Ab initio studies of the structural, dynamical and thermodynamical properties of graphitic and hydrogenated graphitic materials and their potential for hydrogen storage

The study presented in this PhD thesis is related to exploration of the properties of graphitic materials within the frame-work of ab initio methods. Structural and dynamical properties of graphitic materials are evaluated using the ab initio pseudopotential method. In graphitic materials, properties are obtained by incorporating Van der Waals interactions together with the generalized gradient approximation to density functional theory. These Van der Waals interactions improve the structural and dynamics of graphitic systems. In order to study the dynamical properties, the finite displacement method has been used to construct the dynamical matrix and force constant matrix. Phonon dispersions are investigated by the direct force constant matrix method in supercells. In this approach, force constants are assumed to be zero beyond a certain limit. Phonon frequencies are calculated from the force constant matrix. The dispersion relations and the Brillouin zone integrated density of states are also investigated. The significance of phonon dispersion has been studied to in various regions. Results are compared with dispersion corrected scheme and without dispersion corrected schemes to understand the importance of dispersion correction. Conclusions are also drawn on the applicability of theoretical approximations used. Further, ab initio results are also compared with the available data from experimental studies. The binding energies and electronic band gaps of exo-hydrogenated carbon nanotubes are determined to investigate the stability and band gap opening using density functional theory. The vibrational density of states for hydrogenated carbon nanotubes has been calculated to confirm the C-H stretching mode due to sp3 hybridization. The thermodynamical stability of hydrogenated carbon nanotubes has been explored in the chemisorption limit. Statistical physics and density functional theory calculations have been used to predict hydrogen release temperatures at standard pressure in zigzag and armchair carbon nanotubes