The energetics of hydrogen in aluminium calculated from first principles

The energetics and electronic structure of an isolated hydrogen impurity in bulk aluminium and in the aluminium-vacancy system are studied by ab initio methods. The calculations are based on the local density approximation and the supercell approach, with a norm-conserving pseudopotential for aluminium and the bare Coulomb potential for hydrogen. The relaxed electronic ground state is determined by the conjugate-gradients technique. Results are presented for the heat of solution, the relative energies of different interstitial sites, the energy profile for migration of hydrogen between sites, and the trapping energy and equilibrium location of hydrogen bound to a vacancy. The heat of solution is close to the measured value, and the tetrahedral site is energetically favoured over the octahedral site, as indicated by experiment, though the energy difference between the sites is comparable with the uncertainties in the calculations. Hydrogen is found to be bound to the vacancy in a strongly off-centre position, with a binding energy that is somewhat smaller than the experimental value.