://repository.lsu.edu/gradschool_disstheses/8364

DOI

10.31390/gradschool_disstheses.8364