Self-trapped hydrogen states in metals determined from quantum mechanical calculations using potentials based on ab initio data: I. Hydrogen isotopes in Pd

Ab initio pseudopotential calculations for H in Pd are used in order to construct an auxiliary short-ranged host-lattice-particle potential which well reproduces the large number of available ab initio data. This potential (instead of an empirical potential as employed in previous treatments) is used in a quantum mechanical calculation of hydrogen as well as of mu + and pi + states in Pd, which takes into account the dependence of the lattice relaxation on particle mass and particle state. These calculations allow us to determine Jahn-Teller coupling constants of excited states and the dependence of lattice displacements on the isotopic mass. It is found that coupling to lattice modes with E-symmetry is dominant. The effect of lattice relaxation on the total energy difference if hydrogen is localized at tetrahedral or octahedral sites and on the excitation energies as measured by inelastic neutron scattering experiments is also discussed.