Nuclear Magnetic Resonance Study of Complex Molecular Crystals From First Principles: Case of Cholesterol

The layout of this thesis is as follows: In Chapter 2 we present the theoretical background relevant to our study, namely NMR, Density Functional Theory (DFT), PAW and GIPAW. We also report the performed computational tests that validate our implementation. In Chapter 3 we first give the experimentally determined structural properties of cholesterol crystals for all known phases and compare our theoretical results with these reports. In this chapter we also examine the adequacy of classical force field calculations in structure determination through comparisons with both ab initio results and experiment. In Chapter 4 we report our results for NMR spectrum of all known phases and comment on the accuracy of our calculations. Factors affecting the ab initio NMR calculations are investigated in detail, such as the impact of structural optimization and exchange-correlation functionals. A systematic error observed in GIPAW calculations is also discussed and a possible correction is proposed. We further test the validity of the introduced correction using the results of spectral editing experiments. Finally using all the information gathered, we perform peak assignment for the observed NMR spectra. We also compare the NMR spectrum obtained from molecules and crystals to draw conclusions on the intermolecular interactions present in cholesterol crystals.