Theoretical Investigations of Selected Heavy Elements and Metal-hydrogen Systems by Means of Electronic Structure Calculations

Abstract: Using ab initio electronic structure calculations based on density functional theory the crystal, electronic and magnetic structures of selected materials have been investigated. The materials which are the subjects of these investigations can be divided into two groups. Parts of the investigations have concerned actinides and rare earths, heavy elements with an f-shell electronic configuration. Here the effects of delocalization on EuCo2P2 have been studied as well as the effect of including relativistic interactions when calculating the properties of thorium. For EuCo2P2 it was found that at a low pressure the valence state of Eu changes from divalent to trivalent with associated effects on the crystal structure and magnetic state.The other group of materials investigated are the metal-hydrogen and metal- lithium systems. Both of these have an important technological application in the form of batteries. Here the emphasis of the investigations has been the fundamental understanding of the mechanism of hydrogenation, and a novel theory explaining the driving force behind hydrogenation is suggested. Vanadium hydride, VHx, has been examined in detail and the reason for the anomalous non-isotropic expansion is explained. A scheme to make vanadium magnetic is also proposed. Finally a method based on electron-hole coupled Green's functions has been used to facilitate the comparison between calculated electronic structures and X-ray absorption spectra. In connection to this a novel theory of charge transfer in the X-ray absorption process applied to transition metal oxides and lithium intercalated transition metal oxides is presented.