Electronic structure theory of complex materials and nanotubes

We developed and applied the pseudopotential density functional theory (DFT) method to two areas of broad scientific interest as well as practical use. One area is NMR chemical shifts to study magnetic response of condensed matter systems such as carbon nitride compounds and amino acid crystals. The other area is electrical transport properties of carbon nanotube systems such as crossed-tube junctions and nano-peapods. In both applications, new developments in DFT first-principles calculations play a key role in predicting quantum mechanical material properties accurately. Chapter one introduces the general topic of the first-principles pseudopotential DFT approach. Chapter two explains various theoretical aspects of NMR chemical shifts with necessary technical details. Chapter three and chapter four deal with application of NMR chemical shifts calculations to hard carbon nitrides and amino acid crystals. Chapter five introduces carbon nanotubes and the theoretical details of calculating electrical transport properties of the carbon nanotube systems. Chapter six and chapter seven deal with electrical transport properties of crossed carbon nanotube junctions and nano-peapods. Chapter eight supplements the discussion of the first-principles transport physics by considering one analytical model approach to the quantum conductance of multiwall carbon nanotubes. We demonstrated that the various phases of the predicted carbon nitride may be distinguished by NMR measurements, and our analysis of the NMR spectra of crystalline amino acids reveals the importance of intermolecular interaction. The calculated electrical conductance of crossed carbon nanotube junctions is consistent with the unexpectedly large intertube currents seen in experiment and quantitatively predicts the deformation-driven currents under varying contact force. Electrical conductance study of carbon nano-peapods shows that there is resonant backscattering at the molecular fullerene levels and that the resonance position can be manipulated.