Electron structure of single and interacting hydrogen impurities in free-electron-like metals

Recent progress in the theoretical description of hydrogen impurities in metals, as described by the jellium model, and their interaction mutually and with vacancies are described. In addition to giving a detailed account of the author's contribution, the paper presents new results for the spectra of the hydrogen-induced states. These show for single interstitial hydrogen a doubly occupied bound state, while substitutional hydrogen has an atomic resonance in the conduction band. In both cases the state is situated just below the "local bottom of the band, " as defined by the clean-metal effective potential at the impurity site. When two such states interact, both the bonding and the antibonding molecular orbitals get filled except at the lowest metallic densities, and a repulsive hydrogen-hydrogen interaction results. Spin-polarized self-consistent-field calculations of the impurity excitation energies are presented. The results compare well with the one-electron binding energies of the bound states and with the excitation energies calculated by Vinter. The hydrogen impurity spectra presented can therefore be expected to represent approximately experimental excitation spectra of interstitial and substitutional hydrogen in free-electron-like metals.