Hybrid density functional studies of hydrogen storage related molecular systems.

摘要

A major obstacle to the conversion to a "hydrogen economy" is the problem of onboard hydrogen storage. Despite decades of extensive effort no material has been found that has the combination of high gravimetric hydrogen density, adequate hydrogen dissociation energetics, long-term cyclability, and low cost required for commercial vehicular application. This thesis does not solve the hydrogen storage problem, but is a series of hybrid density functional studies aiming to addresses a limited number of issues related to materials that have been or are candidates for hydrogen storage applications.; After an introduction (Chapter 1), and a review of the theoretical methods and models used in these studies (Chapter 2), in Chapter 3 we investigate the adequacy of broken-symmetry unrestricted density functional theory (DFT) for constructing the potential energy curve of nickel dimer and nickel hydride, as model for larger bare and hydrogenated nickel cluster calculations.; The rest of the thesis is concerned with studies of alanates, which have recently been discovered to function as a reversible hydrogen storage system in the presence of titanium. In Chapter 4 we present a basis set benchmarking study aimed at finding the smallest basis set that gives an acceptable accuracy for the molecular systems containing aluminum, hydrogen and titanium. A short Chapter 5 presents a study of aluminum dimer, that we encountered during our basis set benchmarks and surprised us by its long debated ground state, which has only relatively recently unambiguously characterized. In Chapter 6, we study the structure and stability of simple and mixed aluminum and titanium hydrides and clusters, along with a very intriguing 12-nuclear complex combination {lcub}[(eta5-C5H5)2Ti(mu-H)]2[(eta 5-C5H5)Ti(mu-H2)] Al3(mu-H 4)(H){rcub}2, which contains two trinuclear aluminum clusters bonded by both hydrogen bridges and direct metal-metal bonds.